feat: attach desktop file paths as editable learner chips

components/answered-card.tsx

@@ -4,6 +4,7 @@ import { useState } from "react";
 import { ConfidenceRail } from "@/components/confidence-rail";
 import { GlyphMark } from "@/components/ui/glyph-mark";
 import { ThinkingBlock } from "@/components/thinking-block";
+import { PathText } from "@/components/file-path-chip";
 import { cn } from "@/lib/utils";
 import { ToolContentResponse } from "@/components/ai-elements/message";
 import type { QuestionAnswerData } from "@/src/core";
@@ -153,13 +154,13 @@ export function AnsweredCard({ answer: savedAnswer, input }: { answer: QuestionA
 							data-testid="answered-other"
 							className="flex items-center gap-2 rounded-lg border border-primary bg-accent px-3 py-1.5"
 						>
-							<span>“{answer.other}”</span>
+							<span>“<PathText text={answer.other} />”</span>
 						</div>
 					)}
 				</div>
 			)}
 
-			{answer.text && <div className="lh-prose mt-2 whitespace-pre-wrap">“{answer.text}”</div>}
+			{answer.text && <div className="lh-prose mt-2 whitespace-pre-wrap">“<PathText text={answer.text} />”</div>}
 
 			{/* The confidence record (owner round 6): the slider's rail, disc
 			    removed — the missing handle itself says "this is a record, not a

components/chat.tsx

@@ -14,6 +14,7 @@ import {
 	ConversationScrollButton,
 } from "@/components/ai-elements/conversation";
 import { Message, MessageContent, MessageResponse } from "@/components/ai-elements/message";
+import { PathText } from "@/components/file-path-chip";
 import { Reasoning, ReasoningContent, ReasoningTrigger } from "@/components/ai-elements/reasoning";
 import { Shimmer } from "@/components/ai-elements/shimmer";
 import { BrailleSpinner } from "@/components/braille-spinner";
@@ -687,10 +688,10 @@ export function Chat({
 	const cycleChatFields = useCallback((): readonly HTMLElement[] => {
 		const pick = (sel: string) => Array.from(document.querySelectorAll<HTMLElement>(sel));
 		return [
-			...pick('[data-testid="reading-thinking-field"] textarea'),
-			...pick('[data-testid="question-dock"] textarea'),
-			...pick('[data-testid="practice-dock"] textarea'),
-			...pick('[data-testid="composer"] textarea'),
+			...pick('[data-testid="reading-thinking-field"] [data-file-path-input]'),
+			...pick('[data-testid="question-dock"] [data-file-path-input]'),
+			...pick('[data-testid="practice-dock"] [data-file-path-input]'),
+			...pick('[data-testid="composer"] [data-file-path-input]'),
 		];
 	}, []);
 	useFieldCycle(cycleChatFields);
@@ -705,7 +706,7 @@ export function Chat({
 	 * composer: with a question pending the Composer is unmounted, the ref
 	 * is null, and the thinking field is left alone by design. */
 	const dictationWasActiveRef = useRef(false);
-	const composerInputRef = useRef<HTMLTextAreaElement>(null);
+	const composerInputRef = useRef<HTMLDivElement>(null);
 	useEffect(() => {
 		if (dictation.active) {
 			dictationWasActiveRef.current = true;
@@ -1507,7 +1508,7 @@ export function Chat({
 												    rail as the thinking rows — one quote geometry. */}
 												<div className="font-medium uppercase tracking-wide text-muted-foreground">You</div>
 												<div className="lh-prose whitespace-pre-wrap text-foreground">
-													{m.parts.filter((p) => p.type === "text").map((p) => p.text).join("\n")}
+													<PathText text={m.parts.filter((p) => p.type === "text").map((p) => p.text).join("\n")} />
 												</div>
 											</div>
 									) : (

components/composer.tsx

@@ -3,6 +3,7 @@
 import { ArrowRightIcon, CornerDownLeftIcon, SquareIcon } from "lucide-react";
 import { cn } from "@/lib/utils";
 import { Hint } from "@/components/ui/hint";
+import { PathInput } from "@/components/path-input";
 
 /**
  * The chat composer — content row ONLY (the persistent rounded shell lives in
@@ -59,7 +60,7 @@ export function Composer({
 	autoFocus?: boolean;
 	/** The page's handle to the textarea — the dictation-end focus (owner,
 	 *  2026-10-01): a run ending hands the cursor to the bare composer. */
-	inputRef?: React.RefObject<HTMLTextAreaElement | null>;
+	inputRef?: React.RefObject<HTMLDivElement | null>;
 	/** Escape while a dictation runs stops it (STT wave, 2026-09-17). No-op
 	 *  when absent — Esc otherwise means nothing in the composer. */
 	onEscape?: () => void;
@@ -90,10 +91,11 @@ export function Composer({
 				act();
 			}}
 		>
-			<textarea
+			<PathInput
 				ref={inputRef}
 				value={value}
-				onChange={(e) => onChange(e.target.value)}
+				onValueChange={onChange}
+				defaultDropTarget
 				onKeyDown={(e) => {
 					// Esc ends dictation before anything else Esc might someday mean
 					// here (the dictate decisions: click-again or Esc to stop).
@@ -115,7 +117,6 @@ export function Composer({
 				}}
 				placeholder={placeholder}
 				autoFocus={autoFocus}
-				rows={1}
 				className="field-sizing-content lh-input max-h-48 min-h-10 flex-1 resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground"
 			/>
 			{/* The button follows the text (owner report 2026-10-03): while

components/dictation.tsx

@@ -199,6 +199,17 @@ export function rmsToMeter(rms: number): number {
  * window, one pending question, one target at a time.
  */
 let questionTarget: ((text: string) => void) | null = null;
+let composerTarget: ((text: string) => void) | null = null;
+
+/** File references use the very same default destination as dictation,
+ * including claims whose dock is currently collapsed. A focused editor can
+ * insert at its caret instead; callers use this only as the fallback. */
+export function appendToPrimaryInput(text: string): boolean {
+	const target = questionTarget ?? composerTarget;
+	if (!target) return false;
+	target(text);
+	return true;
+}
 
 /* The finisher registry: submit paths FAR from the hook's owner (the
  * pending question's dock) need finish() without a prop bridge. Same
@@ -280,6 +291,13 @@ export function useDictation({ append }: { append: (text: string) => void }): Di
 	 *  retarget (composer↔question) is honored on the very next final. */
 	const appendRef = useRef(append);
 	appendRef.current = append;
+	useEffect(() => {
+		const target = (text: string) => appendRef.current(text);
+		composerTarget = target;
+		return () => {
+			if (composerTarget === target) composerTarget = null;
+		};
+	}, []);
 
 	// Live machinery (non-render values). The MediaStream tracks stop and
 	// the per-run nodes disconnect on teardown; the socket is recreated per

components/file-path-chip.tsx

@@ -0,0 +1,62 @@
+import React, { Fragment } from "react";
+import {
+	File,
+	FileArchive,
+	FileAudio,
+	FileCode,
+	FileImage,
+	FileSpreadsheet,
+	FileText,
+	FileVideo,
+} from "lucide-react";
+import { filePathLabel, parseFilePaths } from "@/src/core";
+
+function fileIcon(label: string) {
+	const extension = label.split(".").at(-1)?.toLowerCase();
+	if (/^(png|jpe?g|gif|webp|svg|bmp|tiff?|avif|heic)$/.test(extension ?? "")) return FileImage;
+	if (/^(mp3|wav|ogg|flac|m4a|aac)$/.test(extension ?? "")) return FileAudio;
+	if (/^(mp4|mov|webm|mkv|avi)$/.test(extension ?? "")) return FileVideo;
+	if (/^(zip|gz|tar|bz2|xz|7z|rar)$/.test(extension ?? "")) return FileArchive;
+	if (/^(csv|tsv|xlsx?|ods)$/.test(extension ?? "")) return FileSpreadsheet;
+	if (/^(js|jsx|ts|tsx|py|rb|rs|go|c|cpp|h|java|json|html|css|sh|yaml|yml)$/.test(extension ?? "")) return FileCode;
+	if (/^(pdf|txt|md|mdx|rtf|docx?|odt|tex|epub)$/.test(extension ?? "")) return FileText;
+	return File;
+}
+
+export interface FilePathChipProps {
+	path: string;
+	/** Editors can make the chip atomic; transcript renderers can omit this. */
+	contentEditable?: false;
+	className?: string;
+}
+
+/** Pure presentation: no links, open actions, HTML injection or path probing. */
+export function FilePathChip({ path, contentEditable, className }: FilePathChipProps) {
+	const label = filePathLabel(path);
+	const Icon = fileIcon(label);
+	return (
+		<span
+			role="img"
+			aria-label={path}
+			title={path}
+			contentEditable={contentEditable}
+			className={`inline-flex max-w-full items-center gap-1 rounded border bg-muted/50 px-1.5 py-0.5 align-middle text-sm${className ? ` ${className}` : ""}`}
+		>
+			<Icon aria-hidden="true" className="size-3.5 shrink-0" />
+			<span className="min-w-0 truncate">{label}</span>
+		</span>
+	);
+}
+
+/** Ordinary learner text stays ordinary text; only quoted paths become chips. */
+export function PathText({ text }: { text: string }) {
+	return (
+		<>
+			{parseFilePaths(text).map((part) => (
+				<Fragment key={part.start}>
+					{part.kind === "path" ? <FilePathChip path={part.path} /> : part.text}
+				</Fragment>
+			))}
+		</>
+	);
+}

components/file-path-drop-zone.tsx

@@ -0,0 +1,106 @@
+"use client";
+
+import { useEffect, useRef, useState } from "react";
+import { FileSymlinkIcon, XIcon } from "lucide-react";
+import { quoteFilePath } from "@/src/core";
+import { appendToPrimaryInput } from "@/components/dictation";
+import { INSERT_FILE_PATHS_EVENT } from "@/components/path-input";
+
+const BROWSER_NOTICE = "Local file paths can only be attached in the desktop app. You can paste a full path instead.";
+
+/** The content area only: the sidebar is deliberately outside this zone.
+ * Existing files stay where they are; only quoted path strings enter drafts. */
+export function FilePathDropZone({ children, className }: { children: React.ReactNode; className?: string }) {
+	const root = useRef<HTMLElement>(null);
+	const depth = useRef(0);
+	const [dragging, setDragging] = useState(false);
+	const [notice, setNotice] = useState("");
+	const hasFiles = (event: React.DragEvent) => Array.from(event.dataTransfer.types).includes("Files");
+	const clearDrag = () => { depth.current = 0; setDragging(false); };
+	useEffect(() => {
+		// The sidebar remains a non-target, but dropping a file there must not
+		// navigate the app away. No indicator or attachment is produced there.
+		const preventOutsideNavigation = (event: DragEvent) => {
+			if (Array.from(event.dataTransfer?.types ?? []).includes("Files")
+				&& event.target instanceof Node && !root.current?.contains(event.target)) event.preventDefault();
+		};
+		window.addEventListener("dragover", preventOutsideNavigation);
+		window.addEventListener("drop", preventOutsideNavigation);
+		return () => {
+			window.removeEventListener("dragover", preventOutsideNavigation);
+			window.removeEventListener("drop", preventOutsideNavigation);
+		};
+	}, []);
+	return (
+		<main
+			ref={root}
+			className={className}
+			data-testid="file-path-drop-zone"
+			onDragEnter={(event) => {
+				if (!hasFiles(event)) return;
+				event.preventDefault();
+				depth.current++;
+				setDragging(true);
+				setNotice("");
+			}}
+			onDragOver={(event) => {
+				if (!hasFiles(event)) return;
+				event.preventDefault();
+				event.dataTransfer.dropEffect = "copy";
+			}}
+			onDragLeave={(event) => {
+				if (!hasFiles(event)) return;
+				depth.current = Math.max(0, depth.current - 1);
+				if (depth.current === 0) setDragging(false);
+			}}
+			onDragEnd={clearDrag}
+			onDrop={(event) => {
+				if (!hasFiles(event)) return;
+				event.preventDefault();
+				event.stopPropagation();
+				clearDrag();
+				const resolve = window.lh?.getPathForFile;
+				if (!resolve) { setNotice(BROWSER_NOTICE); return; }
+				// Directories are not file references. This check uses drag metadata,
+				// never a server request or a new filesystem capability.
+				const entries = Array.from(event.dataTransfer.items).filter((item) => item.kind === "file");
+				const paths: string[] = [];
+				let skipped = 0;
+				for (const [index, file] of Array.from(event.dataTransfer.files).entries()) {
+					try {
+						if (entries[index]?.webkitGetAsEntry?.()?.isDirectory) { skipped++; continue; }
+						const path = resolve(file);
+						quoteFilePath(path); // Same rooted-path validity rule as typed chips.
+						paths.push(path);
+					} catch { skipped++; }
+				}
+				if (paths.length === 0) {
+					setNotice("No local file paths were available. Drop existing files from your computer.");
+					return;
+				}
+				const focused = document.activeElement?.closest<HTMLElement>("[data-file-path-input]");
+				if (focused && event.currentTarget.contains(focused)) {
+					focused.dispatchEvent(new CustomEvent(INSERT_FILE_PATHS_EVENT, { detail: paths }));
+				} else if (!appendToPrimaryInput(paths.map(quoteFilePath).join(" "))) {
+					setNotice("Open a chat to attach file paths.");
+					return;
+				}
+				setNotice(skipped ? "File paths attached. Some dropped items had no available file path." : "File paths attached.");
+			}}
+		>
+			{children}
+			{dragging && (
+				<div data-testid="file-path-drop-indicator" className="pointer-events-none absolute inset-2 z-50 flex items-center justify-center rounded-xl border-2 border-dashed border-primary bg-background/85 p-6 text-center backdrop-blur-sm">
+					<div className="flex max-w-md flex-col items-center gap-3">
+						<FileSymlinkIcon className="size-8 text-primary" aria-hidden />
+						<span className="font-ui text-sm">{window.lh?.getPathForFile ? "Drop to attach file paths" : BROWSER_NOTICE}</span>
+					</div>
+				</div>
+			)}
+			{notice && <div role="status" className="absolute bottom-2 left-1/2 z-50 flex max-w-[90%] -translate-x-1/2 items-center gap-2 rounded-md border bg-card px-3 py-2 font-ui text-xs shadow-sm">
+				<span>{notice}</span>
+				<button type="button" aria-label="Dismiss attachment notice" onClick={() => setNotice("")} className="shrink-0 rounded-sm p-1 hover:bg-accent"><XIcon className="size-3" aria-hidden /></button>
+			</div>}
+		</main>
+	);
+}

components/home.tsx

@@ -13,6 +13,7 @@ import { useFieldCycle } from "@/components/field-cycle";
 import { SidebarToggle } from "@/components/sidebar";
 import { StatsBar } from "@/components/stats-bar";
 import { OPENING_PROMPT_FAILURE } from "@/components/opening-prompt";
+import { PathInput } from "@/components/path-input";
 import { SessionStarter } from "@/components/start-session";
 import type { TurnUsage } from "@/src/core";
 
@@ -64,7 +65,7 @@ export function Home({
 	/* Run end focuses the topic input (owner, 2026-10-01): the hands are on
 	 * the keyboard from the stop. Falling edge only; this surface's only
 	 * dictation target IS this textarea, so no case-split is needed. */
-	const topicInputRef = useRef<HTMLTextAreaElement>(null);
+	const topicInputRef = useRef<HTMLDivElement>(null);
 	// Tab navigates INTO the topic composer (owner, keyboard round
 	// 2026-10-06): the only text field on this surface — and home's
 	// composer is its OWN textarea, not the shared Composer component,
@@ -248,13 +249,14 @@ export function Home({
 						void start();
 					}}
 				>
-					<textarea
+					<PathInput
 						ref={topicInputRef}
 						value={topic}
-						onChange={(e) => {
-							topicRef.current = e.target.value;
-							setTopic(e.target.value);
+						onValueChange={(value) => {
+							topicRef.current = value;
+							setTopic(value);
 						}}
+						defaultDropTarget
 						onKeyDown={(e) => {
 							// Esc ends dictation (the dictate decisions: click-again or
 							// Esc) — stopPropagation claims it (keyboard wave A) so
@@ -272,7 +274,6 @@ export function Home({
 						}}
 						placeholder={mode === "practice" ? "What do you want to practice?" : "What do you want to learn?"}
 						autoFocus
-						rows={1}
 						className="field-sizing-content lh-input max-h-48 min-h-10 flex-1 resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground"
 					/>
 					{/* No tooltip on the start square — the ↵ glyph is the

components/new-session.tsx

@@ -114,7 +114,7 @@ export function DraftShell({
 	// Tab navigates INTO the composer (owner, keyboard round 2026-10-06):
 	// the only text field on this surface — the cycle's whole chain.
 	const cycleComposer = useCallback((): readonly HTMLElement[] =>
-		Array.from(document.querySelectorAll<HTMLElement>('[data-testid="composer"] textarea')),
+		Array.from(document.querySelectorAll<HTMLElement>('[data-testid="composer"] [data-file-path-input]')),
 		[]);
 	useFieldCycle(cycleComposer);
 	const dictation = useDictation({
@@ -138,7 +138,7 @@ export function DraftShell({
 	};
 	/* Run end focuses the composer (owner, 2026-10-01): the hands are on
 	 * the keyboard from the stop — falling edge of `active` only. */
-	const composerInputRef = useRef<HTMLTextAreaElement>(null);
+	const composerInputRef = useRef<HTMLDivElement>(null);
 	const dictationWasActiveRef = useRef(false);
 	useEffect(() => {
 		if (dictation.active) {

