feat: attach desktop file paths as editable learner chips

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.