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/runner.ts

@@ -1,4 +1,4 @@
-import { isToolUIPart, type UIMessage } from "ai";
+import { isToolUIPart } from "ai";
 import type { PiEngine } from "../models.ts";
 import type { SearchProvider } from "../../core/search.ts";
 import {
@@ -14,7 +14,7 @@ import {
 	type PdfToolInput,
 	type ResearchResult,
 	type ResearchToolInput,
-	type SubagentSteerMessage,
+	type SteerMessage,
 	type UsageStepLike,
 	type VisualResult,
 	type VisualToolInput,
@@ -23,6 +23,8 @@ import { registerJobAbort, unregisterJobAbort } from "./aborts.ts";
 import type { ModelRole } from "../../../config.ts";
 import { ROLE_SLOT, modelsNotConfigured, type ModelSlotName, type ProviderKeyMissing } from "../../core/settings.ts";
 import type { ChatStore, JobStore } from "../../core/ports.ts";
+import { projectNative } from "../../core/projection.ts";
+import type { UIMessage } from "ai";
 import { runDemoBuilder } from "./demo-builder.ts";
 import { runPdfReaderAgent } from "./pdf-reader.ts";
 import { runResearcherAgent } from "./researcher.ts";
@@ -69,7 +71,7 @@ export interface JobRunnerDeps {
 	 * steer is delivered (the wake turn completed and the job status
 	 * flipped); rejects when delivery fails unrecoverably.
 	 */
-	deliver: (steer: SubagentSteerMessage) => Promise<void>;
+	deliver: (steer: SteerMessage) => Promise<void>;
 	/** Settings-resolved engine per role (model slots wave, 2026-09-20):
 	 *  the role-override → slot chain, read FRESH per job (the server
 	 *  wiring passes effectiveSettings-based resolution). Test overrides
@@ -274,7 +276,11 @@ export function createJobRunner(deps: JobRunnerDeps): JobRunner {
 		if (input) return input;
 		const chat = chatStore.getChat(job.chatId);
 		if (!chat) return undefined;
-		return (findToolPart(chat.messages, job.toolCallId)?.input ?? undefined) as JobToolInput | undefined;
+		// Wave B: the record is native history — the transcript scan reads
+		// through the projection (same shape the old record held).
+		return (findToolPart(projectNative(chat.messages), job.toolCallId)?.input ?? undefined) as
+			| JobToolInput
+			| undefined;
 	}
 
 	// ─── shared plumbing ────────────────────────────────────────────────────