components/path-input-dom.ts

@@ -0,0 +1,245 @@
+import { parseFilePaths, quoteFilePath } from "@/src/core";
+
+/** Tokens store their complete source, not their abbreviated visual label. */
+export const PATH_SOURCE_ATTRIBUTE = "data-file-path-source";
+/** Presentation-only line box for the caret after a final model newline. */
+export const PATH_CARET_ATTRIBUTE = "data-file-path-caret";
+export type TextSelection = { anchor: number; focus: number };
+export type DOMPoint = { node: Node; offset: number };
+type Segment = { text: string; start: DOMPoint; end: DOMPoint; node?: Text; token?: Element };
+
+function childIndex(node: Node): number {
+	return Array.prototype.indexOf.call(node.parentNode!.childNodes, node);
+}
+
+/** Browser editing can leave BR/block nodes; never use innerText (layout/whitespace dependent). */
+function segments(root: HTMLElement): Segment[] {
+	const result: Segment[] = [];
+	function walk(node: Node) {
+		if (node.nodeType === 3) {
+			const text = node as Text;
+			result.push({ text: text.data, start: { node, offset: 0 }, end: { node, offset: text.length }, node: text });
+			return;
+		}
+		if (node.nodeType !== 1) return;
+		const element = node as Element;
+		if (element.hasAttribute(PATH_CARET_ATTRIBUTE)) return;
+		const raw = element.getAttribute(PATH_SOURCE_ATTRIBUTE);
+		if (raw !== null) {
+			const index = childIndex(node);
+			result.push({ text: raw, start: { node: node.parentNode!, offset: index }, end: { node: node.parentNode!, offset: index + 1 }, token: element });
+			return;
+		}
+		if (element.tagName === "BR") {
+			// Chromium's lone BR is an empty editor/paragraph placeholder.
+			if (node.parentNode?.childNodes.length === 1) return;
+			const index = childIndex(node);
+			result.push({ text: "\n", start: { node: node.parentNode!, offset: index }, end: { node: node.parentNode!, offset: index + 1 } });
+			return;
+		}
+		Array.from(node.childNodes).forEach((child, index) => {
+			const block = child.nodeType === 1 && /^(DIV|P)$/.test((child as Element).tagName);
+			const previous = node.childNodes[index - 1];
+			const previousBlock = previous?.nodeType === 1 && /^(DIV|P)$/.test((previous as Element).tagName);
+			if (index > 0 && (block || previousBlock)) {
+				result.push({ text: "\n", start: { node, offset: index }, end: { node, offset: index } });
+			}
+			walk(child);
+		});
+	}
+	walk(root);
+	return result;
+}
+
+export function readPathInput(root: HTMLElement): string {
+	return segments(root).map((part) => part.text).join("");
+}
+
+/** Map a logical UTF-16 offset to a DOM boundary, snapping a chip interior atomically. */
+export function pathInputPoint(root: HTMLElement, offset: number): DOMPoint {
+	const parts = segments(root);
+	const trailing = root.lastChild;
+	if (trailing?.nodeType === 1 && (trailing as Element).hasAttribute(PATH_CARET_ATTRIBUTE)
+		&& offset >= parts.reduce((length, part) => length + part.text.length, 0)) {
+		// A text-node endpoint after its final newline has no line box in Chromium.
+		// The boundary immediately before this BR is on the visible final line.
+		return { node: root, offset: childIndex(trailing) };
+	}
+	let remaining = Math.max(0, offset);
+	for (const part of parts) {
+		if (remaining <= part.text.length) {
+			if (part.node) return { node: part.node, offset: remaining };
+			return remaining <= part.text.length / 2 ? part.start : part.end;
+		}
+		remaining -= part.text.length;
+	}
+	return { node: root, offset: root.childNodes.length };
+}
+
+/** Works without Range: useful in DOM test environments as well as real Selection. */
+export function pathInputOffset(root: HTMLElement, node: Node, offset: number): number | null {
+	if (node !== root && !root.contains(node)) return null;
+	let total = 0;
+	for (const part of segments(root)) {
+		if (part.node === node) return total + Math.min(Math.max(0, offset), part.text.length);
+		if (part.token?.contains(node)) {
+			// A mouse/programmatic selection can end inside a noneditable label.
+			// Keep distinct interior endpoints so atomicPathRange expands copy/cut
+			// to the complete source instead of leaking the abbreviated filename.
+			let visualOffset = node.nodeType === 3 ? offset : Array.from(node.childNodes).slice(0, offset).reduce((length, child) => length + (child.textContent?.length ?? 0), 0);
+			let cursor = node;
+			while (cursor !== part.token) {
+				let sibling = cursor.previousSibling;
+				while (sibling) { visualOffset += sibling.textContent?.length ?? 0; sibling = sibling.previousSibling; }
+				cursor = cursor.parentNode!;
+			}
+			const visualLength = part.token.textContent?.length ?? 0;
+			return total + (visualLength ? Math.round(Math.min(visualLength, visualOffset) / visualLength * part.text.length) : 0);
+		}
+		if (part.start.node === node && part.start.offset >= offset) return total;
+		if (part.end.node === node && part.end.offset <= offset) {
+			total += part.text.length;
+			continue;
+		}
+		// A boundary in an ancestor is before/after every descendant segment.
+		let ancestor: Node = part.node ?? part.token ?? part.start.node;
+		while (ancestor.parentNode && ancestor.parentNode !== node) ancestor = ancestor.parentNode;
+		if (ancestor.parentNode === node && childIndex(ancestor) >= offset) return total;
+		total += part.text.length;
+	}
+	return total;
+}
+
+export function readPathSelection(root: HTMLElement): TextSelection | null {
+	const selection = root.ownerDocument.getSelection?.();
+	if (!selection?.anchorNode || !selection.focusNode) return null;
+	const anchor = pathInputOffset(root, selection.anchorNode, selection.anchorOffset);
+	const focus = pathInputOffset(root, selection.focusNode, selection.focusOffset);
+	return anchor === null || focus === null ? null : { anchor, focus };
+}
+
+export function restorePathSelection(root: HTMLElement, selection: TextSelection): void {
+	const browserSelection = root.ownerDocument.getSelection?.();
+	if (!browserSelection) return;
+	const anchor = pathInputPoint(root, selection.anchor);
+	const focus = pathInputPoint(root, selection.focus);
+	browserSelection.setBaseAndExtent(anchor.node, anchor.offset, focus.node, focus.offset);
+}
+
+/** Returns portal hosts. React owns only their visual contents, never the editable tree. */
+export function renderPathInput(root: HTMLElement, value: string): Array<{ host: HTMLElement; path: string }> {
+	const document = root.ownerDocument;
+	const fragment = document.createDocumentFragment();
+	const chips: Array<{ host: HTMLElement; path: string }> = [];
+	for (const part of parseFilePaths(value)) {
+		if (part.kind === "text") {
+			fragment.append(document.createTextNode(part.text));
+		} else {
+			const host = document.createElement("span");
+			host.contentEditable = "false";
+			host.setAttribute("contenteditable", "false");
+			host.setAttribute(PATH_SOURCE_ATTRIBUTE, part.text);
+			fragment.append(host);
+			chips.push({ host, path: part.path });
+		}
+	}
+	// Empty boundary text nodes allow a caret immediately before/after an atomic chip.
+	if (!fragment.firstChild || fragment.firstChild.nodeType !== 3) fragment.prepend(document.createTextNode(""));
+	if (fragment.lastChild?.nodeType !== 3) fragment.append(document.createTextNode(""));
+	if (value.endsWith("\n")) {
+		// pre-wrap alone collapses the final empty line. This BR supplies its
+		// height/caret without adding a second newline to the stored source.
+		const caret = document.createElement("br");
+		caret.setAttribute(PATH_CARET_ATTRIBUTE, "");
+		caret.setAttribute("aria-hidden", "true");
+		fragment.append(caret);
+	}
+	root.replaceChildren(fragment);
+	root.dataset.empty = value.length === 0 ? "true" : "false";
+	return chips;
+}
+
+export function clampPathSelection(value: string, selection: TextSelection): TextSelection {
+	const clamp = (offset: number) => Math.min(value.length, Math.max(0, offset));
+	return { anchor: clamp(selection.anchor), focus: clamp(selection.focus) };
+}
+
+/** A selection intersecting any part of a chip edits/copies that complete source. */
+export function atomicPathRange(value: string, selection: TextSelection): { start: number; end: number } {
+	const clamped = clampPathSelection(value, selection);
+	let start = Math.min(clamped.anchor, clamped.focus);
+	let end = Math.max(clamped.anchor, clamped.focus);
+	for (const part of parseFilePaths(value)) {
+		if (part.kind !== "path") continue;
+		if (start > part.start && start < part.end) start = part.start;
+		if (end > part.start && end < part.end) end = part.end;
+	}
+	return { start, end };
+}
+
+export function replacePathSelection(value: string, selection: TextSelection, text: string) {
+	const { start, end } = atomicPathRange(value, selection);
+	return { value: value.slice(0, start) + text + value.slice(end), selection: { anchor: start + text.length, focus: start + text.length } };
+}
+
+export function insertFilePaths(value: string, selection: TextSelection, paths: string[]) {
+	const { start, end } = atomicPathRange(value, selection);
+	const text = paths.map(quoteFilePath).join(" ");
+	if (!text) return { value, selection };
+	const before = start > 0 && !/\s/.test(value[start - 1]!) ? " " : "";
+	const after = end < value.length && !/\s/.test(value[end]!) ? " " : "";
+	return replacePathSelection(value, selection, before + text + after);
+}
+
+export function adjacentPathRange(value: string, selection: TextSelection, direction: "backward" | "forward"): TextSelection | null {
+	if (selection.anchor !== selection.focus) return selection;
+	const caret = selection.focus;
+	for (const part of parseFilePaths(value)) {
+		if (part.kind === "path" && (direction === "backward" ? caret > part.start && caret <= part.end : caret >= part.start && caret < part.end)) {
+			return { anchor: part.start, focus: part.end };
+		}
+	}
+	return null;
+}
+
+export type PathEditSnapshot = { value: string; selection: TextSelection };
+
+/** Match the text input value sanitization algorithm: remove CR/LF, not spaces. */
+export function normalizePathInputValue(value: string, singleLine: boolean): string {
+	return singleLine ? value.replace(/[\r\n]/g, "") : value;
+}
+
+export function normalizePathEdit(snapshot: PathEditSnapshot, singleLine: boolean): PathEditSnapshot {
+	if (!singleLine) return snapshot;
+	const selection = clampPathSelection(snapshot.value, snapshot.selection);
+	return {
+		value: normalizePathInputValue(snapshot.value, true),
+		selection: {
+			anchor: normalizePathInputValue(snapshot.value.slice(0, selection.anchor), true).length,
+			focus: normalizePathInputValue(snapshot.value.slice(0, selection.focus), true).length,
+		},
+	};
+}
+
+/** Independent of the browser's DOM undo stack (normalization replaces native nodes). */
+export class PathInputHistory {
+	private undoStack: PathEditSnapshot[] = [];
+	private redoStack: PathEditSnapshot[] = [];
+	push(snapshot: PathEditSnapshot) {
+		this.undoStack.push({ value: snapshot.value, selection: { ...snapshot.selection } });
+		this.redoStack = [];
+	}
+	reset() { this.undoStack = []; this.redoStack = []; }
+	undo(current: PathEditSnapshot): PathEditSnapshot | null {
+		const previous = this.undoStack.pop();
+		if (!previous) return null;
+		this.redoStack.push(current);
+		return previous;
+	}
+	redo(current: PathEditSnapshot): PathEditSnapshot | null {
+		const next = this.redoStack.pop();
+		if (!next) return null;
+		this.undoStack.push(current);
+		return next;
+	}
+}

components/path-input.tsx

@@ -0,0 +1,291 @@
+"use client";
+
+import * as React from "react";
+import { createPortal } from "react-dom";
+import { FilePathChip } from "./file-path-chip";
+import { cn } from "../lib/utils";
+import {
+	adjacentPathRange, atomicPathRange, clampPathSelection, insertFilePaths,
+	normalizePathEdit, normalizePathInputValue, PathInputHistory, readPathInput, readPathSelection, renderPathInput,
+	replacePathSelection, restorePathSelection,
+	type PathEditSnapshot, type TextSelection,
+} from "./path-input-dom";
+
+export const INSERT_FILE_PATHS_EVENT = "lh:insert-file-paths";
+export type PathInputProps = Omit<React.HTMLAttributes<HTMLDivElement>, "children" | "dangerouslySetInnerHTML" | "defaultValue" | "onChange"> & {
+	value: string;
+	onValueChange: (value: string) => void;
+	placeholder?: string;
+	autoFocus?: boolean;
+	defaultDropTarget?: boolean;
+	/** Native text-input semantics: strip CR/LF and leave Enter to the caller. */
+	singleLine?: boolean;
+};
+
+type ChipHost = { host: HTMLElement; path: string };
+type Controller = {
+	external: (value: string) => void;
+	remember: () => void;
+};
+
+/**
+ * A controlled plaintext editor. Only the source string is state; chips are atomic
+ * views of it. React never reconciles the editable DOM after a native mutation.
+ */
+export const PathInput = React.forwardRef<HTMLDivElement, PathInputProps>(function PathInput({
+	value, onValueChange, placeholder, autoFocus, defaultDropTarget = false, singleLine = false, className,
+	onKeyDown, onFocus, onBlur, onInput, onPaste, onCopy, onCut,
+	onCompositionStart, onCompositionEnd, ...props
+}, forwardedRef) {
+	const rootRef = React.useRef<HTMLDivElement>(null);
+	const controllerRef = React.useRef<Controller | null>(null);
+	const callbacks = React.useRef({ onValueChange, singleLine });
+	const composing = React.useRef(false);
+	const [chips, setChips] = React.useState<ChipHost[]>([]);
+	// Keep this text child immutable: SSR/hydration gets the complete draft,
+	// while subsequent React renders leave the browser-owned editable DOM alone.
+	const initial = React.useRef({ value: normalizePathInputValue(value, singleLine), autoFocus, singleLine });
+
+	React.useImperativeHandle(forwardedRef, () => rootRef.current!, []);
+	React.useLayoutEffect(() => { callbacks.current = { onValueChange, singleLine }; }, [onValueChange, singleLine]);
+
+	React.useLayoutEffect(() => {
+		const root = rootRef.current!;
+		const document = root.ownerDocument;
+		let current = normalizePathInputValue(initial.current.value, initial.current.singleLine);
+		let saved: TextSelection = { anchor: current.length, focus: current.length };
+		let beforeEdit: PathEditSnapshot | null = null;
+		let compositionStart: PathEditSnapshot | null = null;
+		let pendingExternal: string | null = null;
+		let pendingPaths: string[] = [];
+		let pendingPaste: string[] = [];
+		let mounted = true;
+		const history = new PathInputHistory();
+
+		function remember() {
+			if (document.activeElement !== root) return;
+			const selection = readPathSelection(root);
+			if (selection) saved = selection;
+		}
+		function snapshot(): PathEditSnapshot {
+			return { value: current, selection: { ...saved } };
+		}
+		function paint(selection: TextSelection, restore: boolean) {
+			setChips(renderPathInput(root, current));
+			saved = clampPathSelection(current, selection);
+			if (restore) restorePathSelection(root, saved);
+		}
+		function change(next: PathEditSnapshot, record = true, before = snapshot(), notify = true) {
+			next = normalizePathEdit(next, callbacks.current.singleLine);
+			if (next.value === current) { paint(next.selection, document.activeElement === root); return; }
+			if (record) history.push(before);
+			current = next.value;
+			paint(next.selection, document.activeElement === root);
+			if (notify) callbacks.current.onValueChange(current);
+		}
+		function replace(text: string) {
+			remember();
+			change(replacePathSelection(current, saved, text));
+		}
+		function travel(direction: "undo" | "redo") {
+			remember();
+			const next = history[direction](snapshot());
+			if (next) change(next, false);
+		}
+		function stage(paths: string[]) {
+			if (composing.current) { pendingPaths.push(...paths); return; }
+			remember();
+			// Global drop may have moved focus: saved selection is still authoritative.
+			let next: PathEditSnapshot;
+			try { next = insertFilePaths(current, saved, paths); }
+			catch { return; } // Invalid event payloads never mutate learner text.
+			change(next);
+			root.focus();
+			restorePathSelection(root, saved);
+		}
+		function insertEvent(event: Event) {
+			const paths: unknown = (event as CustomEvent<unknown>).detail;
+			if (Array.isArray(paths) && paths.every((path) => typeof path === "string")) stage(paths);
+		}
+		function beforeInput(event: InputEvent) {
+			if (composing.current || event.isComposing) return;
+			remember();
+			beforeEdit = snapshot();
+			if (event.inputType === "historyUndo" || event.inputType === "historyRedo") {
+				event.preventDefault();
+				travel(event.inputType === "historyUndo" ? "undo" : "redo");
+			} else if (event.inputType === "insertParagraph" || event.inputType === "insertLineBreak") {
+				event.preventDefault();
+				if (!callbacks.current.singleLine) replace("\n");
+			} else if (event.inputType.startsWith("format") || event.inputType === "insertHTML") {
+				event.preventDefault();
+			} else if (event.inputType === "deleteByCut") {
+				// The cut handler owns both the full-source clipboard and deletion.
+				// Never perform a second deletion if a browser also sends beforeinput.
+				event.preventDefault();
+			} else if (event.inputType.startsWith("delete")) {
+				const range = adjacentPathRange(current, saved, event.inputType.includes("Backward") ? "backward" : "forward");
+				if (range) {
+					event.preventDefault();
+					change(replacePathSelection(current, range, ""));
+				}
+			}
+		}
+		function input() {
+			if (composing.current) {
+				root.dataset.empty = normalizePathInputValue(readPathInput(root), callbacks.current.singleLine).length === 0 ? "true" : "false";
+				return;
+			}
+			const nextValue = readPathInput(root);
+			const selection = readPathSelection(root) ?? saved;
+			const previous = beforeEdit ?? snapshot();
+			beforeEdit = null;
+			change({ value: nextValue, selection }, true, previous);
+		}
+		function keyDown(event: KeyboardEvent) {
+			if (composing.current || event.isComposing || event.keyCode === 229) return;
+			// Shift+Delete is native Cut on Windows/Linux, not forward deletion.
+			// Let the browser dispatch cut so our clipboard handler can own it.
+			if (event.key === "Delete" && event.shiftKey && !event.ctrlKey && !event.metaKey && !event.altKey) return;
+			remember();
+			if ((event.metaKey || event.ctrlKey) && !event.altKey && (event.key.toLowerCase() === "z" || event.key.toLowerCase() === "y")) {
+				event.preventDefault();
+				travel(event.key.toLowerCase() === "y" || event.shiftKey ? "redo" : "undo");
+			} else if (event.key === "Backspace" || event.key === "Delete") {
+				const range = adjacentPathRange(current, saved, event.key === "Backspace" ? "backward" : "forward");
+				if (range) {
+					event.preventDefault();
+					change(replacePathSelection(current, range, ""));
+				}
+			}
+		}
+		function paste(event: ClipboardEvent) {
+			if (event.defaultPrevented) return;
+			event.preventDefault();
+			const text = event.clipboardData?.getData("text/plain") ?? "";
+			// Image/file/HTML-only clipboard contents are not text replacement.
+			if (text === "") return;
+			if (composing.current) pendingPaste.push(text);
+			else replace(text);
+		}
+		function copy(event: ClipboardEvent) {
+			if (event.defaultPrevented) return;
+			remember();
+			if (saved.anchor === saved.focus || !event.clipboardData) return;
+			const { start, end } = atomicPathRange(current, saved);
+			event.clipboardData.setData("text/plain", current.slice(start, end));
+			event.preventDefault();
+			if (event.type === "cut" && !composing.current) change(replacePathSelection(current, saved, ""));
+		}
+		function startComposition() {
+			remember();
+			composing.current = true;
+			compositionStart = snapshot();
+		}
+		function endComposition() {
+			// Some browsers send the final input immediately AFTER compositionend.
+			queueMicrotask(() => {
+				if (!mounted) return;
+				let nextValue = readPathInput(root);
+				let selection = readPathSelection(root) ?? saved;
+				const previous = compositionStart ?? snapshot();
+				const reset = pendingExternal !== null && !pendingExternal.startsWith(previous.value);
+				const nativeChanged = normalizePathInputValue(nextValue, callbacks.current.singleLine) !== current;
+				const notify = pendingExternal === null || (!reset && nativeChanged);
+				if (pendingExternal !== null) {
+					if (pendingExternal.startsWith(previous.value)) {
+						nextValue += pendingExternal.slice(previous.value.length);
+					} else {
+						nextValue = pendingExternal;
+						selection = clampPathSelection(nextValue, selection);
+					}
+				}
+				pendingExternal = null;
+				compositionStart = null;
+				beforeEdit = null;
+				composing.current = false;
+				if (reset) history.reset();
+				change({ value: nextValue, selection }, !reset, previous, notify);
+				if (pendingPaste.length) { const text = pendingPaste.join(""); pendingPaste = []; replace(text); }
+				if (pendingPaths.length) { const paths = pendingPaths; pendingPaths = []; stage(paths); }
+			});
+		}
+		controllerRef.current = {
+			remember,
+			external(next) {
+				next = normalizePathInputValue(next, callbacks.current.singleLine);
+				if (composing.current) { pendingExternal = next; return; }
+				if (next === current) return;
+				remember();
+				const previous = snapshot();
+				// Dictation appends are undoable; a controlled reset starts fresh history.
+				if (next && next.startsWith(current)) history.push(previous);
+				else history.reset();
+				const selection = saved.anchor === current.length && saved.focus === current.length
+					? { anchor: next.length, focus: next.length } : clampPathSelection(next, saved);
+				current = next;
+				paint(selection, document.activeElement === root);
+			},
+		};
+		paint(saved, false);
+		if (initial.current.autoFocus) { root.focus(); restorePathSelection(root, saved); }
+		root.addEventListener(INSERT_FILE_PATHS_EVENT, insertEvent);
+		root.addEventListener("beforeinput", beforeInput);
+		root.addEventListener("input", input);
+		root.addEventListener("keydown", keyDown);
+		root.addEventListener("paste", paste);
+		root.addEventListener("copy", copy);
+		root.addEventListener("cut", copy);
+		root.addEventListener("compositionstart", startComposition);
+		root.addEventListener("compositionend", endComposition);
+		document.addEventListener("selectionchange", remember);
+		return () => {
+			mounted = false;
+			composing.current = false;
+			controllerRef.current = null;
+			root.removeEventListener(INSERT_FILE_PATHS_EVENT, insertEvent);
+			root.removeEventListener("beforeinput", beforeInput);
+			root.removeEventListener("input", input);
+			root.removeEventListener("keydown", keyDown);
+			root.removeEventListener("paste", paste);
+			root.removeEventListener("copy", copy);
+			root.removeEventListener("cut", copy);
+			root.removeEventListener("compositionstart", startComposition);
+			root.removeEventListener("compositionend", endComposition);
+			document.removeEventListener("selectionchange", remember);
+		};
+	}, []);
+
+	React.useLayoutEffect(() => { controllerRef.current?.external(value); }, [value, singleLine]);
+
+	return <>
+		<div
+			{...props}
+			ref={rootRef}
+			role="textbox"
+			aria-label={props["aria-label"] ?? placeholder}
+			aria-multiline={singleLine ? "false" : "true"}
+			aria-placeholder={placeholder}
+			contentEditable
+			suppressContentEditableWarning
+			data-file-path-input=""
+			data-empty={initial.current.value.length === 0 ? "true" : "false"}
+			data-file-path-default={defaultDropTarget ? "" : undefined}
+			data-placeholder={placeholder}
+			className={cn("block w-full min-w-0 outline-none data-[empty=true]:before:pointer-events-none data-[empty=true]:before:text-muted-foreground data-[empty=true]:before:content-[attr(data-placeholder)]", singleLine ? "whitespace-pre break-normal overflow-x-auto overflow-y-hidden" : "whitespace-pre-wrap break-words overflow-y-auto", className)}
+			onKeyDown={(event) => {
+				if (composing.current || event.nativeEvent.isComposing || event.keyCode === 229) { event.stopPropagation(); return; }
+				onKeyDown?.(event);
+			}}
+			onFocus={(event) => { controllerRef.current?.remember(); onFocus?.(event); }}
+			onBlur={(event) => { controllerRef.current?.remember(); onBlur?.(event); }}
+			onInput={onInput}
+			onPaste={onPaste}
+			onCopy={onCopy}
+			onCut={onCut}
+			onCompositionStart={onCompositionStart}
+			onCompositionEnd={onCompositionEnd}
+		>{initial.current.value}</div>
+		{chips.map(({ host, path }) => createPortal(<FilePathChip path={path} contentEditable={false} />, host))}
+	</>;
+});

