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.

components/artifacts/steer-card.tsx

@@ -27,13 +27,14 @@ import { VisualOutputCard } from "@/components/artifacts/visual-card";
 export function SubagentSteerCard({ message }: { message: TeacherUIMessage }) {
 	const artifactPart = message.parts.find((p) => p.type === "data-subagent-artifact");
 	const data = artifactPart?.data as SubagentArtifactData | undefined;
-	// The abort steer (2026-09 dock semantics): no artifact part, only the
-	// metadata marker — a quiet chip, mirroring the complete-badge idiom.
+	// The abort steer (2026-09 dock semantics): its message-type part is
+	// data-subagent-aborted (the custom-message scheme — the part, not
+	// metadata, is the marker) — a quiet chip, mirroring the complete-badge.
 	if (!data) {
-		const meta = (
-				message.metadata as { subagentResult?: { aborted?: boolean; kind?: string } } | undefined
-			)?.subagentResult;
-		if (meta?.aborted) return <AbortedBadge kind={meta.kind ?? "job"} />;
+		const aborted = message.parts.find((p) => p.type === "data-subagent-aborted") as
+			| { data?: { kind?: string } }
+			| undefined;
+		if (aborted?.data) return <AbortedBadge kind={aborted.data.kind ?? "job"} />;
 		return (
 				<div className="rounded-xl border bg-card p-4 text-sm text-muted-foreground">
 				A sub-agent finished, but its result could not be displayed.