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).

src/core/contracts/probe.ts

@@ -0,0 +1,45 @@
+/**
+ * Probe-phase contracts (the probe→teach split, docs/probe-teach-split.md).
+ *
+ * The prober concludes its phase with `probe_done` — a server-side tool
+ * whose INPUT is the learner assessment (authored by the model, streamed to
+ * the learner live, durable in the transcript by the tool result itself).
+ * The first `probe_done` in the transcript is the probe→planning seam: the
+ * teacher agent is constructed from that point on, and the tool's execute
+ * queues the handoff steer through the wake pipeline so the teacher starts
+ * immediately after the prober's turn ends (auto-wake, user-decided).
+ *
+ * Assessment shape (v1 — refine later): the probe was a binary search per
+ * dependency strand; the assessment formalizes exactly that. A list of the
+ * strands the lesson will depend on, each with a free-form read of where
+ * the learner's edge sits.
+ */
+
+/** One dependency strand the planned lesson will rest on. */
+export interface ProbeStrand {
+	/** Name/description of the strand (e.g. "the derivative as a limit"). */
+	strand: string;
+	/** Free-form: where the learner's edge sits on this strand — floor,
+	 *  ceiling, misconceptions found, what to build from. */
+	assessment: string;
+}
+
+/** The prober's read of the learner, carried by probe_done. */
+export interface ProbeAssessment {
+	strands: ProbeStrand[];
+	/** Optional overall synthesis: the learner's apparent goal and edge. */
+	summary?: string;
+}
+
+/** probe_done tool input (the assessment the prober authors). */
+export interface ProbeDoneInput {
+	assessment: ProbeAssessment;
+}
+
+/** probe_done tool output. */
+export interface ProbeDoneResult {
+	ok: boolean;
+	/** Refusal reason when ok === false (open question, already concluded). */
+	error?: string;
+	assessment?: ProbeAssessment;
+}