components/practice-dock.tsx

@@ -6,6 +6,7 @@ import { ToolContentResponse } from "@/components/ai-elements/message";
 import { Button } from "@/components/ui/button";
 import { joinDictation, useDictationTarget } from "@/components/dictation";
 import { useEnterSubmits } from "@/components/enter-submits";
+import { PathInput } from "@/components/path-input";
 import { cn } from "@/lib/utils";
 
 /**
@@ -121,11 +122,11 @@ export function PracticeDock({ problemCallId, input, expanded, onExpand, onSubmi
 				<div className="px-2.5 pt-2 text-xs font-medium uppercase tracking-wide text-muted-foreground">
 					YOUR THINKING
 				</div>
-				<textarea
+				<PathInput
 					value={thinking}
-					onChange={(e) => {
-						thinkingRef.current = e.target.value;
-						setThinking(e.target.value);
+					onValueChange={(value) => {
+						thinkingRef.current = value;
+						setThinking(value);
 					}}
 					onKeyDown={(e) => {
 						// Esc ends dictation — stopPropagation claims it (the
@@ -144,7 +145,6 @@ export function PracticeDock({ problemCallId, input, expanded, onExpand, onSubmi
 						}
 					}}
 					placeholder="Work here, think out loud."
-					rows={4}
 					className={cn(
 						"field-sizing-content lh-input max-h-64 min-h-16 w-full resize-none bg-transparent px-2.5 pb-2 outline-none placeholder:text-muted-foreground",
 					)}

components/question-dock.tsx

@@ -5,6 +5,7 @@ import { ArrowDownIcon, ChevronRightIcon, PlayIcon } from "lucide-react";
 import { Button } from "@/components/ui/button";
 import { finishDictation, isDictationActive, joinDictation, useDictationTarget } from "@/components/dictation";
 import { useEnterSubmits } from "@/components/enter-submits";
+import { PathInput } from "@/components/path-input";
 import { ToolContentResponse } from "@/components/ai-elements/message";
 import { cn } from "@/lib/utils";
 import {
@@ -439,8 +440,8 @@ function QuestionDockForm({
 	   expanded — collapsed, the bar's native Enter expands it. */
 	const [kbdIdx, setKbdIdx] = useState<number | null>(null);
 	const rootRef = useRef<HTMLDivElement>(null);
-	const otherInputRef = useRef<HTMLInputElement>(null);
-	const thinkingRef = useRef<HTMLTextAreaElement>(null);
+	const otherInputRef = useRef<HTMLDivElement>(null);
+	const thinkingRef = useRef<HTMLDivElement>(null);
 	// One row past the options is the trailing row: quiz → don't-know,
 	// ask → Other (a question never has both). Text mode (ask/explain)
 	// has no rows — the composer IS the answer surface.
@@ -473,7 +474,7 @@ function QuestionDockForm({
 	const focusRow = (idx: number) => {
 		const row = rootRef.current?.querySelector(`[data-kbdrow="${idx}"]`) as HTMLElement | null;
 		if (!row) return;
-		const el = (row.querySelector("input") as HTMLElement | null) ?? row;
+		const el = (row.querySelector("input, [data-file-path-input]") as HTMLElement | null) ?? row;
 		el.focus();
 	};
 
@@ -696,11 +697,12 @@ function QuestionDockForm({
 										</span>
 									)}
 								</span>
-								<input
+								<PathInput
 									ref={otherInputRef}
+									singleLine
 									value={other}
-									onChange={(e) => {
-										setOther(e.target.value);
+									onValueChange={(value) => {
+										setOther(value);
 										// Typing selects the row — displacing in
 										// single-select, alongside the siblings in multi.
 										setSel((prev) => (prev.otherSelected ? prev : toggleOther(selectMode, prev)));
@@ -851,11 +853,11 @@ function QuestionDockForm({
 						{qd.mode === "text" ? "Your answer" : "YOUR THINKING"}
 					</div>
 					{qd.mode === "text" ? (
-						<textarea
+						<PathInput
 							value={text}
-							onChange={(e) => {
-								answerTextRef.current = e.target.value;
-								setText(e.target.value);
+							onValueChange={(value) => {
+								answerTextRef.current = value;
+								setText(value);
 							}}
 							onKeyDown={(e) => {
 								// Esc ends dictation (the dictate decisions: click-again
@@ -875,16 +877,15 @@ function QuestionDockForm({
 								}
 							}}
 							placeholder="Type your answer…"
-							rows={1}
 							className="field-sizing-content lh-input max-h-48 min-h-10 w-full resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground"
 						/>
 					) : (
-						<textarea
+						<PathInput
 							ref={thinkingRef}
 							value={thinking}
-							onChange={(e) => {
-								thinkingTextRef.current = e.target.value;
-								setThinking(e.target.value);
+							onValueChange={(value) => {
+								thinkingTextRef.current = value;
+								setThinking(value);
 							}}
 							onKeyDown={(e) => {
 								// Esc ends dictation (the dictate decisions: click-again
@@ -905,7 +906,6 @@ function QuestionDockForm({
 								}
 							}}
 							placeholder="Why this answer? Whatever comes to mind."
-							rows={1}
 							className={cn(
 								"field-sizing-content lh-input max-h-48 w-full resize-none bg-transparent px-2.5 py-2 outline-none placeholder:text-muted-foreground/70",
 								// Phase-scaled prominence: teaching invites depth,

components/reading-thinking.tsx

@@ -2,6 +2,7 @@
 
 import { useCallback } from "react";
 import { joinDictation, useDictationTarget } from "@/components/dictation";
+import { PathInput } from "@/components/path-input";
 
 /**
  * The reading-thinking field (owner design 2026-10-03, "two questions per
@@ -54,9 +55,9 @@ export function ReadingThinkingField({
 			<div className="pb-1 text-xs font-medium uppercase tracking-wide text-muted-foreground">
 				Thinking while reading
 			</div>
-			<textarea
+			<PathInput
 				value={value}
-				onChange={(e) => onChange(e.target.value)}
+				onValueChange={onChange}
 				/* py-0.5 (owner round, 2026-10-07): the scrollbar fix. Source
 				   Sans 3's font box is 22px at 16px; lh-input's 1.25 leading
 				   gives a 20px line box — the content area sticks 1px below the
@@ -95,7 +96,6 @@ export function ReadingThinkingField({
 					}
 				}}
 				placeholder="Whatever comes to mind as you read."
-				rows={1}
 				className="field-sizing-content lh-input max-h-40 w-full resize-none bg-transparent py-0.5 outline-none placeholder:text-muted-foreground/70"
 			/>
 		</div>

components/session-find-dom.ts

@@ -4,7 +4,7 @@ import { findSessionTextMatches } from "@/src/core";
  * hidden/unmounted sections do not. Never walk embedded documents or drafts.
  * Do NOT exclude aria-hidden globally: KaTeX's VISIBLE HTML uses it too. */
 const EXCLUDED = [
-	"script", "style", "noscript", "textarea", "input", "select", "iframe", "canvas",
+	"script", "style", "noscript", "textarea", "input", "select", "iframe", "canvas", '[contenteditable="true"]',
 	"title", "defs", "metadata", "desc", ".katex-mathml", ".sr-only", "[hidden]",
 	"[data-session-find-exclude]", "[data-lh-menu]", '[role="menu"]', '[role="dialog"]', '[role="tooltip"]',
 ].join(",");

components/sidebar.tsx

@@ -50,6 +50,7 @@ const STORAGE_KEY = "lh:sidebar-open";
  */
 import type { ChatGPTControlBridge, NativeSubscriptionControlBridge } from "@/src/core";
 import type { UpdateState } from "@/components/settings/update-settings.tsx";
+import { FilePathDropZone } from "@/components/file-path-drop-zone";
 const SIDEBAR_AUTOCLOSE = 928;
 
 // Module scope, guarded for SSR (the server has no navigator).
@@ -61,6 +62,8 @@ declare global {
 		lh?: {
 			/** Read-only host OS; determines the native-control gutter. */
 			platform?: string;
+			/** Resolve an OS-backed File without copying/uploading its contents. */
+			getPathForFile?: (file: File) => string;
 			/** External Next desktop-dev uses the server's web connections. */
 			subscriptionTransport?: "desktop" | "web";
 			openSubscriptionBrowser?: (action: string) => Promise<void>;
@@ -944,7 +947,7 @@ export function AppShell({ children }: { children: React.ReactNode }) {
 	return (
 		<SettingsDialogProvider>
 			<SessionsSidebar />
-			<main className="min-w-0 flex-1">{children}</main>
+			<FilePathDropZone className="relative min-w-0 flex-1">{children}</FilePathDropZone>
 			{/* The single document-level keydown listener (keyboard wave A) —
 			    after the content in the tree, but it's window-level so order only
 			    matters for the events it dispatches, never for DOM priority. */}

components/thinking-block.tsx

@@ -4,6 +4,7 @@ import { useEffect, useRef, useState } from "react";
 import { ChevronDownIcon } from "lucide-react";
 import { blurAfterPointerClick } from "@/components/focus-hygiene";
 import { cn } from "@/lib/utils";
+import { PathText } from "@/components/file-path-chip";
 
 /** The unified user-thinking row (owner round, 2026-10-05): ONE visual
  *  language for every surface where the learner's own thinking renders —
@@ -127,7 +128,7 @@ export function ThinkingBlock({
 				<ChevronDownIcon className={cn("size-4 shrink-0 transition-transform", open ? "rotate-180" : "rotate-0")} />
 			</button>
 			{open && (
-				<span className="lh-prose mt-1.5 block whitespace-pre-wrap text-[15px] italic text-foreground/50">{text}</span>
+				<span className="lh-prose mt-1.5 block whitespace-pre-wrap text-[15px] italic text-foreground/50"><PathText text={text} /></span>
 			)}
 		</div>
 	);

electron/preload.cjs

@@ -29,7 +29,7 @@
  *
  * Channel names are mirrored in electron/main.cjs — keep them in sync.
  */
-const { contextBridge, ipcRenderer } = require("electron");
+const { contextBridge, ipcRenderer, webUtils } = require("electron");
 
 let openSettingsListener = null;
 let pendingOpenSettings = null;
@@ -40,6 +40,9 @@ ipcRenderer.on("lh:open-settings", (_event, section) => {
 
 contextBridge.exposeInMainWorld("lh", {
 	platform: process.platform,
+	// Resolve only a renderer-supplied, OS-backed File. No filesystem API,
+	// uploads, copies, or DOM File IPC to main; sandbox/isolation stay on.
+	getPathForFile: (file) => webUtils.getPathForFile(file),
 	...(process.argv?.includes("--lh-web-subscriptions") ? {
 		subscriptionTransport: "web",
 		openSubscriptionBrowser: (action) => ipcRenderer.invoke("lh:subscriptions:web-browser", action),

