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/render-practice.test.tsx

@@ -87,6 +87,8 @@ describe("PracticeDialogBody — creation (cluster picker)", () => {
 	const base = {
 		params: { ...DEFAULT_PRACTICE_PARAMS },
 		onParam: () => {},
+		note: "",
+		onNote: () => {},
 		clusters: clusters(),
 		selectedKey: null,
 		onSelect: () => {},
@@ -126,6 +128,17 @@ describe("PracticeDialogBody — creation (cluster picker)", () => {
 		assert.match(moved, /param-presentation-application[^]*border-primary/, "application segment active");
 	});
 
+	it("the learner's note: optional textarea under the params, carries text, capped client-side", () => {
+		const html = renderToStaticMarkup(<PracticeDialogBody {...base} note="lean toward pricing applications" />);
+		assert.ok(html.includes('data-testid="practice-note"'));
+		assert.ok(html.includes("Anything else? (optional)"), "the label");
+		assert.ok(html.includes("lean toward pricing applications"), "controlled value renders");
+		assert.match(html, /maxlength="2000"/i, "client-side cap mirrors the API law");
+		// Empty default: present but empty — optional in every sense.
+		const bare = renderToStaticMarkup(<PracticeDialogBody {...base} />);
+		assert.match(bare, /data-testid="practice-note"[^>]*><\/textarea>/, "no value when unset");
+	});
+
 	it("cluster picker: label + proposition-count rows, notes kind marked, Create gated until picked", () => {
 		const html = renderToStaticMarkup(<PracticeDialogBody {...base} />);
 		assert.ok(html.includes('data-testid="practice-dialog-clusters"'));