Wave D: native AgentEvent wire + client session rewrite (SDK purged)

Server: ui-stream.ts is verbatim pi AgentEvent passthrough (SSE data
lines + [DONE]); only app-level events are the loop-level error and
turn-settled terminal; onError carries raw provider text (owner ruling).

Client: useChat + the AI-SDK transport replaced by components/session-core.ts
(SessionModel: 409 identity-retry, optimistic c_ appends, absorbed()
adoption, needsContinuation, shared consume for POST + reattach) and the
session.ts hook; the golden-master grouping canon moved client-side into
core/view.ts (projectView); scanners read the native record (phaseAt3Lh,
danglingQuestionOf, graph toolParts, plan-blocks, runner, extraction).

Coverage: the native message is the unit (fork 3) with the call+result
inseparability bond rule; view-line-less messages (markers, error
results) are invisible to coverage and never checkpointed.

Deletes: chat-transport, projection, ui-message, their tests (ported to
tests/session-core.test.ts), and the ai + @ai-sdk/react dependencies —
the Vercel SDK is fully out of the tree. Wire pins in chat-flow rewritten
onto the AgentEvent dialect (eventsOf parser).

Gates: tsc clean, 994/994 tests, eslint clean, build green; live smoke
on PORT=3004 (verbatim wire → native record).

src/server/chats.ts

@@ -1,9 +1,7 @@
 import { abortExtraction, extractionStatuses } from "../agent/subagents/extraction.ts";
 import { coverageOf } from "../core/coverage.ts";
-import { projectNative } from "../core/projection.ts";
 import { deleteChatTraces, type ChatDeleteMode, type ChatDeletionStats } from "../core/graph-deletion.ts";
 import { titleFromPrompt } from "../core/contracts.ts";
-import type { UIMessage } from "ai";
 import { graphRevision } from "./graph.ts";
 import { stores } from "./stores.ts";
 import { isTurnRunning } from "./turn-liveness.ts";
@@ -144,7 +142,7 @@ export function sessionCoverage(chatId: string): SessionCoverage | null {
 	const entries = stores.graphStore.readCoverage();
 	// Wave B: the record is native history — coverage reads through the
 	// projection (same view the extraction pipeline folds).
-	const cov = coverageOf(projectNative(record.messages), entries, chatId);
+	const cov = coverageOf(record.messages, entries, chatId);
 	let lastFoldedAt: string | null = null;
 	for (const entry of entries) {
 		if (entry.chatId !== chatId) continue;