scripts/smoke-file-paths.mjs

@@ -0,0 +1,424 @@
+/** Offline synthetic UI + actual Electron preload smoke. No providers/accounts.
+ * Run: node scripts/smoke-file-paths.mjs
+ * App/profile/auth/OS-backed fixture files are temporary; only this script's
+ * processes are stopped. Browser requests outside the owned origin are blocked.
+ */
+import assert from "node:assert/strict";
+import { spawn } from "node:child_process";
+import { once } from "node:events";
+import fs from "node:fs";
+import net from "node:net";
+import { createRequire } from "node:module";
+import os from "node:os";
+import path from "node:path";
+import puppeteer from "puppeteer-core";
+
+const root = path.resolve(import.meta.dirname, "..");
+const home = fs.mkdtempSync(path.join(os.tmpdir(), "lh-file-paths-"));
+const require = createRequire(import.meta.url);
+const checks = [];
+const errors = [];
+const visualFailures = [];
+const coverageFailures = [];
+const posts = [];
+const blocked = [];
+const networkFailures = [];
+const consoleErrors = [];
+const children = [];
+const browsers = [];
+const screenshots = [];
+let serverLogs = "";
+let electronLogs = "";
+let page;
+let origin;
+let shuttingDown = false;
+const fixtureCatalog = (() => {
+	const model = { id: "synthetic", name: "Synthetic (no calls)", provider: "fixture", input: ["text"], reasoning: false, supportedLevels: ["off"], cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 }, contextWindow: 8192, maxTokens: 1024 };
+	const slot = { model: { provider: model.provider, id: model.id }, thinkingLevel: "off" };
+	return { models: [model], providers: [{ id: "fixture", label: "Fixture", keyPresent: true }], defaults: null, slots: { strong: slot, cheap: slot, vision: slot }, rolePins: {} };
+})();
+async function freePort() {
+	const listener = net.createServer();
+	listener.listen(0, "127.0.0.1");
+	await once(listener, "listening");
+	const port = listener.address().port;
+	await new Promise(resolve => listener.close(resolve));
+	return port;
+}
+async function stop(child) {
+	if (!child || child.exitCode !== null || child.signalCode !== null) return;
+	const exited = once(child, "exit");
+	child.kill("SIGTERM");
+	const timer = setTimeout(() => child.kill("SIGKILL"), 5000); timer.unref();
+	await exited; clearTimeout(timer);
+}
+async function startup(child, getLogs, marker, timeout = 90000) {
+	await new Promise((resolve, reject) => {
+		const timer = setTimeout(() => finish(new Error(`Startup timed out: ${getLogs()}`)), timeout);
+		const inspect = () => { if (marker.test(getLogs())) finish(); };
+		const exited = code => finish(new Error(`Process exited ${code}: ${getLogs()}`));
+		function finish(error) {
+			clearTimeout(timer); child.stdout.off("data", inspect); child.stderr.off("data", inspect); child.off("exit", exited);
+			if (error) reject(error); else resolve();
+		}
+		child.stdout.on("data", inspect); child.stderr.on("data", inspect); child.once("exit", exited); inspect();
+	});
+}
+async function instrument(target) {
+	target.setDefaultTimeout(20000);
+	target.on("pageerror", error => { if (!shuttingDown) errors.push(error.message); });
+	target.on("requestfailed", request => { if (!shuttingDown) networkFailures.push({ url: request.url(), error: request.failure()?.errorText }); });
+	target.on("console", message => { if (message.type() === "error") consoleErrors.push(message.text()); });
+	await target.setRequestInterception(true);
+	target.on("request", async request => {
+		try {
+			const url = new URL(request.url());
+			if (url.protocol === "data:" || url.protocol === "about:") return await request.continue();
+			if (url.origin !== origin) { blocked.push(request.url()); return await request.abort(); }
+			const respond = body => request.respond({ status: 200, contentType: "application/json", body: JSON.stringify(body) });
+			if (url.pathname === "/api/models") return await respond(fixtureCatalog);
+			if (url.pathname === "/api/events") return await request.respond({ status: 204 });
+			// Never forward agent, answer or import requests, even if a UI bug
+			// submits while dropping. Record their complete synthetic bodies.
+			if (request.method() === "POST" && (/^\/api\/(chat|answer)(\/|$)/.test(url.pathname) || /\/(answer|import|turn|retry)(\/|$)/.test(url.pathname))) {
+				posts.push({ pathname: url.pathname, body: JSON.parse(request.postData() || "{}") });
+				return await request.respond({ status: 503, contentType: "application/json", body: JSON.stringify({ code: "models_not_configured", missing: ["strong"] }) });
+			}
+			if (/^\/api\/chats\/[^/]+\/stream$/.test(url.pathname)) return await request.respond({ status: 204 });
+			return await request.continue();
+		} catch (error) {
+			if (!shuttingDown && !/Target closed|Session closed|Invalid InterceptionId|already handled/.test(String(error))) errors.push(String(error));
+		}
+	});
+}
+const inputSelector = '[data-file-path-input]';
+async function open(target, route) {
+	await target.goto(origin + route, { waitUntil: "domcontentloaded", timeout: 120000 });
+	await target.waitForSelector(inputSelector);
+	await target.waitForFunction(() => !document.querySelector('[data-testid="setup-cta"], [data-testid="setup-cta-keys"]'));
+	await target.waitForFunction(() => document.querySelector('[data-testid="file-path-drop-zone"]'));
+}
+async function read(target, selector = inputSelector) {
+	return target.$eval(selector, element => [...element.childNodes].map(node => node.nodeType === 1 ? node.getAttribute("data-file-path-source") ?? node.textContent : node.textContent).join(""));
+}
+async function expectValue(target, expected, selector = inputSelector) {
+	await target.waitForFunction((selector, expected) => {
+		const element = document.querySelector(selector);
+		return element && [...element.childNodes].map(node => node.nodeType === 1 ? node.getAttribute("data-file-path-source") ?? node.textContent : node.textContent).join("") === expected;
+	}, {}, selector, expected);
+}
+async function fill(target, value, selector = inputSelector) {
+	await target.$eval(selector, (element, value) => {
+		element.focus(); element.textContent = value;
+		const selection = document.getSelection(); selection.collapse(element, element.childNodes.length);
+		element.dispatchEvent(new InputEvent("input", { bubbles: true, inputType: "insertText" }));
+	}, value);
+	await expectValue(target, value, selector);
+}
+async function caret(target, offset, selector = inputSelector) {
+	await target.$eval(selector, (element, offset) => {
+		element.focus(); let rest = offset;
+		for (const node of element.childNodes) {
+			const source = node.nodeType === 1 ? node.getAttribute("data-file-path-source") : null;
+			const length = source?.length ?? node.textContent.length;
+			if (rest <= length) {
+				if (source !== null) {
+					const index = [...element.childNodes].indexOf(node);
+					document.getSelection().collapse(element, index + (rest > 0 ? 1 : 0));
+				} else document.getSelection().collapse(node, rest);
+				document.dispatchEvent(new Event("selectionchange")); return;
+			}
+			rest -= length;
+		}
+		document.getSelection().collapse(element, element.childNodes.length);
+		document.dispatchEvent(new Event("selectionchange"));
+	}, offset);
+}
+async function shortcut(target, key, shift = false) {
+	await target.keyboard.down("Meta"); if (shift) await target.keyboard.down("Shift");
+	await target.keyboard.press(key);
+	if (shift) await target.keyboard.up("Shift"); await target.keyboard.up("Meta");
+}
+async function clipboardCommand(target, command, key, modifiers = 4) {
+	// Headless Chromium does not run the macOS menu accelerator for Meta+C/V.
+	// CDP's native edit command triggers the real browser clipboard event.
+	const session = await target.createCDPSession();
+	try { await session.send("Input.dispatchKeyEvent", { type: "rawKeyDown", key: key ?? (command === "copy" ? "c" : "v"), modifiers, commands: [command] }); }
+	finally { await session.detach(); }
+}
+async function syntheticDrop(target, paths, selector = '[data-testid="file-path-drop-zone"]') {
+	return target.$eval(selector, (zone, paths) => {
+		const transfer = new DataTransfer();
+		window.__syntheticPaths = new WeakMap();
+		window.lh = { platform: "darwin", getPathForFile(file) { return window.__syntheticPaths.get(file) ?? ""; } };
+		for (const [index, path] of paths.entries()) {
+			const file = new File(["never read"], `synthetic-display-${index}.pdf`, { type: "application/pdf" });
+			window.__syntheticPaths.set(file, path);
+			for (const method of ["text", "arrayBuffer", "stream"]) Object.defineProperty(file, method, { value() { throw new Error("File bytes must not be read"); } });
+			transfer.items.add(file);
+		}
+		const event = new DragEvent("drop", { bubbles: true, cancelable: true, dataTransfer: transfer });
+		zone.dispatchEvent(event); return event.defaultPrevented;
+	}, paths);
+}
+async function blur(target) { await target.evaluate(() => { document.activeElement?.blur(); }); }
+function seedChatFixtures() {
+	const usage = { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, totalTokens: 0, cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 } };
+	const transcript = Array.from({ length: 100 }, (_, index) => `Synthetic lesson paragraph ${index}: one and one make two. These are offline fixture notes.`).join("\n\n");
+	const assistant = (id, content) => ({ id, role: "assistant", api: "anthropic-messages", provider: "anthropic", model: "synthetic", timestamp: 1, stopReason: "toolUse", usage, content });
+	const call = (id, name, args) => ({ type: "toolCall", id, name, arguments: args });
+	const result = (id, toolCallId, toolName, details) => ({ id, role: "toolResult", toolCallId, toolName, content: [{ type: "text", text: "Synthetic tool completed." }], ...(details ? { details } : {}), isError: false, timestamp: 2 });
+	const quiz = { type: "check", nodeId: "addition", question: "What is 1 + 1?", options: [{ value: "two", label: "2" }, { value: "three", label: "3" }], explanation: "Adding one to one gives two.", correctAnswer: "two" };
+	const records = [
+		{ id: "path_teach", messages: [assistant("m_probe", [{ type: "text", text: transcript }, call("call_probe", "probe_done", { assessment: { strands: [{ strand: "Addition", assessment: "Ready for a check." }] } })]), result("m_probe_result", "call_probe", "probe_done", { ok: true }), assistant("m_quiz", [call("call_quiz", "quiz", quiz)])] },
+		{ id: "path_probe", messages: [assistant("m_probe_question", [{ type: "text", text: transcript }, call("call_probe_question", "probe", quiz)])] },
+		{ id: "path_practice", kind: "practice", messages: [assistant("m_problem", [{ type: "text", text: transcript }, call("call_problem", "problem", { statement: "Compute 1 + 1. Explain your reasoning.", mode: "recall", modelSolution: "1 + 1 = 2." })]), result("m_problem_result", "call_problem", "problem")] },
+	];
+	for (const record of records) {
+		record.messages.unshift({ id: "sent_user", role: "user", content: "Attached `/synthetic/transcript notes.pdf`", timestamp: 0 });
+		fs.writeFileSync(path.join(home, "data", "chats", `${record.id}.json`), JSON.stringify({ version: 1, title: `Synthetic ${record.id}`, createdAt: "2026-10-28T00:00:00.000Z", updatedAt: "2026-10-28T00:00:00.000Z", ...record }));
+	}
+}
+async function foldDock(target, barSelector) {
+	// Let growth/geometry muting settle, then use a real wheel gesture so
+	// stick-to-bottom records user intent instead of a programmatic clamp.
+	// The explicit reveal owns a bounded 2s fold-suppression window.
+	await target.evaluate(() => new Promise(resolve => setTimeout(resolve, 2250)));
+	const log = await target.$('[role="log"]'); const box = await log.boundingBox();
+	await target.mouse.move(box.x + box.width / 2, box.y + 100);
+	// Multiple real wheel frames let stick-to-bottom publish isAtBottom
+	// before DockOverlay evaluates the next away-from-bottom scroll event.
+	for (const deltaY of [-420, -420, -840]) {
+		await target.mouse.wheel({ deltaY });
+		await target.evaluate(() => new Promise(resolve => setTimeout(resolve, 100)));
+	}
+	try { await target.waitForSelector(barSelector, { visible: true, timeout: 5000 }); return true; }
+	catch {
+		coverageFailures.push({ url: target.url(), case: barSelector, message: "Native wheel did not expose collapsed bar", scrollers: await target.evaluate(() => [...document.querySelectorAll('[role="log"], [role="log"] *')].filter(element => element.scrollHeight > element.clientHeight + 100 && getComputedStyle(element).overflowY !== "visible").map(element => ({ tag: element.tagName, className: element.className, scrollTop: element.scrollTop, scrollHeight: element.scrollHeight, clientHeight: element.clientHeight }))) });
+		return false;
+	}
+}
+
+try {
+	fs.mkdirSync(path.join(home, "data", "chats"), { recursive: true });
+	fs.writeFileSync(path.join(home, "auth.json"), "{}\n");
+	seedChatFixtures();
+	const { getFontAxes } = require("next/dist/compiled/@next/font/dist/google/get-font-axes.js");
+	const { getGoogleFontsUrl } = require("next/dist/compiled/@next/font/dist/google/get-google-fonts-url.js");
+	const fonts = Object.fromEntries(["JetBrains Mono", "Source Sans 3"].map(family => [getGoogleFontsUrl(family, getFontAxes(family, ["variable"], ["normal"]), "swap"), `@font-face { font-family: '${family}'; src: local('Arial'); font-weight: 100 900; }`]));
+	fs.writeFileSync(path.join(home, "fonts.cjs"), `module.exports = ${JSON.stringify(fonts)};\n`);
+	const port = await freePort(); origin = `http://127.0.0.1:${port}`;
+	const env = { PATH: process.env.PATH, HOME: home, TMPDIR: home, NODE_ENV: "development", LH_DATA_DIR: path.join(home, "data"), LH_AUTH_FILE: path.join(home, "auth.json"), LH_IGNORE_ENV_KEYS: "1", NEXT_TELEMETRY_DISABLED: "1", NEXT_FONT_GOOGLE_MOCKED_RESPONSES: path.join(home, "fonts.cjs") };
+	const server = spawn(process.execPath, ["node_modules/next/dist/bin/next", "dev", "--hostname", "127.0.0.1", "--port", String(port)], { cwd: root, env, stdio: ["ignore", "pipe", "pipe"] }); children.push(server);
+	const captureServer = data => { serverLogs = (serverLogs + data).slice(-28000); };
+	server.stdout.on("data", captureServer); server.stderr.on("data", captureServer);
+	await startup(server, () => serverLogs, /Ready in/);
+	if (!process.argv.includes("--desktop-only")) {
+	const chrome = await puppeteer.launch({ executablePath: process.env.LH_TEST_CHROME || "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome", headless: true, userDataDir: path.join(home, "chrome-profile"), env, args: ["--disable-background-networking", "--disable-sync", "--no-first-run", "--disable-default-apps"] }); browsers.push(chrome);
+	page = await chrome.newPage(); await page.setViewport({ width: 1280, height: 900 }); await instrument(page);
+	await chrome.defaultBrowserContext().overridePermissions(origin, ["clipboard-read", "clipboard-write", "clipboard-sanitized-write"]);
+	const token = "`/synthetic/course notes.pdf`";
+	for (const route of ["/", "/chat/new"]) {
+		await open(page, route);
+		// Sidebar drops prevent browser navigation but must not stage paths or
+		// activate the right-content attachment indicator.
+		assert.equal(await page.$eval("aside", sidebar => {
+			const transfer = new DataTransfer(); transfer.items.add(new File(["not uploaded"], "sidebar.pdf"));
+			const event = new DragEvent("drop", { bubbles: true, cancelable: true, dataTransfer: transfer }); sidebar.dispatchEvent(event); return event.defaultPrevented;
+		}), true);
+		assert.equal(await page.$('[data-testid="file-path-drop-indicator"]'), null);
+		await expectValue(page, "");
+		// Browser mode has no bridge: prevent file navigation with a clear notice.
+		const prevented = await page.$eval('[data-testid="file-path-drop-zone"]', zone => {
+			const transfer = new DataTransfer(); transfer.items.add(new File(["not uploaded"], "notes.pdf"));
+			const event = new DragEvent("drop", { bubbles: true, cancelable: true, dataTransfer: transfer }); zone.dispatchEvent(event); return event.defaultPrevented;
+		});
+		assert.equal(prevented, true);
+		await page.waitForFunction(() => document.querySelector('[role="status"]')?.textContent.includes("desktop app"));
+		await fill(page, "read "); await page.keyboard.type(token + " now");
+		await expectValue(page, `read ${token} now`);
+		assert.equal(await page.$$eval('[data-file-path-input] [role="img"]', elements => elements.length), 1);
+		// Native browser arrows cross the atomic host without entering its label.
+		await caret(page, 5); await page.keyboard.press("ArrowRight");
+		assert.equal(await page.evaluate(() => !!document.getSelection().anchorNode?.parentElement?.closest('[role="img"]')), false);
+		await page.keyboard.press("Backspace"); await expectValue(page, "read  now");
+		await shortcut(page, "KeyZ"); await expectValue(page, `read ${token} now`);
+		await shortcut(page, "KeyZ", true); await expectValue(page, "read  now");
+		await shortcut(page, "KeyZ"); await caret(page, 5); await page.keyboard.press("Delete"); await expectValue(page, "read  now");
+		await shortcut(page, "KeyZ"); await expectValue(page, `read ${token} now`);
+		// Select the actual rendered label; copy must emit the full source token.
+		await page.$eval('[data-file-path-input] [role="img"] span', label => {
+			const range = document.createRange(); range.selectNodeContents(label); const selection = document.getSelection(); selection.removeAllRanges(); selection.addRange(range); document.dispatchEvent(new Event("selectionchange"));
+		});
+		await clipboardCommand(page, "copy");
+		assert.equal(await page.evaluate(() => navigator.clipboard.readText()), token);
+		await clipboardCommand(page, "cut", "Delete", 8);
+		await expectValue(page, "read  now");
+		assert.equal(await page.evaluate(() => navigator.clipboard.readText()), token, "Shift+Delete is native cut, not editor-only deletion");
+		await shortcut(page, "KeyZ"); await expectValue(page, `read ${token} now`);
+		// Clipboard image-only input must not erase the current selected path.
+		await page.$eval('[data-file-path-input]', editor => {
+			const host = editor.querySelector('[data-file-path-source]'); const range = document.createRange(); range.selectNode(host); const selection = document.getSelection(); selection.removeAllRanges(); selection.addRange(range); document.dispatchEvent(new Event("selectionchange"));
+			const data = new DataTransfer(); data.items.add(new File(["image fixture"], "image.png", { type: "image/png" }));
+			editor.dispatchEvent(new ClipboardEvent("paste", { bubbles: true, cancelable: true, clipboardData: data }));
+		});
+		await expectValue(page, `read ${token} now`);
+		// Pasting HTML-bearing clipboard content is plain text, at the range.
+		await page.evaluate(() => navigator.clipboard.writeText('<img src=x onerror="alert(1)">\n中'));
+		await clipboardCommand(page, "paste");
+		await expectValue(page, 'read <img src=x onerror="alert(1)">\n中 now');
+		assert.equal(await page.$('[data-file-path-input] img'), null);
+		await fill(page, "readthis"); await caret(page, 4);
+		assert.equal(await syntheticDrop(page, ["/synthetic/one.pdf", "~/two`final.pdf"]), true);
+		await expectValue(page, "read `/synthetic/one.pdf` ``~/two`final.pdf`` this");
+		assert.equal(posts.length, 0, "typing/paste/drop must never submit");
+		await fill(page, "one visible line"); await caret(page, "one visible line".length);
+		const beforeNewline = await page.$eval(inputSelector, element => element.getBoundingClientRect().height);
+		await page.keyboard.down("Shift"); await page.keyboard.press("Enter"); await page.keyboard.up("Shift");
+		await expectValue(page, "one visible line\n");
+		const afterNewline = await page.$eval(inputSelector, element => {
+			const range = document.getSelection().getRangeAt(0); const rect = range.getBoundingClientRect();
+			return { height: element.getBoundingClientRect().height, caret: { top: rect.top, height: rect.height }, html: element.innerHTML };
+		});
+		// Record this independently so a visual editor regression does not hide
+		// the higher-priority actual Electron/target-routing evidence below.
+		try { assert.ok(afterNewline.height > beforeNewline, `Trailing newline must occupy a visible blank line: ${JSON.stringify({ beforeNewline, afterNewline })}`); }
+		catch (error) { visualFailures.push({ route, message: error.message }); }
+		await page.keyboard.type("second line");
+		const afterTyping = await read(page);
+		try { assert.equal(afterTyping, "one visible line\nsecond line", "Typing after Shift+Enter must stay after the newline"); }
+		catch (error) { visualFailures.push({ route, message: error.message }); }
+		assert.equal(posts.length, 0, "Shift+Enter is a newline, never submit");
+		await fill(page, "composer fallback"); await blur(page);
+		await syntheticDrop(page, ["/synthetic/default.pdf"]);
+		await expectValue(page, "composer fallback `/synthetic/default.pdf`");
+		// Small viewport: wrapped multiline content stays scrollable inside its editor.
+		await page.setViewport({ width: 900, height: 520 });
+		await fill(page, (`${token} a long synthetic line wrapping at narrow widths.\n`).repeat(24));
+		const sizing = await page.$eval(inputSelector, element => ({ height: element.clientHeight, scrollHeight: element.scrollHeight, overflowY: getComputedStyle(element).overflowY, bodyWidth: document.body.scrollWidth, viewport: innerWidth }));
+		assert.ok(sizing.scrollHeight > sizing.height && sizing.height > 0, JSON.stringify(sizing));
+		assert.ok(["auto", "scroll"].includes(sizing.overflowY));
+		assert.ok(sizing.bodyWidth <= sizing.viewport + 1, JSON.stringify(sizing));
+		const screenshot = path.join(home, `chrome-${route === "/" ? "home" : "new"}.png`); await page.screenshot({ path: screenshot }); screenshots.push({ surface: route, bytes: fs.statSync(screenshot).size, sizing });
+		await page.setViewport({ width: 1280, height: 900 });
+		checks.push(`${route}: native typing/chips/arrows/deletion/undo-redo/full-source clipboard/plaintext paste/caret drop/newlines/wrap-scroll`);
+	}
+	// Only an explicit Enter may initiate a send; agent endpoint is refused.
+	await fill(page, "explicit synthetic send `/synthetic/one.pdf`");
+	await page.keyboard.press("Enter");
+	await page.waitForFunction(() => /^\/chat\/chat_/.test(location.pathname));
+	await new Promise((resolve, reject) => {
+		const deadline = Date.now() + 15000;
+		const inspect = () => { if (posts.length) resolve(); else if (Date.now() > deadline) reject(new Error("Explicit Enter did not send")); else setTimeout(inspect, 50); }; inspect();
+	});
+	assert.equal(posts.length, 1); assert.equal(posts[0].body.input.text, "explicit synthetic send `/synthetic/one.pdf`");
+	checks.push("Explicit Enter submitted exactly one full-source prompt; endpoint intercepted/refused");
+
+	// These raw JSON fixtures are synthetic native records, never store imports.
+	const reading = '[data-testid="reading-thinking-field"] [data-file-path-input]';
+	const question = '[data-testid="thinking-field"] [data-file-path-input]';
+	const practice = '[data-testid="practice-thinking-field"] [data-file-path-input]';
+	await open(page, "/chat/path_teach");
+	await page.waitForSelector('[data-testid="teach-check-reveal"]', { visible: true });
+	assert.equal(await page.$eval('[data-testid="user-message"] [role="img"]', chip => chip.title), "/synthetic/transcript notes.pdf");
+	assert.equal(await page.$eval('[data-testid="user-message"] [role="img"]', chip => chip.textContent), "transcript notes.pdf");
+	checks.push("Seeded sent learner message renders a filename chip with full-path title; raw record retains quoted full path");
+	await blur(page); await syntheticDrop(page, ["/synthetic/reading.pdf"]);
+	await expectValue(page, "`/synthetic/reading.pdf`", reading);
+	assert.equal(await read(page, question), "");
+	checks.push("Unrevealed teaching check: unfocused drop lands in reading-thinking via dictation registry");
+	await page.locator('[data-testid="teach-check-reveal"]').click();
+	await page.waitForSelector(question, { visible: true });
+	await fill(page, "AB", reading); await caret(page, 1, reading);
+	await syntheticDrop(page, ["/synthetic/focused-reading.pdf"]);
+	await expectValue(page, "A `/synthetic/focused-reading.pdf` B", reading);
+	assert.equal(await read(page, question), "", "focused reading field overrides opened question default");
+	await blur(page); await syntheticDrop(page, ["/synthetic/question.pdf"]);
+	await expectValue(page, "`/synthetic/question.pdf`", question);
+	checks.push("Opened teaching check: current reading focus wins; otherwise default routes to question-thinking");
+	if (await foldDock(page, '[data-testid="question-dock-bar"]')) {
+		await blur(page); await syntheticDrop(page, ["/synthetic/collapsed-question.pdf"]);
+		await expectValue(page, "`/synthetic/question.pdf` `/synthetic/collapsed-question.pdf`", question);
+		await page.locator('[data-testid="question-dock-bar"]').click();
+		await page.waitForSelector(question, { visible: true });
+		assert.equal(await read(page, question), "`/synthetic/question.pdf` `/synthetic/collapsed-question.pdf`");
+		checks.push("Collapsed revealed teaching dock keeps question-thinking claim/state through expansion");
+	}
+	await open(page, "/chat/path_probe"); await page.waitForSelector(question, { visible: true });
+	await blur(page); await syntheticDrop(page, ["/synthetic/probe.pdf"]);
+	await expectValue(page, "`/synthetic/probe.pdf`", question);
+	checks.push("Probe-phase pending question default routes to question-thinking");
+	await open(page, "/chat/path_practice"); await page.waitForSelector(practice, { visible: true });
+	await blur(page); await syntheticDrop(page, ["/synthetic/practice.pdf"]);
+	await expectValue(page, "`/synthetic/practice.pdf`", practice);
+	checks.push("Expanded practice thinking is the unfocused drop default");
+	if (await foldDock(page, '[data-testid="practice-dock-bar"]')) {
+		await blur(page); await syntheticDrop(page, ["/synthetic/collapsed-practice.pdf"]);
+		// Practice keeps the owning hook/state mounted, but hides its field
+		// by returning the bar. Inspect the controlled text after expansion.
+		await page.waitForFunction(() => document.querySelector('[role="status"]')?.textContent.includes("File paths attached"));
+		await page.locator('[data-testid="practice-dock-bar"]').click();
+		await page.waitForSelector(practice, { visible: true });
+		await expectValue(page, "`/synthetic/practice.pdf` `/synthetic/collapsed-practice.pdf`", practice);
+		checks.push("Collapsed practice thinking keeps its claim/state through expansion without submission");
+	}
+	assert.equal(posts.length, 1, "all claim/drop cases stage text only");
+
+	}
+	// Actual Electron main + actual sandboxed preload. Temporary launcher sets
+	// userData BEFORE production main appends its -dev suffix or takes a lock.
+	const debugPort = await freePort();
+	const launcher = path.join(home, "electron-launcher.cjs");
+	fs.mkdirSync(path.join(home, "desktop-profile"), { recursive: true });
+	fs.mkdirSync(path.join(home, "desktop-profile-dev"), { recursive: true });
+	fs.writeFileSync(launcher, `const {app,session}=require('electron');\napp.setPath('home',${JSON.stringify(home)});\napp.setPath('userData',${JSON.stringify(path.join(home, "desktop-profile"))});\napp.commandLine.appendSwitch('remote-debugging-port',${JSON.stringify(String(debugPort))});\napp.commandLine.appendSwitch('disable-background-networking');\napp.commandLine.appendSwitch('disable-sync');\napp.whenReady().then(()=>session.defaultSession.webRequest.onBeforeRequest((details,cb)=>{let u;try{u=new URL(details.url)}catch{return cb({cancel:true})}cb({cancel:!(${JSON.stringify(origin)}===u.origin||(u.protocol==='ws:'&&u.host===${JSON.stringify(new URL(origin).host)})||['about:','data:','devtools:'].includes(u.protocol))});}));\nrequire(${JSON.stringify(path.join(root, "electron", "main.cjs"))});\nconsole.log('LH_FILE_PATH_PROFILE '+JSON.stringify({home:app.getPath('home'),userData:app.getPath('userData')}));\n`);
+	const electron = spawn(require("electron"), [launcher], { cwd: root, env: { ...env, LH_DEV_URL: origin }, stdio: ["ignore", "pipe", "pipe"] }); children.push(electron);
+	const captureElectron = data => { electronLogs = (electronLogs + data).slice(-24000); }; electron.stdout.on("data", captureElectron); electron.stderr.on("data", captureElectron);
+	await startup(electron, () => electronLogs, /DevTools listening on (ws:\/\/[^\s]+)/, 45000);
+	const profile = JSON.parse(electronLogs.match(/LH_FILE_PATH_PROFILE ([^\r\n]+)/)[1]);
+	assert.equal(profile.home, home); assert.equal(profile.userData, path.join(home, "desktop-profile-dev"));
+	const desktopLaunch = { executable: require("electron"), args: [launcher], LH_DEV_URL: origin, HOME: home, userDataBeforeMain: path.join(home, "desktop-profile"), actualProfile: profile, cleanup: "all temporary profiles/data/fixtures removed on exit" };
+	const endpoint = electronLogs.match(/DevTools listening on (ws:\/\/[^\s]+)/)[1];
+	const desktop = await puppeteer.connect({ browserWSEndpoint: endpoint }); browsers.push(desktop);
+	const desktopPage = await desktop.waitForTarget(target => target.type() === "page").then(target => target.page());
+	await instrument(desktopPage); page = desktopPage;
+	await open(desktopPage, "/chat/new");
+	assert.equal(await desktopPage.evaluate(() => typeof window.lh?.getPathForFile), "function");
+	const fixturePath = path.join(home, "actual OS-backed α `notes`.pdf"); fs.writeFileSync(fixturePath, "%PDF-1.7\nsynthetic offline fixture\n");
+	await desktopPage.evaluate(() => { const input = document.createElement("input"); input.type = "file"; input.id = "os-backed-fixture"; document.body.append(input); });
+	await (await desktopPage.$("#os-backed-fixture")).uploadFile(fixturePath);
+	const resolved = await desktopPage.evaluate(() => {
+		const input = document.querySelector("#os-backed-fixture");
+		return { count: input.files.length, actual: window.lh.getPathForFile(input.files[0]), virtual: window.lh.getPathForFile(new File(["virtual"], "/not/a/backing/path.pdf")) };
+	});
+	assert.equal(resolved.count, 1); assert.equal(resolved.actual, fixturePath); assert.equal(resolved.virtual, "");
+	await fill(desktopPage, "readthis"); await caret(desktopPage, 4);
+	const beforeDesktopDrop = posts.length;
+	assert.equal(await desktopPage.evaluate(() => {
+		const file = document.querySelector("#os-backed-fixture").files[0];
+		for (const method of ["text", "arrayBuffer", "stream"]) Object.defineProperty(file, method, { value() { throw new Error("No file content read"); } });
+		const transfer = new DataTransfer(); transfer.items.add(file);
+		const event = new DragEvent("drop", { bubbles: true, cancelable: true, dataTransfer: transfer });
+		document.querySelector('[data-testid="file-path-drop-zone"]').dispatchEvent(event); return event.defaultPrevented;
+	}), true);
+	const expectedQuoted = "``" + fixturePath + "``";
+	await expectValue(desktopPage, `read ${expectedQuoted} this`);
+	assert.equal(await desktopPage.$eval('[data-file-path-input] [role="img"]', chip => chip.title), fixturePath);
+	assert.equal(posts.length, beforeDesktopDrop, "actual OS-backed desktop drop must stage only");
+	assert.ok(fs.existsSync(fixturePath));
+	assert.deepEqual(fs.readdirSync(path.join(home, "data")).filter(name => /upload|attachment/i.test(name)), []);
+	checks.push("Actual Electron production preload: Puppeteer-selected OS-backed File resolves exact Unicode/backtick full path; virtual File returns empty; real DataTransfer drop inserts at caret without submit or file reads");
+	assert.deepEqual(errors, []);
+	console.log(JSON.stringify({ checks, visualFailures, coverageFailures, screenshots, desktopLaunch, postsIntercepted: posts.length, blockedExternalRequests: blocked, isolation: "temporary HOME/data/auth/browser+Electron profiles; synthetic catalog; agent POSTs refused; no providers", origin }, null, 2));
+	assert.deepEqual(visualFailures, [], "Visible trailing-newline/caret projection must pass");
+	assert.deepEqual(coverageFailures, [], "Required collapsed target coverage must run");
+} catch (error) {
+	console.error(error);
+	console.error(JSON.stringify({ checks, visualFailures, coverageFailures, errors, consoleErrors, networkFailures: networkFailures.slice(-30), posts, origin, url: page?.url(), dom: await page?.evaluate(() => ({ inputs: [...document.querySelectorAll('[data-file-path-input]')].map(element => ({ placeholder: element.getAttribute("data-placeholder"), text: element.textContent, html: element.innerHTML.slice(0, 1200) })), text: document.body.innerText.slice(-2600) })).catch(() => null), serverLogs, electronLogs }, null, 2));
+	process.exitCode = 1;
+} finally {
+	shuttingDown = true;
+	for (const browser of browsers.reverse()) { try { await browser.close(); } catch {} }
+	for (const child of children.reverse()) await stop(child);
+	fs.rmSync(home, { recursive: true, force: true });
+}

