Wave B: the native message record — input events, projection, adapter death

The chat record is now pi-native agent history (LhMessage[]), the AI SDK's
UIMessage transcript contract is gone from the server, and every client turn
arrives as ONE explicit input event.

Core (new):
- src/core/native-messages.ts — the LhMessage taxonomy (user/assistant/
  toolResult + lhMarker customs: verdict, probe-handoff, subagent-steer,
  subagent-abort, plan-block), constructors, and toLlmMessages — the single
  model-facing seam (convertToLlm): strips ids, flattens markers to user
  text, drops UI-only plan-blocks, synthesizes INTERRUPTED results for
  dangling aborted calls, never throws.
- src/core/projection.ts — projectNative: the one-way native → UIMessage
  projection (consecutive assistant+toolResult runs group into one
  assistant view message; toolResults attach backward by toolCallId;
  markers project to data parts; plan-blocks splice after the last
  successful plan_init). Every existing consumer reads through it.
- src/core/input-events.ts — the ChatInput union (text/answer/verdict/
  continue), parseChatInput validation, and inputAppends (answer targets
  the dangling question call or 400s; verdict = optional note user
  message + native verdict marker).

Server:
- chat-handler.ts — the turn root takes {chatId, input}; write-ahead
  persists input appends + claimed steers before the turn; claimSteers
  coalesces the whole queue with the handler's steerDelivered filter as
  the dedupe seam; teacher-vs-prober branch on hasProbeDone.
- turn-service.ts — persistTurn stamps ids, drops clean question
  placeholder toolResults (the record ends at the unanswered call),
  emits plan-block markers idempotently (plan-blocks.ts rewrite), and
  persists abort partials.
- ui-stream.ts — PiTurnSpec takes the native base; the wire dialect is
  unchanged. jobs.ts steers are native markers (steer_<jobId> dedup ids);
  waitForIdle reads danglingQuestionOf. teacher-agent.ts wires
  convertToLlm: toLlmMessages. record-adapter.ts DELETED wholesale.
- GET /api/chats/[id] serves messages: projectNative(record.messages).

Client:
- chat-transport.ts — the 409 retry is IDENTITY (re-POST the same event
  body after the turn settles — the event was never persisted
  pre-acceptance; the merge logic is gone). The transport consumes the
  stashed input event via prepareSendMessagesRequest and throws loudly on
  a missing stash.
- chat.tsx — every send call site stashes exactly one ChatInput event
  (text, answer, verdict, continue) before invoking the SDK send.

Tests: full native migration (chat-flow rewritten to input events and
native record pins; jobs/extraction/demos/graph/usage/plan-blocks/
probe-done/reattach-transport converted; record-adapter.test.ts deleted;
chat-transport tests pin the identity retry). 982/982, typecheck, lint,
build all green.

src/agent/subagents/extraction.ts

@@ -28,6 +28,7 @@ import { getGraph, mergeFindings, type EmissionStats, type GraphDeps } from "../
 import type { GraphStore } from "../../core/ports.ts";
 import { settleGraphLayout } from "../../core/layout-settle.ts";
 import { batchRuns, batchTag, coverageOf, messageViewLines } from "../../core/coverage.ts";
+import { projectNative } from "../../core/projection.ts";
 
 /**
  * The extraction pipeline (vision §1 construction, 2026-09-02 redesign) — the
@@ -92,10 +93,12 @@ import { batchRuns, batchTag, coverageOf, messageViewLines } from "../../core/co
 export function transcriptView(record: ChatRecord): string {
 	// The shared seam (core/coverage.ts messageViewLines): the LLM's prompt
 	// view and the coverage fingerprint use ONE line builder, so "covered"
-	// means — exactly — what the extractor saw.
+	// means — exactly — what the extractor saw. Wave B: the record is native
+	// history — the extraction view reads through the one-way projection.
 	const lines = [`SESSION: ${record.title}`];
-	record.messages.forEach((message, index) => {
-		lines.push(...messageViewLines(message as UIMessage, (message as UIMessage).id || `m${index}`));
+	const projected = projectNative(record.messages);
+	projected.forEach((message, index) => {
+		lines.push(...messageViewLines(message, message.id || `m${index}`));
 	});
 	return lines.join("\n");
 }
@@ -868,7 +871,8 @@ export function createExtractionPipeline(deps: ExtractionPipelineDeps): Extracti
 			// engines AND their providers' keys; a refusal lands BEFORE any
 			// stage runs (typed — the trigger skips, routes surface 503).
 			refuseIfStagesUnready();
-			const covered = coverageOf(record.messages as UIMessage[], graphStore.readCoverage(), chatId);
+			const projected = projectNative(record.messages);
+			const covered = coverageOf(projected, graphStore.readCoverage(), chatId);
 			if (covered.uncovered.length === 0) {
 				console.info(`[extraction ${chatId}] nothing uncovered — no-op`);
 				return { nodes: 0, edges: 0, events: 0 };
@@ -883,11 +887,11 @@ export function createExtractionPipeline(deps: ExtractionPipelineDeps): Extracti
 				// The batch's prompt view: SESSION header + the batch's lines,
 				// same provenance [id] tags the fingerprints used (coverage
 				// and prompt share ONE line builder — core/coverage.ts).
-				const mids = record.messages.map((m, i) => ((m as UIMessage).id || `m${i}`) as string);
+				const mids = projected.map((m, i) => (m.id || `m${i}`) as string);
 				const view = [
 					`SESSION: ${record.title}`,
 					...batch.flatMap((slot) => {
-						const idx = record.messages.indexOf(slot.message);
+						const idx = projected.indexOf(slot.message);
 						return messageViewLines(slot.message, mids[idx] ?? slot.message.id);
 					}),
 				].join("\n");