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.

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). */