scripts/smoke-opening-prompt.mjs

@@ -109,14 +109,14 @@ try {
 		// Release synthetic streams from prior cases rather than pin slots.
 		await Promise.all(held.splice(0).map(request => request.abort("aborted").catch(() => {})));
 		await page.goto(origin + route, { waitUntil: "domcontentloaded", timeout: 120000 });
-		await page.waitForSelector(route === "/" ? "textarea" : '[data-testid="composer"] textarea');
+		await page.waitForSelector(route === "/" ? "[data-file-path-input]" : '[data-testid="composer"] [data-file-path-input]');
 		await page.waitForFunction(() => !document.querySelector('[data-testid="setup-cta"]') && !document.querySelector('[data-testid="setup-cta-keys"]'));
 	}
 	async function fill(text) {
 		await page.evaluate(value => {
-			const textarea = document.querySelector('[data-testid="composer"] textarea') || document.querySelector("textarea");
-			Object.getOwnPropertyDescriptor(HTMLTextAreaElement.prototype, "value").set.call(textarea, value);
-			textarea.dispatchEvent(new Event("input", { bubbles: true }));
+			const input = document.querySelector('[data-testid="composer"] [data-file-path-input]') || document.querySelector("[data-file-path-input]");
+			input.textContent = value;
+			input.dispatchEvent(new Event("input", { bubbles: true }));
 		}, text);
 	}
 	async function submit() {
@@ -127,7 +127,10 @@ try {
 		await page.locator('button[aria-label="Start session"], [data-testid="composer"] button[aria-label="Send"]').click();
 	}
 	async function stash(id) { return page.evaluate(chat => sessionStorage.getItem(`lh.openingPrompt.${chat}`), id); }
-	async function assertDraft(text) { await page.waitForFunction(value => document.querySelector('[data-testid="composer"] textarea')?.value === value, {}, text); }
+	async function assertDraft(text) { await page.waitForFunction(value => {
+		const input = document.querySelector('[data-testid="composer"] [data-file-path-input]');
+		return input && [...input.childNodes].map(node => node.nodeType === 1 ? node.getAttribute("data-file-path-source") ?? node.textContent : node.textContent).join("") === value;
+	}, {}, text); }
 	const long = "A full synthetic syllabus — 世界 & ? #. ".repeat(1200).trim();
 	for (const route of ["/", "/chat/new"]) {
 		for (const text of ["a short synthetic topic", long]) {
@@ -163,7 +166,7 @@ try {
 		await fill(long); await submit();
 		await page.waitForSelector('[role="alert"]');
 		assert.equal(new URL(page.url()).pathname, route);
-		assert.equal(await page.$eval("textarea", element => element.value), long);
+		assert.equal(await page.$eval("[data-file-path-input]", element => [...element.childNodes].map(node => node.nodeType === 1 ? node.getAttribute("data-file-path-source") ?? node.textContent : node.textContent).join("")), long);
 		assert.equal(posts.length, sendCount);
 		assert.equal(creates.length, createCount + 1);
 		await page.evaluate(() => { window.failOpeningStorage = false; });
@@ -239,7 +242,7 @@ try {
 	console.log(JSON.stringify({ checks, pageErrors: errors, isolation: "synthetic catalog/POST+streams; empty auth; no providers", origin }, null, 2));
 } catch (err) {
 	console.error(err);
-	console.error(JSON.stringify({ checks, errors, url: page?.url(), dom: await page?.evaluate(() => ({ textareas: [...document.querySelectorAll('textarea')].map(e => ({ length: e.value.length, placeholder: e.placeholder })), buttons: [...document.querySelectorAll('button[aria-label="Send"], button[aria-label="Start session"]')].map(e => ({ disabled: e.disabled, label: e.getAttribute('aria-label') })), alerts: [...document.querySelectorAll('[role="alert"]')].map(e => e.textContent), failStorage: window.failOpeningStorage, text: document.body.innerText.slice(-1200) })).catch(() => null) }, null, 2));
+	console.error(JSON.stringify({ checks, errors, url: page?.url(), dom: await page?.evaluate(() => ({ inputs: [...document.querySelectorAll('[data-file-path-input]')].map(e => ({ length: [...e.childNodes].map(n => n.nodeType === 1 ? n.getAttribute('data-file-path-source') ?? n.textContent : n.textContent).join('').length, placeholder: e.getAttribute('data-placeholder') })), buttons: [...document.querySelectorAll('button[aria-label="Send"], button[aria-label="Start session"]')].map(e => ({ disabled: e.disabled, label: e.getAttribute('aria-label') })), alerts: [...document.querySelectorAll('[role="alert"]')].map(e => e.textContent), failStorage: window.failOpeningStorage, text: document.body.innerText.slice(-1200) })).catch(() => null) }, null, 2));
 	console.error(logs); process.exitCode = 1;
 } finally {
 	await browser?.close();

src/core/file-paths.ts

@@ -0,0 +1,86 @@
+/** A lossless projection of plain learner text, not a Markdown parser. */
+export type FilePathPart =
+	| { kind: "text"; text: string; start: number; end: number }
+	| { kind: "path"; text: string; path: string; start: number; end: number };
+
+// No filesystem access or normalization: even punctuation and backslashes can
+// be legitimate POSIX filename characters. Only rooted syntax is required.
+function isFilePath(path: string): boolean {
+	if (/[\u0000-\u001f\u007f-\u009f\u2028\u2029]/u.test(path)) return false;
+	return path.startsWith("/")
+		|| path.startsWith("~/")
+		|| /^[a-z]:[\\/]/i.test(path)
+		|| /^\\\\[^\\/]+[\\/][^\\/]+(?:[\\/]|$)/u.test(path);
+}
+
+/**
+ * Wrap a rooted path for storage/transmission as ordinary, lossless text.
+ * CommonMark's one-space padding prevents edge backticks joining delimiters.
+ */
+export function quoteFilePath(path: string): string {
+	if (!isFilePath(path)) throw new TypeError("Expected a single-line rooted file path");
+	let width = 1;
+	for (const run of path.matchAll(/`+/g)) width = Math.max(width, run[0].length + 1);
+	const delimiter = "`".repeat(width);
+	const padding = path.startsWith("`") || path.endsWith("`") ? " " : "";
+	return `${delimiter}${padding}${path}${padding}${delimiter}`;
+}
+
+/**
+ * Recognize every complete backtick-wrapped rooted path, even beside words.
+ * Delimiters are whole runs of exactly equal length; a run inside another
+ * code span is never reconsidered as a partial path token. Offsets are JS
+ * string (UTF-16) offsets and `text` always slices the exact original input.
+ */
+export function parseFilePaths(text: string): FilePathPart[] {
+	const runs = Array.from(text.matchAll(/`+/g), (match) => ({
+		start: match.index,
+		end: match.index + match[0].length,
+		width: match[0].length,
+	}));
+	// The next same-width run lets unmatched openers remain plain text without
+	// repeatedly scanning the rest of a long draft.
+	const next = new Map<number, number>();
+	const closing = new Map<number, number>();
+	for (let i = runs.length - 1; i >= 0; i--) {
+		const width = runs[i]!.width;
+		const match = next.get(width);
+		if (match !== undefined) closing.set(i, match);
+		next.set(width, i);
+	}
+
+	const parts: FilePathPart[] = [];
+	let plainStart = 0;
+	for (let i = 0; i < runs.length; i++) {
+		const closeIndex = closing.get(i);
+		if (closeIndex === undefined) continue;
+		const open = runs[i]!;
+		const close = runs[closeIndex]!;
+		let path = text.slice(open.end, close.start);
+		// CommonMark strips exactly one space at each edge, not all whitespace.
+		if (path.startsWith(" ") && path.endsWith(" ") && /[^ ]/.test(path)) {
+			path = path.slice(1, -1);
+		}
+		if (isFilePath(path)) {
+			if (plainStart < open.start) {
+				parts.push({ kind: "text", text: text.slice(plainStart, open.start), start: plainStart, end: open.start });
+			}
+			parts.push({ kind: "path", text: text.slice(open.start, close.end), path, start: open.start, end: close.end });
+			plainStart = close.end;
+		}
+		i = closeIndex;
+	}
+	if (plainStart < text.length) {
+		parts.push({ kind: "text", text: text.slice(plainStart), start: plainStart, end: text.length });
+	}
+	return parts;
+}
+
+/** Basename for display only; the original full path remains untouched. */
+export function filePathLabel(path: string): string {
+	const windows = /^[a-z]:[\\/]/i.test(path) || path.startsWith("\\\\");
+	const separator = windows ? /[\\/]/ : /\//;
+	const trimmed = windows ? path.replace(/[\\/]+$/, "") : path.replace(/\/+$/, "");
+	if (!trimmed || (windows && /^[a-z]:$/i.test(trimmed)) || trimmed === "~") return path;
+	return trimmed.split(separator).at(-1) || path;
+}

src/core/index.ts

@@ -42,6 +42,8 @@ export * from "./math-delims.ts";
 export * from "./native-messages.ts";
 export * from "./compaction.ts";
 export * from "./input-events.ts";
+export { parseFilePaths, quoteFilePath, filePathLabel } from "./file-paths.ts";
+export type { FilePathPart } from "./file-paths.ts";
 // Wave D (owner-approved 2026-09-26): the client view model — the grouping
 // canon (one continuous assistant document, step separators) ported from
 // the deleted server projection to the client side. Pure, browser-safe.

