session kind: ChatRecord.kind teach|practice (absent = teach)

Practice sessions (owner, 2026-10-04): the marker rides the record and
the normalized summary (absent field reads as teach — pre-practice
records never migrate); POST /api/chats accepts {kind: 'practice'}.
The agent branch, tools, and UI land in the following slices.

app/api/chats/route.ts

@@ -17,9 +17,12 @@ export async function GET() {
 }
 
 export async function POST(req: Request) {
-	const body = (await req.json().catch(() => ({}))) as { title?: unknown };
+	const body = (await req.json().catch(() => ({}))) as { title?: unknown; kind?: unknown };
 	const title = typeof body.title === "string" ? body.title : "";
-	const chat = createChat(titleFromPrompt(title || "Untitled session"));
+	// Practice sessions (owner, 2026-10-04): kind "practice" marks the
+	// record — the practice agent + its tools from turn 1, no extraction.
+	const kind = body.kind === "practice" ? ("practice" as const) : undefined;
+	const chat = createChat(titleFromPrompt(title || "Untitled session"), kind);
 	// PER-SESSION MODELS (owner, 2026-09-28): a session owns its model +
 	// thinking level from birth — stamped verbatim from the STRONG slot,
 	// the new-session default. From here the strong slot never reaches

src/core/contracts/chat.ts

@@ -21,12 +21,20 @@ import type { EmissionStats } from "./graph.ts";
  * is the client's own grouping fold (core/view.ts, Wave D) — a pending quiz
  * is an unanswered question tool call, which is exactly what makes
  * resume-mid-question free. */
+/** The session's kind (practice sessions, owner 2026-10-04): "teach" is
+ *  the default and ABSENT on pre-practice records (no migration — absence
+ *  reads as teach); "practice" marks an adaptive-practice session — the
+ *  practice agent, its two tools, no extraction, no graph writes. */
+export type ChatKind = "teach" | "practice";
+
 export interface ChatRecord {
 	id: string;
 	title: string;
 	createdAt: string;
 	updatedAt: string;
 	messages: LhMessage[];
+	/** The session's kind — absent = teach (pre-practice records). */
+	kind?: ChatKind;
 	/** The session's plan tree (vision §2) — written by plan tools via saveTree. */
 	tree?: PlanTree;
 	/** Append-only usage log (observability, 2026-09): one entry per model
@@ -202,6 +210,8 @@ export interface ChatSummary {
 	title: string;
 	createdAt: string;
 	updatedAt: string;
+	/** Normalized kind (absent record field reads as teach). */
+	kind: ChatKind;
 	messageCount: number;
 	/** The session's current phase, derived from the stored plan tree. */
 	phase: Phase3;

src/core/ports.ts

@@ -32,7 +32,9 @@ import type { UserSettings } from "./settings.ts";
 
 export interface ChatStore {
 	/** Create a session record (persisted immediately). */
-	createChat(title: string): ChatRecord;
+	/** Create a session record; kind "practice" marks a practice session
+	 *  (absent = teach, the default). */
+	createChat(title: string, kind?: "practice"): ChatRecord;
 	/** The full record, or null if unknown id / corrupt file. */
 	getChat(id: string): ChatRecord | null;
 	/** All sessions, newest activity first (the sidebar's list view). */

src/store/chats.ts

@@ -31,7 +31,7 @@ function chatFile(id: string): string {
  *  phase, busy, pendingQuestion) is already announced by turn-started /
  *  turn-settled, which the sidebar refetches on. Silence here is law,
  *  not oversight. */
-function createChat(title: string): ChatRecord {
+function createChat(title: string, kind?: "practice"): ChatRecord {
 	const now = new Date().toISOString();
 	const record: ChatRecord = {
 		id: `chat_${Date.now().toString(36)}_${crypto.randomUUID().slice(0, 8)}`,
@@ -39,6 +39,9 @@ function createChat(title: string): ChatRecord {
 		createdAt: now,
 		updatedAt: now,
 		messages: [],
+		// Practice sessions carry the marker; teach stays ABSENT (absence
+		// reads as teach — pre-practice records never migrate).
+		...(kind === "practice" ? { kind: "practice" as const } : {}),
 	};
 	fs.mkdirSync(PATHS.chats, { recursive: true });
 	fs.writeFileSync(chatFile(record.id), JSON.stringify(record, null, "\t"), "utf-8");
@@ -73,6 +76,8 @@ function listChats(): ChatSummary[] {
 						// summaries; usage aggregates ride the full record, the picker
 						// never needs them).
 						...summary,
+						// Normalized kind: absent record field reads as teach.
+						kind: summary.kind ?? "teach",
 						messageCount: messages.length,
 						// Record-derived status for the session picker: phase from the
 						// transcript's explicit events (probe_done concluded / verdict

tests/chat-kind.test.ts

@@ -0,0 +1,46 @@
+/**
+ * SESSION-KIND PINS (practice sessions, owner 2026-10-04): ChatRecord.kind
+ * is ABSENT-BY-DEFAULT — absence reads as teach, so pre-practice records
+ * never migrate; "practice" marks an adaptive-practice session (the
+ * practice agent + its two tools from turn 1, no extraction, no graph
+ * writes). The store normalizes at the summary projection; createChat
+ * stamps the marker only for practice. Runs under an isolated LH_DATA_DIR
+ * (the chat-birth-stamp discipline: the seam is set before any
+ * config-loading import, so every app-module import is dynamic).
+ */
+
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { after, describe, it } from "node:test";
+
+// ── the seam, BEFORE any config-loading import ──────────────────────────────
+const TMP_DATA = fs.mkdtempSync(path.join(os.tmpdir(), "lh-chat-kind-"));
+process.env.LH_DATA_DIR = TMP_DATA;
+
+const { chatStore } = await import("../src/store/chats.ts");
+
+after(() => {
+	fs.rmSync(TMP_DATA, { recursive: true, force: true });
+});
+
+describe("session kind (practice sessions, 2026-10-04)", () => {
+	it("createChat default carries NO kind field — absence reads as teach", () => {
+		const chat = chatStore.createChat("plain session");
+		assert.equal("kind" in chat, false, "teach records carry no kind marker");
+	});
+
+	it("createChat(kind: 'practice') stamps the marker on record + list", () => {
+		const chat = chatStore.createChat("practice session", "practice");
+		assert.equal(chat.kind, "practice");
+		const listed = chatStore.listChats().find((c) => c.id === chat.id);
+		assert.equal(listed?.kind, "practice");
+	});
+
+	it("the summary projection NORMALIZES: absent record field reads as teach", () => {
+		const chat = chatStore.createChat("another plain one");
+		const listed = chatStore.listChats().find((c) => c.id === chat.id);
+		assert.equal(listed?.kind, "teach");
+	});
+});

tests/render-sidebar.test.tsx

@@ -21,6 +21,7 @@ function item(overrides: Partial<ChatListItem>): ChatListItem {
 	return {
 		id: "c1",
 		title: "Test session",
+		kind: "teach",
 		createdAt: "2026-01-01T00:00:00.000Z",
 		updatedAt: "2026-01-02T00:00:00.000Z",
 		messageCount: 4,