feat: custom message types for system turns — wake and verdict messages

The custom-message scheme (user-decided 2026-09-12): system-authored
user-role messages are NOT human messages — they carry marker data parts
only, the adapter owns their model-facing wording, and the UI renders
them under control. Nothing fake is ever persisted as human speech.

The inventory (all migrated):
- probe→teacher handoff wake: was a text-bearing user message rendering
  as a fake user bubble; now data-probe-handoff marker-only — the
  adapter flattens it to HANDOFF_TEXT (core/contracts/chat.ts), the UI
  renders a quiet 'Preparing your plan…' system line.
- plan accept/decline: was boilerplate text ('The plan is accepted…',
  'I'd like the plan revised…') masquerading as learner speech — the
  decline wasn't even marked; now data-verdict {accepted, at} on its own
  message, adapter flattens to verdictText(), UI renders the quiet
  verdict marker ('✓ Plan accepted' / '↻ Plan revision requested').
  sendVerdict sends TWO REAL MESSAGES when the learner typed a note
  (the note as a genuine user message, then the verdict) in ONE turn
  via setMessages + sendMessage() — no 409 dance, no double teacher turn.
- sub-agent steers: the abort steer gains its data-subagent-aborted
  marker part; the UI keys steer rendering off PARTS (artifact/aborted),
  not metadata — metadata stays as pump mechanics only.
- record-adapter: systemTextOf() flattens marker-only messages; steers
  keep their text (payload — briefs are content, not boilerplate).

phases.ts: plan→teach advances on data-verdict{accepted:true} only;
learner text alone can never sanction teaching (pinned). data-plan-
accepted retired, no back-compat (user-decided: wiped-data doctrine).

Pinned: record-adapter.test.ts (verdict/handoff flattening, note+verdict
order, steer payload kept, UI-only parts skipped), phases.test.ts
(verdict marker semantics, out-of-order, text-never-fakes), jobs.test.ts
(abort marker part), demos.test.tsx (badge renders off the part, not
metadata).

Live GLM smoke (disposable driver, deleted): probe→conclude→wake→plan→
decline-with-note (revised, still plan)→accept-with-note (teach) — ALL
CHECKS PASS, including marker-only handoff/verdict on the wire and zero
fake human speech in the transcript.

Gates: tsc, lint, build, 335/335.

src/core/ui-message.ts

@@ -1,12 +1,13 @@
 import type { UIMessage } from "ai";
 import type {
 	DemoToolInput,
-	PlanAcceptedData,
+	PlanVerdictData,
 	PlanBlockData,
 	ProbeDoneInput,
 	ProbeDoneResult,
 	ResearchToolInput,
 	SubagentArtifactData,
+	SubagentResultMeta,
 	VisualToolInput,
 } from "./contracts.ts";
 import type { AskToolInput, QuestionAnswerData, QuizToolInput } from "./question-core.ts";
@@ -38,9 +39,15 @@ export type TeacherUIDataParts = {
 	"subagent-artifact": SubagentArtifactData;
 	/** Plan blocks (wave 4): frozen plan snapshots rendered in the chat flow. */
 	"plan-block": PlanBlockData;
-	/** The plan-acceptance marker: the accept button's user message carries
-	 *  it — the plan→teach phase seam (docs/probe-teach-split.md §4). */
-	"plan-accepted": PlanAcceptedData;
+	/** The learner's plan verdict (accept/decline): its own user message,
+	 *  carrying ONLY this part — the plan→teach phase seam (docs/probe-
+	 *  teach-split.md §4, the custom-message scheme 2026-09-12). */
+	verdict: PlanVerdictData;
+	/** The probe→teach handoff wake: the wake pipeline's steer message,
+	 *  carrying ONLY this part (the model-facing text lives in the adapter). */
+	"probe-handoff": { chatId: string };
+	/** The abort steer's message-type marker (the abort badge renders off it). */
+	"subagent-aborted": SubagentResultMeta & { aborted: true };
 };
 
 export type TeacherUIMessage = UIMessage<unknown, TeacherUIDataParts, TeacherUITools>;