tests/desktop-platform.test.ts

@@ -96,7 +96,7 @@ describe("desktop window chrome", () => {
 		runInNewContext(readFileSync(new URL("../electron/preload.cjs", import.meta.url), "utf8"), context);
 		assert.equal(bridge.platform, "win32");
 		assert.deepEqual(Object.keys(bridge).sort(), [
-			"chatgpt", "checkForUpdates", "expandWindow", "getUpdateState", "getZoom", "installUpdate", "onOpenSettings", "onUpdateStatus", "onZoom", "platform", "subscriptions",
+			"chatgpt", "checkForUpdates", "expandWindow", "getPathForFile", "getUpdateState", "getZoom", "installUpdate", "onOpenSettings", "onUpdateStatus", "onZoom", "platform", "subscriptions",
 		]);
 		assert.deepEqual(Object.keys(bridge.subscriptions as object).sort(), ["cancel", "consent", "disconnect", "login", "onChange", "open", "respond", "retry", "status"]);
 	});

tests/file-path-chip.test.tsx

@@ -0,0 +1,89 @@
+import React from "react";
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import { renderToStaticMarkup } from "react-dom/server";
+import { parseHTML } from "linkedom";
+import { FilePathChip, PathText } from "../components/file-path-chip.tsx";
+import { quoteFilePath } from "../src/core/file-paths.ts";
+
+function documentFor(node: React.ReactNode) {
+	return parseHTML(`<html><body>${renderToStaticMarkup(node)}</body></html>`).document;
+}
+
+describe("FilePathChip", () => {
+	it("shows a filename and decorative type icon with an accessible full path", () => {
+		const path = "/tmp/course notes/α.pdf";
+		const document = documentFor(<FilePathChip path={path} />);
+		const chip = document.body.firstElementChild!;
+		assert.equal(chip.tagName, "SPAN");
+		assert.equal(chip.textContent, "α.pdf");
+		assert.equal(chip.getAttribute("title"), path);
+		assert.equal(chip.getAttribute("role"), "img");
+		assert.equal(chip.getAttribute("aria-label"), path);
+		assert.equal(chip.querySelector("svg")!.getAttribute("aria-hidden"), "true");
+		assert.ok(chip.querySelector(".lucide-file-text"));
+		assert.equal(document.querySelector("a, button, input, [tabindex]"), null);
+		assert.equal(chip.getAttributeNames().some((name) => name.toLowerCase() === "contenteditable"), false);
+		assert.ok(chip.classList.contains("inline-flex"));
+		assert.ok(chip.querySelector(".truncate"));
+	});
+
+	it("supports atomic editor rendering without requiring an editor in transcripts", () => {
+		const document = documentFor(<FilePathChip path="C:\\notes\\chapter.txt" contentEditable={false} className="editor-chip" />);
+		const chip = document.body.firstElementChild!;
+		// React SSR emits contentEditable; linkedom preserves attribute case.
+		const editableAttribute = chip.getAttributeNames().find((name) => name.toLowerCase() === "contenteditable")!;
+		assert.equal(chip.getAttribute(editableAttribute), "false");
+		assert.ok(chip.classList.contains("editor-chip"));
+		assert.equal(chip.textContent, "chapter.txt");
+	});
+
+	it("chooses type icons without accessing files or changing their names", () => {
+		for (const [filename, icon] of [
+			["figure.PNG", "file-image"], ["lecture.mp3", "file-headphone"], ["clip.mp4", "file-play"],
+			["course.zip", "file-archive"], ["data.csv", "file-spreadsheet"], ["example.ts", "file-code"],
+			["notes.md", "file-text"], ["unknown.xyz", "file"],
+		]) {
+			const document = documentFor(<FilePathChip path={`/not/real/${filename}`} />);
+			assert.equal(document.body.textContent, filename);
+			assert.ok(document.querySelector(`.lucide-${icon}`));
+		}
+	});
+
+	it("keeps dangerous filename HTML inert in both label and title", () => {
+		const path = '/tmp/<img src=x onerror="alert(1)">.pdf';
+		const document = documentFor(<FilePathChip path={path} />);
+		assert.equal(document.body.textContent, '<img src=x onerror="alert(1)">.pdf');
+		assert.equal(document.body.firstElementChild!.getAttribute("title"), path);
+		assert.equal(document.querySelector("img, script, [onerror], a"), null);
+	});
+});
+
+describe("PathText", () => {
+	it("keeps ordinary text, markup-looking text and inline code completely unchanged", () => {
+		const text = 'Ordinary <b>prose</b>\n`code` ./relative `file:///tmp/a` & words';
+		const document = documentFor(<PathText text={text} />);
+		assert.equal(document.body.textContent, text);
+		assert.equal(document.body.children.length, 0);
+		assert.equal(renderToStaticMarkup(<PathText text="" />), "");
+	});
+
+	it("renders all quoted platforms, adjacent words and paths containing backticks", () => {
+		const paths = ["/tmp/a.pdf", "C:\\notes\\b.md", "\\\\server\\share\\c.png", "~/d`e.txt"];
+		const text = `before${paths.map(quoteFilePath).join(" then ")}after`;
+		const document = documentFor(<PathText text={text} />);
+		const chips = document.querySelectorAll('[role="img"]');
+		assert.equal(chips.length, paths.length);
+		assert.deepEqual(Array.from(chips, (chip) => chip.getAttribute("title")), paths);
+		assert.equal(document.body.textContent, "beforea.pdf then b.md then c.png then d`e.txtafter");
+		assert.equal(text, `before${paths.map(quoteFilePath).join(" then ")}after`, "presentation never rewrites saved text");
+	});
+
+	it("does not interpret HTML in ordinary text or path labels", () => {
+		const path = '/tmp/<img src=x onerror="alert(1)">.png';
+		const document = documentFor(<PathText text={`<script>alert(1)</script> ${quoteFilePath(path)}`} />);
+		assert.equal(document.querySelector("script, img, [onerror], a"), null);
+		assert.equal(document.querySelector('[role="img"]')!.getAttribute("title"), path);
+		assert.equal(document.body.textContent, '<script>alert(1)</script> <img src=x onerror="alert(1)">.png');
+	});
+});

tests/file-path-drop-zone.test.tsx

@@ -0,0 +1,223 @@
+import React, { act } from "react";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { afterEach, test } from "node:test";
+import { parseHTML } from "linkedom";
+import { FilePathDropZone } from "../components/file-path-drop-zone.tsx";
+import { useDictationTarget } from "../components/dictation.tsx";
+import { PathInput } from "../components/path-input.tsx";
+import { readPathInput, restorePathSelection } from "../components/path-input-dom.ts";
+import { quoteFilePath } from "../src/core/file-paths.ts";
+
+let cleanup: (() => Promise<void>) | undefined;
+afterEach(async () => { await cleanup?.(); cleanup = undefined; });
+
+/** No native DataTransfer/Selection in linkedom. These shims exercise React's
+ * real bubbling handlers and the editor's logical caret contract, not OS drag. */
+async function fixture({ desktop = true, claimed = true } = {}) {
+	const { window: win, document: doc } = parseHTML("<html><body><div id='root'></div></body></html>");
+	let active: Element = doc.body;
+	Object.defineProperty(doc, "activeElement", { get: () => active });
+	const selection = {
+		anchorNode: null as Node | null, anchorOffset: 0, focusNode: null as Node | null, focusOffset: 0,
+		setBaseAndExtent(anchorNode: Node, anchorOffset: number, focusNode: Node, focusOffset: number) {
+			Object.assign(this, { anchorNode, anchorOffset, focusNode, focusOffset });
+		},
+	};
+	Object.assign(doc, { getSelection: () => selection, oninput: null });
+	win.HTMLElement.prototype.focus = function () { active = this; };
+	const resolved: File[] = [];
+	const backingPaths = new Map<File, string | Error>();
+	const appends: string[] = [];
+	let byteReads = 0;
+	let uploads = 0;
+	let submits = 0;
+	let keys = 0;
+	let value = "readthis";
+	const bridge = desktop ? { getPathForFile(file: File) {
+		resolved.push(file);
+		const result = backingPaths.get(file);
+		if (result instanceof Error) throw result;
+		return result ?? "";
+	} } : undefined;
+	const previous = new Map<string, PropertyDescriptor | undefined>();
+	for (const [name, next] of Object.entries({
+		React, window: win, document: doc, Node: win.Node, HTMLElement: win.HTMLElement, Element: win.Element,
+		Event: win.Event, CustomEvent: win.CustomEvent, IS_REACT_ACT_ENVIRONMENT: true,
+		fetch: () => { uploads++; throw new Error("No network expected for file drops"); },
+	})) {
+		previous.set(name, Object.getOwnPropertyDescriptor(globalThis, name));
+		Object.defineProperty(globalThis, name, { configurable: true, writable: true, value: next });
+	}
+	const oldBridge = Object.getOwnPropertyDescriptor(win, "lh");
+	Object.defineProperty(win, "lh", { configurable: true, value: bridge });
+	const { createRoot } = await import("react-dom/client");
+	const root = createRoot(doc.getElementById("root")!);
+	function Harness() {
+		useDictationTarget((text) => appends.push(text), claimed);
+		return <>
+			<aside data-testid="sidebar">Sidebar</aside>
+			<FilePathDropZone>
+				<form onSubmit={(event) => { event.preventDefault(); submits++; }}>
+					<PathInput data-testid="editor" value={value} onValueChange={(next) => { value = next; draw(); }} onKeyDown={() => { keys++; }} />
+					<button type="button" data-testid="elsewhere">Elsewhere</button>
+					<div data-testid="content">Content away from the input</div>
+				</form>
+			</FilePathDropZone>
+		</>;
+	}
+	function draw() { root.render(<Harness />); }
+	await act(async () => { draw(); });
+	cleanup = async () => {
+		await act(async () => { root.unmount(); });
+		if (oldBridge) Object.defineProperty(win, "lh", oldBridge);
+		else delete (win as unknown as Record<string, unknown>).lh;
+		for (const [name, descriptor] of previous) {
+			if (descriptor) Object.defineProperty(globalThis, name, descriptor);
+			else delete (globalThis as Record<string, unknown>)[name];
+		}
+	};
+	const editor = doc.querySelector<HTMLElement>('[data-testid="editor"]')!;
+	function file(name: string, path?: string | Error) {
+		const result = new File(["synthetic bytes must never be read"], name, { type: "application/pdf" });
+		for (const method of ["text", "arrayBuffer", "stream"] as const) {
+			Object.defineProperty(result, method, { value: () => { byteReads++; throw new Error("No file content reads"); } });
+		}
+		if (path !== undefined) backingPaths.set(result, path);
+		return result;
+	}
+	function transfer(files: File[], directories: number[] = [], types = ["Files"]) {
+		return {
+			types,
+			files: Object.assign([...files], { item: (index: number) => files[index] ?? null }),
+			items: files.map((file, index) => ({ kind: "file", type: file.type, getAsFile: () => file, webkitGetAsEntry: () => ({ isDirectory: directories.includes(index), isFile: !directories.includes(index) }) })),
+			dropEffect: "none",
+		};
+	}
+	async function event(type: string, dataTransfer = transfer([]), target: Element = doc.querySelector('[data-testid="content"]')!) {
+		const event = Object.assign(new win.Event(type, { bubbles: true, cancelable: true }), { dataTransfer });
+		await act(async () => { target.dispatchEvent(event); });
+		return event;
+	}
+	return {
+		doc, editor, appends, resolved, file, transfer, event,
+		get value() { return value; },
+		get status() { return doc.querySelector('[role="status"]')?.textContent ?? ""; },
+		focusEditor(offset: number) {
+			editor.focus();
+			restorePathSelection(editor, { anchor: offset, focus: offset });
+			doc.dispatchEvent(new win.Event("selectionchange"));
+		},
+		assertPathOnly() { assert.equal(byteReads, 0); assert.equal(uploads, 0); assert.equal(submits, 0); assert.equal(keys, 0); },
+	};
+}
+
+test("desktop drop inserts quoted paths at the focused editor caret instead of the dictation claimant", async () => {
+	const f = await fixture();
+	f.focusEditor(4);
+	const paths = ["/actual/course notes.pdf", "C:\\course\\chapter`one.pdf", "\\\\host\\share\\図.png"];
+	const files = paths.map((path, index) => f.file(`display-name-${index}.pdf`, path));
+	const dropped = await f.event("drop", f.transfer(files));
+	assert.equal(dropped.defaultPrevented, true);
+	assert.equal(f.value, `read ${paths.map(quoteFilePath).join(" ")} this`);
+	assert.equal(readPathInput(f.editor), f.value);
+	assert.equal(f.doc.activeElement, f.editor);
+	assert.deepEqual(f.appends, [], "focused editor wins over the registered question field");
+	assert.deepEqual(f.resolved, files, "only Electron's full path, never File.name, enters the draft");
+	assert.match(f.status, /File paths attached/);
+	f.assertPathOnly();
+});
+
+test("unfocused drop uses the dictation target registry, not the last focused editor", async () => {
+	const f = await fixture();
+	f.focusEditor(4);
+	f.doc.querySelector<HTMLElement>('[data-testid="elsewhere"]')!.focus();
+	const paths = ["~/notes one.pdf", "/tmp/notes`final`"];
+	await f.event("drop", f.transfer(paths.map((path) => f.file("not-a-physical-path.pdf", path))));
+	assert.deepEqual(f.appends, [paths.map(quoteFilePath).join(" ")]);
+	assert.equal(f.value, "readthis", "saved editor caret must not override current default target");
+	f.assertPathOnly();
+});
+
+test("browser drop prevents navigation, explains desktop-only local paths and never infers File.name", async () => {
+	const f = await fixture({ desktop: false });
+	const transfer = f.transfer([f.file("/not/a/backing/path.pdf")]);
+	const enter = await f.event("dragenter", transfer);
+	assert.equal(enter.defaultPrevented, true);
+	assert.match(f.doc.querySelector('[data-testid="file-path-drop-indicator"]')!.textContent!, /desktop app/);
+	const over = await f.event("dragover", transfer);
+	assert.equal(over.defaultPrevented, true);
+	assert.equal(transfer.dropEffect, "copy");
+	const drop = await f.event("drop", transfer);
+	assert.equal(drop.defaultPrevented, true);
+	assert.match(f.status, /Local file paths can only be attached in the desktop app/);
+	assert.match(f.status, /paste a full path instead/);
+	assert.equal(f.doc.querySelector('[data-testid="file-path-drop-indicator"]'), null);
+	assert.equal(f.value, "readthis");
+	assert.deepEqual(f.appends, []);
+	assert.deepEqual(f.resolved, []);
+	f.assertPathOnly();
+});
+
+test("invalid, virtual and directory items are skipped while valid backing paths stay ordered", async () => {
+	const f = await fixture();
+	const files = [
+		f.file("virtual.pdf"), f.file("bad.pdf", "relative.pdf"), f.file("broken.pdf", new Error("not backed")),
+		f.file("folder", "/directory"), f.file("valid.pdf", "/existing/valid.pdf"),
+		f.file("multiline.pdf", "/a\nb.pdf"), f.file("NUL.pdf", "/a\0b.pdf"), f.file("url.pdf", "file:///a.pdf"),
+	];
+	await f.event("drop", f.transfer(files, [3]));
+	assert.deepEqual(f.appends, ["`/existing/valid.pdf`"]);
+	assert.equal(f.resolved.includes(files[3]!), false, "directory metadata prevents resolving a folder");
+	assert.match(f.status, /Some dropped items had no available file path/);
+	f.assertPathOnly();
+});
+
+test("a drop with no backing paths or no destination has a truthful notice and stages nothing", async () => {
+	const f = await fixture({ claimed: false });
+	const missing = await f.event("drop", f.transfer([f.file("virtual.pdf")]));
+	assert.equal(missing.defaultPrevented, true);
+	assert.match(f.status, /No local file paths were available/);
+	await f.event("drop", f.transfer([f.file("valid.pdf", "/existing/valid.pdf")]));
+	assert.match(f.status, /Open a chat to attach file paths/);
+	assert.deepEqual(f.appends, []);
+	assert.equal(f.value, "readthis");
+	f.assertPathOnly();
+});
+
+test("non-file drags stay native; sidebar file drops prevent navigation without attaching", async () => {
+	const f = await fixture();
+	const plain = f.transfer([], [], ["text/plain"]);
+	for (const type of ["dragenter", "dragover", "drop"]) {
+		assert.equal((await f.event(type, plain)).defaultPrevented, false);
+	}
+	const sidebar = f.doc.querySelector('[data-testid="sidebar"]')!;
+	assert.equal((await f.event("drop", f.transfer([f.file("notes.pdf", "/existing/notes.pdf")]), sidebar)).defaultPrevented, true);
+	assert.deepEqual(f.resolved, []);
+	assert.deepEqual(f.appends, []);
+	assert.equal(f.status, "");
+	f.assertPathOnly();
+});
+
+test("nested enter/leave depth keeps the drop overlay until the zone is left; notice is dismissible", async () => {
+	const f = await fixture({ desktop: false });
+	const transfer = f.transfer([f.file("notes.pdf")]);
+	await f.event("dragenter", transfer);
+	await f.event("dragenter", transfer);
+	await f.event("dragleave", transfer);
+	assert.ok(f.doc.querySelector('[data-testid="file-path-drop-indicator"]'));
+	await f.event("dragleave", transfer);
+	assert.equal(f.doc.querySelector('[data-testid="file-path-drop-indicator"]'), null);
+	await f.event("drop", transfer);
+	assert.notEqual(f.status, "");
+	await act(async () => { f.doc.querySelector<HTMLElement>('[aria-label="Dismiss attachment notice"]')!.click(); });
+	assert.equal(f.status, "");
+	f.assertPathOnly();
+});
+
+test("production AppShell places the sidebar outside its content-only drop zone", () => {
+	const source = readFileSync(new URL("../components/sidebar.tsx", import.meta.url), "utf8");
+	const shell = source.slice(source.indexOf("export function AppShell("));
+	assert.match(shell, /<SessionsSidebar\s*\/>\s*<FilePathDropZone\b[^>]*>\{children\}<\/FilePathDropZone>/);
+	assert.doesNotMatch(shell, /<FilePathDropZone\b[^>]*>[\s\S]*<SessionsSidebar/);
+});

tests/file-path-preload.test.ts

@@ -0,0 +1,93 @@
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { describe, it } from "node:test";
+import { runInNewContext } from "node:vm";
+
+interface PathBridge {
+	platform: string;
+	getPathForFile(file: unknown): string;
+	[key: string]: unknown;
+}
+
+/** Execute the actual preload in a VM, without Electron, IPC or app startup. */
+function fixture(resolve: (file: unknown) => string) {
+	let bridge!: PathBridge;
+	const supplied: unknown[] = [];
+	const sent: unknown[][] = [];
+	const invoked: unknown[][] = [];
+	const imports: string[] = [];
+	const exposed: string[] = [];
+	const electron = {
+		contextBridge: { exposeInMainWorld(name: string, surface: PathBridge) { exposed.push(name); bridge = surface; } },
+		webUtils: { getPathForFile(file: unknown) { supplied.push(file); return resolve(file); } },
+		ipcRenderer: {
+			on() {}, removeListener() {},
+			send: (...args: unknown[]) => { sent.push(args); },
+			invoke: (...args: unknown[]) => { invoked.push(args); return Promise.resolve(); },
+		},
+	};
+	runInNewContext(readFileSync(new URL("../electron/preload.cjs", import.meta.url), "utf8"), {
+		process: { platform: "darwin", argv: [] },
+		require: (name: string) => { imports.push(name); assert.equal(name, "electron"); return electron; },
+	});
+	return { bridge, supplied, sent, invoked, imports, exposed, electron };
+}
+
+describe("path-only preload bridge", () => {
+	it("forwards the exact supplied File identity to webUtils, returning only the backing path without IPC", () => {
+		const file = new File(["synthetic fixture"], "display-name.pdf", { type: "application/pdf" });
+		let reads = 0;
+		for (const method of ["text", "arrayBuffer", "stream"] as const) {
+			Object.defineProperty(file, method, { value: () => { reads++; throw new Error("Must not read file content"); } });
+		}
+		const fullPath = "/actual/course/notes with `backticks`.pdf";
+		const f = fixture((supplied) => { assert.equal(supplied, file); return fullPath; });
+		assert.deepEqual(f.exposed, ["lh"]);
+		assert.deepEqual(f.imports, ["electron"]);
+		assert.equal(f.bridge.getPathForFile(file), fullPath);
+		assert.equal(f.supplied.length, 1);
+		assert.equal(f.supplied[0], file);
+		assert.notEqual(fullPath, file.name);
+		assert.equal(reads, 0);
+		assert.deepEqual(f.sent, []);
+		assert.deepEqual(f.invoked, []);
+	});
+
+	it("keeps Electron's empty result for a File without an OS backing path, never substituting its name", () => {
+		const virtual = new File(["virtual"], "/misleading/full/path.pdf");
+		const f = fixture(() => "");
+		assert.equal(f.bridge.getPathForFile(virtual), "");
+		assert.equal(f.supplied[0], virtual);
+		assert.deepEqual(f.sent, []);
+		assert.deepEqual(f.invoked, []);
+	});
+
+	it("preserves webUtils errors for invalid File arguments instead of inventing a path", () => {
+		const invalid = { name: "/misleading/filename.pdf", path: "/not/a/capability.pdf" };
+		const error = new TypeError("Expected a File");
+		const f = fixture((supplied) => { assert.equal(supplied, invalid); throw error; });
+		assert.throws(() => f.bridge.getPathForFile(invalid), (caught) => caught === error);
+		assert.equal(f.supplied[0], invalid);
+		assert.deepEqual(f.sent, []);
+		assert.deepEqual(f.invoked, []);
+	});
+
+	it("adds just the narrow path resolver to the explicit surface, without exposing Electron or filesystem APIs", () => {
+		const f = fixture(() => "");
+		assert.deepEqual(Object.keys(f.bridge).sort(), [
+			"chatgpt", "checkForUpdates", "expandWindow", "getPathForFile", "getUpdateState", "getZoom",
+			"installUpdate", "onOpenSettings", "onUpdateStatus", "onZoom", "platform", "subscriptions",
+		]);
+		assert.equal(f.bridge.platform, "darwin");
+		for (const name of ["webUtils", "ipcRenderer", "electron", "fs", "require", "readFile", "writeFile", "uploadFile", "openPath"]) {
+			assert.equal(Object.hasOwn(f.bridge, name), false, name);
+		}
+		assert.notEqual(f.bridge.getPathForFile, f.electron.webUtils.getPathForFile, "webUtils itself is not exposed");
+	});
+
+	it("retains context isolation, sandbox and disabled Node integration in the production window", () => {
+		const main = readFileSync(new URL("../electron/main.cjs", import.meta.url), "utf8");
+		assert.match(main, /webPreferences:\s*\{\s*contextIsolation:\s*true,\s*sandbox:\s*true,\s*nodeIntegration:\s*false,/);
+		assert.match(main, /preload:\s*path\.join\(__dirname,\s*"preload\.cjs"\)/);
+	});
+});

