practice: the learner's creation note — optional free-form input carried to partitioner + generators (owner, 2026-09-29)

- dialog: optional 'Anything else?' textarea (typing-only, 2000-char mirror)
- API: body gains note? — trimmed, whitespace-only omitted, hard 400 over 2000
- pipeline: note persisted on the set and threaded to both agent stages
- agents: THE LEARNER'S NOTE prompt block (present only when set) + the
  weighed-never-owed stance pinned in both doctrines
- fix en route: doubled THE PARAMETERS heading in both prompts since slice 3
  (renderParams owns the heading; the literal blocks removed)

tests/practice-service.test.ts

@@ -41,3 +41,29 @@ describe("createPracticeSetResponse — strict named-level params", () => {
 		assert.equal(await statusOf("high"), 400);
 	});
 });
+
+describe("createPracticeSetResponse — the learner's note (owner, 2026-09-29)", () => {
+	const PARAMS = { ladderRung: 2, cueDistance: 1, presentation: "theory" } as const;
+
+	it("non-string note → 400", async () => {
+		const res = await createPracticeSetResponse({ ...NODE_IDS, params: PARAMS, note: 42 });
+		assert.equal(res.status, 400);
+	});
+
+	it("over 2000 characters → 400 (the API is the law; the textarea's maxLength mirrors it)", async () => {
+		const res = await createPracticeSetResponse({ ...NODE_IDS, params: PARAMS, note: "x".repeat(2001) });
+		assert.equal(res.status, 400);
+		const body = (await res.json()) as { error: string };
+		assert.match(body.error, /over 2000 characters/);
+	});
+
+	it("exactly 2000 passes the note check (boundary — the next check, not the note, refuses)", async () => {
+		// Malformed nodeIds AFTER a max-length note: reaching the nodeIds
+		// error proves the note check passed (all checks are rejecting-path;
+		// the pipeline is never reached — this suite's doctrine).
+		const res = await createPracticeSetResponse({ nodeIds: 5, params: PARAMS, note: "x".repeat(2000) });
+		assert.equal(res.status, 400);
+		const body = (await res.json()) as { error: string };
+		assert.match(body.error, /Body must be/);
+	});
+});