feat: probe/teach agent split — explicit phase markers, position-only plan map

Diagnosis (2026-09-11 user testing, minimal-effort GLM): sessions stuck on
'plan' forever. Two causes: (1) the three-phase view read the stored tree's
currentNodeId, which nothing ever writes post author-once (2026-09-03) — a
structural dead seam; (2) the teacher stochastically left quiz.nodeId
untagged, and done-by-quiz-result semantics would have falsely completed
nodes anyway.

The redesign (docs/probe-teach-split.md) abolishes derived occupancy in
favor of explicit events:

- Two agents over one transcript: createProberAgent (quiz without a
  nodeId field, ask, probe_done) and createTeacherAgent (full toolset,
  plan_init onward). The chat-handler construction branch keys on a
  probe_done part in the transcript. MODELS.prober added.
- probe_done: server-side seam tool — carries the learner assessment
  (strands + free-form edge read), refuses while a question is open or
  the probe is already concluded, and queues a handoff steer through the
  generalized wake pipeline (steers now dedupe by id, not jobId; job
  finalization only for job steers). The teacher auto-wakes and authors
  the plan; the learner sees the assessment via the probe-done card.
- phases: probe ends at a concluded probe_done, plan ends at a
  successful plan_init — strictly sequential, no skipping, no legacy
  compatibility (data wiped at the pivot per doctrine).
- Plan map = position, not completion: derivePlanStatuses reads only
  tagged quiz CALLS (state/outcome feed nothing); current = latest
  tagged node with consecutive duplicates collapsed, visited = earlier
  distinct stays (a revisit stays in both — current wins at render).
  PlanTree is structure-only; currentNodeId/doneNodeIds and the dead
  mutation helpers are gone. No fallback current.
- Prompts split per agent (prompts/prober/, prompts/teacher/ over the
  trimmed shared base); graph-context injection removed entirely
  (shelved, docs/probe-teach-split.md §5); knowledge-graph context no
  longer reaches either agent.
- Plan blocks are full-only snapshots at plan_init (neighborhood
  machinery retired; the persistent DAG window is the future UI wave);
  usage capture unchanged.

Gates: tsc clean, 294/294 tests (phases/plan-tree/plan-blocks/question-
tools rewritten to the new semantics; probe-done + handoff-wake tests
added), lint, build. Live GLM smoke PASS: prober concluded with an honest
assessment, teacher auto-woke, authored a 10-node plan with the block
attached, then tagged checks on slope-instinct → secant derived current/
visited exactly as designed; grading honest both ways (driver off-by-one
proved a wrong answer grades false).

tests/chat-flow.test.ts

@@ -113,7 +113,7 @@ after(() => {
 describe("teacher chat flow (scripted model)", () => {
 	it("quiz tool call persists as a pending part; the answer continues the lesson", async () => {
 		const calls: string[][] = [];
-		const agent = createTeacherAgent(scriptedModel(calls));
+		const agent = createTeacherAgent(undefined, scriptedModel(calls));
 		const chat = chatStore.createChat("Test: solar system");
 		createdChats.push(chat.id);
 
@@ -200,7 +200,7 @@ describe("teacher chat flow (scripted model)", () => {
 		// 'input-streaming', which the stream processor sets from the
 		// tool-input-start chunk. If a transport change ever stopped emitting
 		// it, the indicator would silently die — pin the protocol.
-		const agent = createTeacherAgent(scriptedModel([]));
+		const agent = createTeacherAgent(undefined, scriptedModel([]));
 		const chat = chatStore.createChat("Test: protocol pin");
 		createdChats.push(chat.id);
 		const firstUser = { id: "u1", role: "user", parts: [{ type: "text", text: "quiz me" }] };
@@ -214,7 +214,7 @@ describe("teacher chat flow (scripted model)", () => {
 
 	it("persists even when the stream is aborted (resume keeps partial state)", async () => {
 		const calls: string[][] = [];
-		const agent = createTeacherAgent(scriptedModel(calls));
+		const agent = createTeacherAgent(undefined, scriptedModel(calls));
 		const chat = chatStore.createChat("Test: abort");
 		createdChats.push(chat.id);
 
@@ -283,7 +283,7 @@ describe("teacher chat flow (scripted model)", () => {
 			},
 		});
 
-		const agent = createTeacherAgent(retryModel);
+		const agent = createTeacherAgent(undefined, retryModel);
 		const chat = chatStore.createChat("Test: bad quiz retry");
 		createdChats.push(chat.id);
 		const firstUser = { id: "u1", role: "user", parts: [{ type: "text", text: "quiz me" }] };
@@ -331,7 +331,7 @@ describe("chat store", () => {
 describe("mid-turn navigation (turn liveness + write-ahead)", () => {
 	it("one turn per chat: a concurrent request is 409'd; the next one after finish is accepted", async () => {
 		const calls: string[][] = [];
-		const agent = createTeacherAgent(scriptedModel(calls));
+		const agent = createTeacherAgent(undefined, scriptedModel(calls));
 		const chat = chatStore.createChat("Test: turn guard");
 		createdChats.push(chat.id);
 
@@ -353,7 +353,7 @@ describe("mid-turn navigation (turn liveness + write-ahead)", () => {
 
 	it("write-ahead: the learner's answer is durable BEFORE the turn finishes", async () => {
 		const calls: string[][] = [];
-		const agent = createTeacherAgent(scriptedModel(calls));
+		const agent = createTeacherAgent(undefined, scriptedModel(calls));
 		const chat = chatStore.createChat("Test: write-ahead");
 		createdChats.push(chat.id);
 
@@ -408,14 +408,14 @@ describe("mid-turn navigation (turn liveness + write-ahead)", () => {
 		// A text part with no text: fails UIMessage validation before the stream
 		// exists — the path where no onFinish will ever run.
 		const bad = [{ id: "m1", role: "user", parts: [{ type: "text" }] }];
-		const res = await handleChatRequest(post(chat.id, bad), createTeacherAgent(scriptedModel([])));
+		const res = await handleChatRequest(post(chat.id, bad), createTeacherAgent(undefined, scriptedModel([])));
 		assert.equal(res.status, 500, "turn-start failure is a 500, not a hang");
 		assert.equal(isTurnRunning(chat.id), false, "registry cleared when the stream never started");
 
 		// And the chat is NOT locked: the next (valid) turn is accepted.
 		const ok = await handleChatRequest(
 			post(chat.id, [{ id: "m1", role: "user", parts: [{ type: "text", text: "teach me" }] }]),
-			createTeacherAgent(scriptedModel([])),
+			createTeacherAgent(undefined, scriptedModel([])),
 		);
 		assert.equal(ok.status, 200);
 		await drain(ok);