tests/file-paths.test.ts

@@ -0,0 +1,127 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import { filePathLabel, parseFilePaths, quoteFilePath } from "../src/core/file-paths.ts";
+
+function paths(text: string) {
+	return parseFilePaths(text).flatMap((part) => part.kind === "path" ? [part.path] : []);
+}
+
+function assertLossless(text: string) {
+	const parts = parseFilePaths(text);
+	assert.equal(parts.map((part) => part.text).join(""), text);
+	let offset = 0;
+	for (const part of parts) {
+		assert.equal(part.start, offset);
+		assert.equal(text.slice(part.start, part.end), part.text);
+		offset = part.end;
+	}
+	assert.equal(offset, text.length);
+}
+
+describe("plain-text file path tokens", () => {
+	it("returns typed tokens with exact original text and UTF-16 offsets", () => {
+		const text = "📚 Read `/tmp/my notes.pdf` now.";
+		assert.deepEqual(parseFilePaths(text), [
+			{ kind: "text", text: "📚 Read ", start: 0, end: 8 },
+			{ kind: "path", text: "`/tmp/my notes.pdf`", path: "/tmp/my notes.pdf", start: 8, end: 27 },
+			{ kind: "text", text: " now.", start: 27, end: 32 },
+		]);
+		assert.deepEqual(parseFilePaths(""), []);
+	});
+
+	it("accepts rooted POSIX, drive, UNC and home paths without filesystem access", () => {
+		for (const path of [
+			"/tmp/notes.pdf", "/", "/does not exist/α ∂ 🧠.pdf", "//volume/file",
+			"C:\\Users\\Learner\\My notes.pdf", "d:/notes/測度.md", "C:\\",
+			"\\\\server\\share\\nested folder\\notes.pdf", "\\\\server\\share", "\\\\server/share/file.txt",
+			"~/Documents/notes.pdf", "~/", "/tmp/a\\b.txt", "/tmp/<>&\"'[]()#?!;:$*=|.txt",
+		]) {
+			const quoted = quoteFilePath(path);
+			assert.deepEqual(paths(quoted), [path]);
+			assertLossless(quoted);
+		}
+	});
+
+	it("recognizes manual and pasted quoted paths anywhere, including adjacent prose", () => {
+		const text = "word`/a`word (`~/b`) [`C:/c`](x) <`/d`> /not/quoted";
+		assert.deepEqual(paths(text), ["/a", "~/b", "C:/c", "/d"]);
+		assertLossless(text);
+	});
+
+	it("does not reinterpret ordinary prose, relative paths, URLs or code", () => {
+		for (const text of [
+			"Read /tmp/file.pdf and ~/notes", "`hello world`", "`a + b`", "`notes.pdf`", "`./notes.pdf`",
+			"`../notes.pdf`", "`C:notes.pdf`", "`~someone/notes.pdf`", "`file:///tmp/notes.pdf`",
+			"`https://example.test/a.pdf`", "`\\notes.pdf`", "`\\\\server`", "`const p = '/a';`",
+			"` /leading space`", "``code `/a` here``", "```\n/a\n```", "```\n`/a`\n```",
+		]) {
+			assert.deepEqual(paths(text), [], text);
+			assertLossless(text);
+		}
+	});
+
+	it("matches complete equal delimiter runs, never their partial boundaries", () => {
+		for (const text of ["`/a", "``/a`", "`/a``", "```/a``"]) {
+			assert.deepEqual(paths(text), []);
+			assertLossless(text);
+		}
+		// Other-width runs are legal filename characters, not partial closers.
+		assert.deepEqual(paths("``/a```/b``"), ["/a```/b"]);
+		assert.deepEqual(paths("`/a``/b`"), ["/a``/b"]);
+		assert.deepEqual(paths("``not code closed? `/a`"), ["/a"]);
+		assert.deepEqual(paths("```/a```"), ["/a"]);
+	});
+
+	it("preserves backticks with variable delimiters and one-space padding", () => {
+		assert.equal(quoteFilePath("/tmp/a`b.txt"), "``/tmp/a`b.txt``");
+		assert.equal(quoteFilePath("/tmp/a`"), "`` /tmp/a` ``");
+		assert.equal(quoteFilePath("/tmp/a```"), "```` /tmp/a``` ````");
+		for (const path of ["/tmp/a`", "/tmp/a``b`", "/tmp/`/```/``", "/tmp/a `", "/tmp/a  ", "/tmp/ "]) {
+			const text = `before ${quoteFilePath(path)} after`;
+			assert.deepEqual(paths(text), [path]);
+			assertLossless(text);
+		}
+		assert.deepEqual(paths("`` /tmp/a` ``"), ["/tmp/a`"]);
+		assert.deepEqual(paths("` /tmp/a  `"), ["/tmp/a "]);
+		assert.deepEqual(paths("`  /tmp/a  `"), [], "strip one padding space only");
+	});
+
+	it("rejects all C0/C1 controls, multiline paths and Unicode line separators", () => {
+		const controls = [
+			...Array.from({ length: 32 }, (_, i) => String.fromCharCode(i)),
+			...Array.from({ length: 33 }, (_, i) => String.fromCharCode(127 + i)),
+			"\u2028", "\u2029",
+		];
+		for (const control of controls) {
+			const path = `/tmp/a${control}b.pdf`;
+			assert.deepEqual(paths(`\`${path}\``), []);
+			assert.throws(() => quoteFilePath(path), TypeError);
+		}
+		for (const path of ["", "relative", "file:///tmp/a", "C:a", "\\\\server"]) {
+			assert.throws(() => quoteFilePath(path), TypeError);
+		}
+	});
+
+	it("round-trips many combinations of legal filename punctuation and whitespace", () => {
+		for (const piece of ["`", "``", " ``` ", " ", "  ", "<script>", "[link](x)", "a\\b", "Ω📚"]) {
+			for (const suffix of ["", "`", "``", " ", ".pdf"]) {
+				const path = `/tmp/${piece}${suffix}`;
+				const quoted = quoteFilePath(path);
+				assert.deepEqual(paths(quoted), [path]);
+				assertLossless(quoted);
+			}
+		}
+	});
+});
+
+describe("filePathLabel", () => {
+	it("extracts basenames for each platform without normalizing the path", () => {
+		for (const [path, label] of [
+			["/tmp/a.pdf", "a.pdf"], ["~/測度 theory.md", "測度 theory.md"],
+			["C:\\Users\\a.pdf", "a.pdf"], ["C:/Users/a.pdf", "a.pdf"],
+			["\\\\server\\share\\a.pdf", "a.pdf"], ["/tmp/a\\b.txt", "a\\b.txt"],
+			["/tmp/folder/", "folder"], ["/", "/"], ["~/", "~/"], ["C:\\", "C:\\"],
+			["/tmp/a`b", "a`b"],
+		]) assert.equal(filePathLabel(path!), label);
+	});
+});

tests/path-input.test.tsx

@@ -0,0 +1,491 @@
+import React, { act } from "react";
+import assert from "node:assert/strict";
+import { afterEach, test } from "node:test";
+import { parseHTML } from "linkedom";
+import { renderToStaticMarkup } from "react-dom/server";
+import { PathInput, INSERT_FILE_PATHS_EVENT } from "../components/path-input.tsx";
+import {
+	PATH_CARET_ATTRIBUTE, PATH_SOURCE_ATTRIBUTE, PathInputHistory, adjacentPathRange, atomicPathRange,
+	insertFilePaths, normalizePathEdit, normalizePathInputValue, pathInputOffset, pathInputPoint, readPathInput,
+	readPathSelection, renderPathInput, replacePathSelection, restorePathSelection,
+} from "../components/path-input-dom.ts";
+import { quoteFilePath } from "../src/core/file-paths.ts";
+
+function editor() {
+	const { document } = parseHTML("<html><body><div id='editor'></div></body></html>");
+	return document.getElementById("editor")!;
+}
+
+test("DOM projection is lossless across whitespace, Unicode and all rooted path forms", () => {
+	const root = editor();
+	const paths = ["/a/notes one.pdf", "C:\\a\\notes.pdf", "\\\\host\\share\\sheet.csv", "~/notes`final`.pdf"];
+	const value = `  👩🏽‍💻\t中\n${paths.map(quoteFilePath).join("\n\t")}\n \n`;
+	const hosts = renderPathInput(root, value);
+	assert.equal(hosts.length, paths.length);
+	for (const { host } of hosts) {
+		host.textContent = "abbreviated.pdf";
+		assert.equal(host.getAttribute("contenteditable"), "false");
+	}
+	assert.equal(readPathInput(root), value);
+	assert.equal(root.dataset.empty, "false");
+	renderPathInput(root, "");
+	assert.equal(readPathInput(root), "");
+	assert.equal(root.dataset.empty, "true");
+});
+
+test("logical offsets round-trip across text, adjacent chips, line breaks and reversed selections", () => {
+	const root = editor();
+	const value = `🙂A ${quoteFilePath("/one")} ${quoteFilePath("/two")}\nend`;
+	renderPathInput(root, value);
+	for (let offset = 0; offset <= value.length; offset++) {
+		const point = pathInputPoint(root, offset);
+		const mapped = pathInputOffset(root, point.node, point.offset)!;
+		const token = Array.from(root.querySelectorAll(`[${PATH_SOURCE_ATTRIBUTE}]`)).find((host) => {
+			const start = value.indexOf(host.getAttribute(PATH_SOURCE_ATTRIBUTE)!);
+			return offset > start && offset < start + host.getAttribute(PATH_SOURCE_ATTRIBUTE)!.length;
+		});
+		if (!token) assert.equal(mapped, offset, `offset ${offset}`);
+		else {
+			const raw = token.getAttribute(PATH_SOURCE_ATTRIBUTE)!;
+			const start = value.indexOf(raw);
+			assert.ok(mapped === start || mapped === start + raw.length);
+		}
+	}
+	assert.equal(pathInputOffset(root, root.ownerDocument.body, 0), null);
+});
+
+test("BR/block fallback never reads visual labels or normalizes ordinary spaces", () => {
+	const root = editor();
+	root.innerHTML = "<div> a  </div><div><br></div><div>b</div>";
+	assert.equal(readPathInput(root), " a  \n\nb");
+	root.innerHTML = "<br>";
+	assert.equal(readPathInput(root), "");
+	root.innerHTML = "a<br>b";
+	assert.equal(readPathInput(root), "a\nb");
+});
+
+test("trailing newline caret placeholder is presentation-only and logical end maps before it", () => {
+	const root = editor();
+	for (const value of ["\n", "\n\n", "one\n", "one\n\n", "one\n\n\n"]) {
+		renderPathInput(root, value);
+		assert.equal(root.querySelectorAll(`[${PATH_CARET_ATTRIBUTE}]`).length, 1);
+		assert.equal(root.lastElementChild?.tagName, "BR");
+		assert.equal(root.lastElementChild?.getAttribute("aria-hidden"), "true");
+		assert.equal(root.textContent, value);
+		assert.equal(readPathInput(root), value);
+		const point = pathInputPoint(root, value.length);
+		assert.equal(point.node, root);
+		assert.equal(point.offset, root.childNodes.length - 1);
+		assert.equal(pathInputOffset(root, point.node, point.offset), value.length);
+		assert.equal(pathInputOffset(root, root.lastChild!, 0), value.length);
+	}
+	for (const value of ["", "one", "one\ntwo"]) {
+		renderPathInput(root, value);
+		assert.equal(root.querySelector(`[${PATH_CARET_ATTRIBUTE}]`), null);
+		assert.equal(readPathInput(root), value);
+	}
+});
+
+test("range replacement/deletion is atomic and leaves neighboring whitespace untouched", () => {
+	const token = quoteFilePath("/course/notes.pdf");
+	const value = `a ${token} b`;
+	assert.deepEqual(atomicPathRange(value, { anchor: 5, focus: 1 }), { start: 1, end: 2 + token.length });
+	assert.equal(replacePathSelection(value, { anchor: 3, focus: 8 }, "").value, "a  b");
+	assert.deepEqual(adjacentPathRange(value, { anchor: 2, focus: 2 }, "forward"), { anchor: 2, focus: 2 + token.length });
+	assert.deepEqual(adjacentPathRange(value, { anchor: 2 + token.length, focus: 2 + token.length }, "backward"), { anchor: 2, focus: 2 + token.length });
+	assert.equal(adjacentPathRange(value, { anchor: 1, focus: 1 }, "forward"), null);
+});
+
+test("file insertion uses full quoted sources at saved ranges with separating spaces", () => {
+	const next = insertFilePaths("readthis", { anchor: 4, focus: 4 }, ["/a b.pdf", "C:\\a\\x.txt"]);
+	assert.equal(next.value, "read `/a b.pdf` `C:\\a\\x.txt` this");
+	assert.equal(next.selection.anchor, next.value.length - 4);
+	assert.equal(insertFilePaths("a\n", { anchor: 2, focus: 2 }, ["~/x"]).value, "a\n`~/x`");
+	assert.throws(() => insertFilePaths("", { anchor: 0, focus: 0 }, ["relative.txt"]), TypeError);
+});
+
+test("owned history restores values and directional selections; a new edit discards redo", () => {
+	const history = new PathInputHistory();
+	const a = { value: "a", selection: { anchor: 1, focus: 0 } };
+	const b = { value: "ab", selection: { anchor: 2, focus: 2 } };
+	history.push(a);
+	assert.deepEqual(history.undo(b), a);
+	assert.deepEqual(history.redo(a), b);
+	history.undo(b);
+	history.push(a);
+	assert.equal(history.redo(b), null);
+	history.reset();
+	assert.equal(history.undo(b), null);
+});
+
+test("textbox exposes accessibility, placeholder, global-drop markers and requested sizing", () => {
+	const html = renderToStaticMarkup(<PathInput value="" onValueChange={() => {}} placeholder="Ask" aria-label="Message" defaultDropTarget className="min-h-24 max-h-64" />);
+	for (const pattern of [/role="textbox"/, /aria-multiline="true"/, /aria-label="Message"/, /data-file-path-input=""/, /data-file-path-default=""/, /data-placeholder="Ask"/, /min-h-24 max-h-64/]) assert.match(html, pattern);
+});
+
+test("SSR preserves the full escaped initial draft without waiting for client effects", () => {
+	const draft = "  Restored <reasoning> & notes\n`/course/full notes.pdf`\n ";
+	const html = renderToStaticMarkup(<PathInput value={draft} onValueChange={() => assert.fail("SSR cannot emit changes")} placeholder="Reasoning" />);
+	const { document } = parseHTML(`<html><body>${html}</body></html>`);
+	const field = document.querySelector('[data-file-path-input]')!;
+	assert.equal(field.textContent, draft);
+	assert.equal(field.getAttribute("contenteditable") ?? field.getAttribute("contentEditable"), "true");
+	assert.equal(field.getAttribute("data-empty"), "false");
+	assert.equal(field.querySelector("reasoning"), null);
+	assert.match(html, /&lt;reasoning&gt;/);
+	const single = renderToStaticMarkup(<PathInput singleLine value={"one\r\ntwo"} onValueChange={() => {}} />);
+	assert.equal(parseHTML(`<html><body>${single}</body></html>`).document.body.textContent, "onetwo");
+});
+
+test("textbox accessible name falls back to placeholder and preserves explicit aria-label", () => {
+	const fallback = renderToStaticMarkup(<PathInput value="" onValueChange={() => {}} placeholder="Your reasoning" />);
+	assert.match(fallback, /aria-label="Your reasoning"/);
+	const explicit = renderToStaticMarkup(<PathInput value="" onValueChange={() => {}} placeholder="Your reasoning" aria-label="Custom answer" />);
+	assert.match(explicit, /aria-label="Custom answer"/);
+	assert.doesNotMatch(explicit, /aria-label="Your reasoning"/);
+});
+
+let cleanup: (() => Promise<void>) | undefined;
+afterEach(async () => { await cleanup?.(); cleanup = undefined; });
+
+/** linkedom has no Selection/default editing actions. The shim tests our offset
+ * contract, NOT browser caret navigation or the native IME implementation. */
+async function fixture(initial: string, singleLine = false) {
+	const { window: win, document: doc } = parseHTML("<html><body><div id='root'></div><button id='elsewhere'></button></body></html>");
+	let active: Element = doc.body;
+	Object.defineProperty(doc, "activeElement", { get: () => active });
+	const selection = {
+		anchorNode: null as Node | null, anchorOffset: 0, focusNode: null as Node | null, focusOffset: 0,
+		setBaseAndExtent(anchorNode: Node, anchorOffset: number, focusNode: Node, focusOffset: number) {
+			Object.assign(this, { anchorNode, anchorOffset, focusNode, focusOffset });
+		},
+	};
+	Object.assign(doc, { getSelection: () => selection, oninput: null });
+	win.HTMLElement.prototype.focus = function () { active = this; };
+	const previous = new Map<string, PropertyDescriptor | undefined>();
+	for (const [name, value] of Object.entries({ React, window: win, document: doc, HTMLElement: win.HTMLElement, Element: win.Element, Event: win.Event, IS_REACT_ACT_ENVIRONMENT: true })) {
+		previous.set(name, Object.getOwnPropertyDescriptor(globalThis, name));
+		Object.defineProperty(globalThis, name, { configurable: true, writable: true, value });
+	}
+	const { createRoot } = await import("react-dom/client");
+	const reactRoot = createRoot(doc.getElementById("root")!);
+	const ref = React.createRef<HTMLDivElement>();
+	let value = initial;
+	const writes: string[] = [];
+	let keys = 0;
+	function draw() {
+		reactRoot.render(<PathInput ref={ref} singleLine={singleLine} value={value} onValueChange={(next) => { writes.push(next); value = next; draw(); }} onKeyDown={() => { keys++; }} />);
+	}
+	await act(async () => { draw(); });
+	cleanup = async () => {
+		await act(async () => { reactRoot.unmount(); });
+		for (const [name, descriptor] of previous) {
+			if (descriptor) Object.defineProperty(globalThis, name, descriptor);
+			else delete (globalThis as Record<string, unknown>)[name];
+		}
+	};
+	const root = ref.current!;
+	root.focus();
+	function select(anchor: number, focus = anchor) {
+		restorePathSelection(root, { anchor, focus });
+		doc.dispatchEvent(new win.Event("selectionchange"));
+	}
+	async function event(type: string, properties: Record<string, unknown> = {}) {
+		const event = new win.Event(type, { bubbles: true, cancelable: true });
+		Object.assign(event, properties);
+		await act(async () => { root.dispatchEvent(event); });
+		return event;
+	}
+	return {
+		root, doc, select, event, writes, selection,
+		get value() { return value; }, get keys() { return keys; },
+		async external(next: string) { await act(async () => { value = next; draw(); }); },
+		async nativeText(next: string, inputType = "insertText") {
+			await event("beforeinput", { inputType, isComposing: false });
+			root.replaceChildren(doc.createTextNode(next));
+			select(next.length);
+			await event("input", { inputType });
+		},
+	};
+}
+
+test("native typing, token insertion/deletion and undo/redo share one history", async () => {
+	const f = await fixture("a");
+	f.select(1);
+	await f.nativeText("ab");
+	await f.event(INSERT_FILE_PATHS_EVENT, { detail: ["/notes.pdf"] });
+	assert.equal(f.value, "ab `/notes.pdf`");
+	assert.match(f.root.textContent!, /notes.pdf/);
+	await f.event("keydown", { key: "Backspace" });
+	assert.equal(f.value, "ab ");
+	await f.event("keydown", { key: "z", metaKey: true });
+	assert.equal(f.value, "ab `/notes.pdf`");
+	await f.event("keydown", { key: "z", metaKey: true });
+	assert.equal(f.value, "ab");
+	await f.event("keydown", { key: "z", metaKey: true });
+	assert.equal(f.value, "a");
+	await f.event("beforeinput", { inputType: "historyRedo" });
+	assert.equal(f.value, "ab");
+});
+
+test("immutable SSR fallback never stomps native edits, controlled updates, chips or reset", async () => {
+	const initial = "Restored draft `/course/original.pdf`";
+	const f = await fixture(initial);
+	assert.equal(readPathInput(f.root), initial);
+	assert.equal(f.root.querySelectorAll(`[${PATH_SOURCE_ATTRIBUTE}]`).length, 1);
+	f.select(initial.length);
+	await f.nativeText("New typed draft");
+	assert.equal(readPathInput(f.root), "New typed draft");
+	assert.equal(f.root.textContent, "New typed draft");
+	await f.external("Controlled `/course/replaced.pdf`");
+	assert.equal(readPathInput(f.root), "Controlled `/course/replaced.pdf`");
+	assert.equal(f.root.querySelectorAll(`[${PATH_SOURCE_ATTRIBUTE}]`).length, 1);
+	assert.doesNotMatch(f.root.textContent!, /Restored draft/);
+	await f.external("");
+	await f.external(""); // Re-render again with the same initial fallback child prop.
+	assert.equal(readPathInput(f.root), "");
+	assert.equal(f.root.textContent, "");
+	assert.equal(f.root.dataset.empty, "true");
+});
+
+test("external dictation append/reset and drop at an unfocused saved selection", async () => {
+	const f = await fixture("one two");
+	f.select(3);
+	f.doc.getElementById("elsewhere")!.focus();
+	await f.event(INSERT_FILE_PATHS_EVENT, { detail: ["/notes one.pdf"] });
+	assert.equal(f.value, "one `/notes one.pdf` two");
+	assert.equal(f.doc.activeElement, f.root);
+	assert.equal(f.keys, 0, "staging must not submit");
+	f.select(f.value.length);
+	await f.external(`${f.value}\nspoken words`);
+	assert.equal(readPathInput(f.root), f.value);
+	await f.event("keydown", { key: "z", ctrlKey: true });
+	assert.equal(f.value, "one `/notes one.pdf` two");
+	await f.external("");
+	assert.equal(readPathInput(f.root), "");
+	await f.event("keydown", { key: "z", ctrlKey: true });
+	assert.equal(f.value, "");
+});
+
+test("plaintext paste ignores HTML and copy/cut use full token source in either direction", async () => {
+	const source = "read `/deep/course/notes.pdf` now";
+	const f = await fixture(source);
+	f.select(source.length - 4, 5);
+	const clipboard = new Map<string, string>();
+	const clipboardData = { setData: (type: string, text: string) => clipboard.set(type, text), getData: (type: string) => type === "text/plain" ? "<img src=x onerror=alert(1)>\n中" : "<b>unsafe HTML</b>" };
+	await f.event("copy", { clipboardData });
+	assert.equal(clipboard.get("text/plain"), "`/deep/course/notes.pdf`");
+	await f.event("cut", { clipboardData });
+	assert.equal(f.value, "read  now");
+	f.select(5);
+	await f.event("paste", { clipboardData });
+	assert.equal(f.value, "read <img src=x onerror=alert(1)>\n中 now");
+	assert.equal(f.root.querySelector("img"), null);
+	assert.equal(readPathInput(f.root), f.value);
+});
+
+test("image/file-only paste prevents native insertion without deleting selected text or chips", async () => {
+	const source = "plain `/course/notes.pdf` end";
+	const f = await fixture(source);
+	const clipboardData = { types: ["Files", "image/png"], getData: () => "" };
+	for (const [anchor, focus] of [[0, 5], [6, source.length - 4]]) {
+		f.select(anchor!, focus!);
+		const paste = await f.event("paste", { clipboardData });
+		assert.equal(paste.defaultPrevented, true);
+		assert.equal(f.value, source);
+		assert.equal(readPathInput(f.root), source);
+	}
+	assert.deepEqual(f.writes, []);
+	assert.equal(f.root.querySelectorAll(`[${PATH_SOURCE_ATTRIBUTE}]`).length, 1);
+});
+
+test("empty clipboard text stays a no-op before, during and after IME with a chip selected", async () => {
+	const source = "a `/course/notes.pdf` z";
+	const f = await fixture(source);
+	f.select(2, source.length - 2);
+	const clipboardData = { getData: () => "", types: ["text/html"] };
+	await f.event("paste", { clipboardData });
+	await f.event("compositionstart");
+	const during = await f.event("paste", { clipboardData });
+	assert.equal(during.defaultPrevented, true);
+	assert.equal(readPathInput(f.root), source);
+	await f.event("compositionend");
+	assert.equal(readPathInput(f.root), source, "no empty pending paste can remove the selected chip");
+	await f.event("paste", { clipboardData });
+	assert.equal(f.value, source);
+	assert.deepEqual(f.writes, []);
+});
+
+test("Shift+Delete delegates to cut, preserving full-source clipboard and deleting only once", async () => {
+	const f = await fixture("plain`/next.pdf`");
+	for (const [source, selected] of [["plain`/next.pdf`", "plain"], ["`/course/notes.pdf` `/next.pdf`", "`/course/notes.pdf` "]] as const) {
+		await f.external(source);
+		f.select(0, selected.length);
+		const key = await f.event("keydown", { key: "Delete", shiftKey: true });
+		assert.equal(key.defaultPrevented, false, "native Cut shortcut must reach the browser");
+		assert.equal(f.value, source, "keydown alone must not delete the selection");
+		let copied = "";
+		const cut = await f.event("cut", { clipboardData: { setData: (type: string, value: string) => { assert.equal(type, "text/plain"); copied = value; } } });
+		assert.equal(cut.defaultPrevented, true);
+		assert.equal(copied, selected);
+		assert.equal(f.value, "`/next.pdf`");
+		const beforeInput = await f.event("beforeinput", { inputType: "deleteByCut" });
+		assert.equal(beforeInput.defaultPrevented, true);
+		assert.equal(f.value, "`/next.pdf`", "a trailing deleteByCut must not delete the neighboring chip");
+	}
+});
+
+test("copying even a partial visual chip label copies its complete source", async () => {
+	const f = await fixture("read `/deep/course/notes.pdf` now");
+	const label = f.root.querySelector(`[${PATH_SOURCE_ATTRIBUTE}] [role=img] span`)!.firstChild!;
+	f.selection.setBaseAndExtent(label, 1, label, 3);
+	f.doc.dispatchEvent(new window.Event("selectionchange"));
+	let copied = "";
+	await f.event("copy", { clipboardData: { setData: (_type: string, value: string) => { copied = value; } } });
+	assert.equal(copied, "`/deep/course/notes.pdf`");
+});
+
+test("composition keeps native DOM untouched, emits once, and suppresses consumer Enter", async () => {
+	const f = await fixture("hello ");
+	f.select(6);
+	await f.event("compositionstart");
+	f.root.replaceChildren(f.doc.createTextNode("hello 中"));
+	f.select(7);
+	await f.event("input", { isComposing: true });
+	await f.event("keydown", { key: "Enter", keyCode: 229, isComposing: true });
+	assert.equal(f.writes.length, 0);
+	assert.equal(f.keys, 0);
+	assert.equal(readPathInput(f.root), "hello 中");
+	await f.event("compositionend");
+	assert.deepEqual(f.writes, ["hello 中"]);
+	await f.event("keydown", { key: "z", metaKey: true });
+	assert.equal(f.value, "hello ");
+});
+
+test("Enter inserts a literal newline and range deletion spans text and complete chips", async () => {
+	const f = await fixture("a `/one.pdf` b");
+	f.select(f.value.length);
+	await f.event("beforeinput", { inputType: "insertParagraph" });
+	assert.equal(f.value, "a `/one.pdf` b\n");
+	f.select(1, f.value.length - 1);
+	await f.event("keydown", { key: "Delete" });
+	assert.equal(f.value, "a\n");
+	assert.equal(readPathInput(f.root), "a\n");
+});
+
+test("multiple trailing newlines preserve selection and survive native Backspace plus undo/redo", async () => {
+	const f = await fixture("one\n\n");
+	f.select(f.value.length, 1);
+	assert.deepEqual(readPathSelection(f.root), { anchor: 5, focus: 1 });
+	f.select(f.value.length);
+	assert.equal(f.selection.focusNode, f.root);
+	assert.equal(f.root.lastElementChild?.hasAttribute(PATH_CARET_ATTRIBUTE), true);
+	// linkedom has no default Backspace action; model the native text deletion.
+	await f.nativeText("one\n", "deleteContentBackward");
+	assert.equal(f.value, "one\n");
+	assert.equal(readPathInput(f.root), f.value);
+	assert.equal(f.root.querySelectorAll(`[${PATH_CARET_ATTRIBUTE}]`).length, 1);
+	await f.event("keydown", { key: "z", metaKey: true });
+	assert.equal(f.value, "one\n\n");
+	assert.deepEqual(readPathSelection(f.root), { anchor: 5, focus: 5 });
+	assert.equal(f.root.querySelectorAll(`[${PATH_CARET_ATTRIBUTE}]`).length, 1);
+	await f.event("keydown", { key: "z", metaKey: true, shiftKey: true });
+	assert.equal(f.value, "one\n");
+	assert.deepEqual(readPathSelection(f.root), { anchor: 4, focus: 4 });
+	await f.external("");
+	assert.equal(f.root.dataset.empty, "true");
+	assert.equal(f.root.querySelector(`[${PATH_CARET_ATTRIBUTE}]`), null);
+});
+
+test("single-line mode never adds a trailing newline caret placeholder", async () => {
+	const f = await fixture("one\n\n", true);
+	assert.equal(readPathInput(f.root), "one");
+	assert.equal(f.root.querySelector(`[${PATH_CARET_ATTRIBUTE}]`), null);
+});
+
+test("paste during IME stays plaintext and is deferred until composition finishes", async () => {
+	const f = await fixture("");
+	f.select(0);
+	await f.event("compositionstart");
+	f.root.replaceChildren(f.doc.createTextNode("中"));
+	f.select(1);
+	await f.event("input", { isComposing: true });
+	assert.equal(f.root.dataset.empty, "false", "placeholder hides without normalizing the composing DOM");
+	const paste = await f.event("paste", { clipboardData: { getData: () => "<b>plain</b>" } });
+	assert.equal(paste.defaultPrevented, true);
+	assert.equal(readPathInput(f.root), "中");
+	assert.equal(f.writes.length, 0);
+	await f.event("compositionend");
+	assert.equal(f.value, "中<b>plain</b>");
+	assert.equal(f.root.querySelector("b"), null);
+});
+
+test("single-line normalization strips only CR/LF and remaps directional UTF-16 selections", () => {
+	const source = "🙂\r\n中\t x\ny\r";
+	assert.equal(normalizePathInputValue(source, false), source);
+	assert.equal(normalizePathInputValue(source, true), "🙂中\t xy");
+	assert.deepEqual(normalizePathEdit({ value: source, selection: { anchor: source.length, focus: 4 } }, true), {
+		value: "🙂中\t xy", selection: { anchor: 7, focus: 2 },
+	});
+});
+
+test("single-line mode exposes native input accessibility and horizontal, nonwrapping layout", () => {
+	const html = renderToStaticMarkup(<PathInput value="" onValueChange={() => {}} singleLine className="h-8" />);
+	assert.match(html, /aria-multiline="false"/);
+	assert.match(html, /whitespace-pre /);
+	assert.match(html, /overflow-x-auto/);
+	assert.match(html, /overflow-y-hidden/);
+	assert.doesNotMatch(html, /whitespace-pre-wrap/);
+	assert.match(html, /h-8/);
+});
+
+test("single-line initial/external assignment sanitizes silently; native edits and paste emit sanitized values", async () => {
+	const f = await fixture("one\r\ntwo\n", true);
+	assert.equal(readPathInput(f.root), "onetwo");
+	assert.deepEqual(f.writes, []);
+	await f.external("hello\r\nworld");
+	assert.equal(readPathInput(f.root), "helloworld");
+	assert.deepEqual(f.writes, []);
+	f.select(10);
+	await f.nativeText("ab\r\nc");
+	assert.equal(f.value, "abc");
+	assert.equal(readPathInput(f.root), "abc");
+	assert.equal(pathInputOffset(f.root, f.selection.focusNode!, f.selection.focusOffset), 3);
+	await f.event("paste", { clipboardData: { getData: () => "x\r\n y\n" } });
+	assert.equal(f.value, "abcx y");
+	assert.deepEqual(f.writes, ["abc", "abcx y"]);
+});
+
+test("single-line Enter reaches its consumer but cannot insert a newline", async () => {
+	const f = await fixture("answer", true);
+	f.select(6);
+	await f.event("keydown", { key: "Enter", shiftKey: true });
+	assert.equal(f.keys, 1);
+	const paragraph = await f.event("beforeinput", { inputType: "insertParagraph" });
+	const lineBreak = await f.event("beforeinput", { inputType: "insertLineBreak" });
+	assert.equal(paragraph.defaultPrevented, true);
+	assert.equal(lineBreak.defaultPrevented, true);
+	assert.equal(f.value, "answer");
+	assert.deepEqual(f.writes, []);
+	await f.event(INSERT_FILE_PATHS_EVENT, { detail: ["/course/notes.pdf"] });
+	assert.equal(f.value, "answer `/course/notes.pdf`");
+});
+
+test("single-line IME sanitizes after completion, and queued external assignments do not synthesize changes", async () => {
+	const f = await fixture("a", true);
+	f.select(1);
+	await f.event("compositionstart");
+	f.root.replaceChildren(f.doc.createTextNode("a中\r\n文"));
+	f.select(5);
+	await f.event("input", { isComposing: true });
+	assert.deepEqual(f.writes, []);
+	await f.event("compositionend");
+	assert.equal(f.value, "a中文");
+	assert.equal(readPathInput(f.root), "a中文");
+	await f.event("compositionstart");
+	await f.external("external\r\nvalue");
+	assert.equal(readPathInput(f.root), "a中文", "assignment waits for native composition to finish");
+	await f.event("compositionend");
+	assert.equal(readPathInput(f.root), "externalvalue");
+	assert.deepEqual(f.writes, ["a中文"]);
+});

tests/render-cards.test.tsx

@@ -96,7 +96,7 @@ describe("question submission draft restoration", () => {
 
 	it("restores an ask's custom answer and a free-text answer", () => {
 		const custom = renderToStaticMarkup(<QuestionDock toolName="ask_user_question" toolCallId="ask1" input={{ question: "Fixture?", options: [{ label: "Listed answer" }, { label: "Another answer" }], multiSelect: true }} expanded onExpand={() => {}} onSubmit={() => {}} initialDraft={draft} />);
-		assert.ok(custom.includes('value="preserved custom answer"'));
+		assert.match(custom, /role="textbox"[^>]*aria-multiline="false"[^>]*>preserved custom answer<\/div>/);
 		assert.match(custom, /aria-checked="true" data-testid="other-option"/);
 		const text = renderToStaticMarkup(<QuestionDock toolName="ask_user_question" toolCallId="ask2" input={{ question: "Fixture?" }} expanded onExpand={() => {}} onSubmit={() => {}} initialDraft={draft} />);
 		assert.ok(text.includes("preserved free-text answer"));

tests/render-new-session.test.tsx

@@ -100,7 +100,7 @@ describe("DraftShell — the sessionless surface", () => {
 		const html = renderToStaticMarkup(<DraftShell busy={false} text="keep all my text" onChange={() => {}} onSend={() => {}} startError />);
 		assert.ok(html.includes('role="alert"'));
 		assert.ok(html.includes(OPENING_PROMPT_FAILURE));
-		assert.match(html, /<textarea[^>]*>keep all my text<\/textarea>/);
+		assert.match(html, /<div[^>]*role="textbox"[^>]*contentEditable="true"[^>]*>keep all my text<\/div>/);
 	});
 	it("renders the composer blob, the stats bar, and the fresh-chat empty state", () => {
 		const html = renderToStaticMarkup(

tests/session-find.test.tsx

@@ -81,13 +81,14 @@ describe("sessionFindRanges — the displayed-text DOM seam", () => {
 		assert.ok((ranges[0]!.startContainer as Text).data.includes("session"));
 	});
 
-	it("hidden subtrees never match: hidden attr, menus, katex MathML duplicate, textareas (display:none is browser-verified)", () => {
+	it("hidden subtrees never match: hidden attr, menus, katex MathML duplicate, draft editors (display:none is browser-verified)", () => {
 		mount(`<div data-session-find-root="">
 			<p>needle visible</p>
 			<p hidden>needle hidden-attr</p>
 			<div data-lh-menu><p>needle menu</p></div>
 			<span class="katex-mathml">needle mathml</span>
 			<textarea>needle draft</textarea>
+			<div contenteditable="true" data-file-path-input>needle path draft <span contenteditable="false">notes.pdf</span></div>
 		</div>`);
 		const ranges = sessionFindRanges(document.body as unknown as HTMLElement, "needle");
 		assert.equal(ranges.length, 1);