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).

tests/stream-activity.test.ts

@@ -7,11 +7,11 @@
  */
 import assert from "node:assert/strict";
 import { describe, it } from "node:test";
-import type { UIMessage } from "ai";
+import type { LhViewMessage } from "../src/core/view.ts";
 import { streamingToolActivity } from "../src/core/pending.ts";
 
-function msg(role: string, parts: unknown[]): UIMessage {
-	return { id: "m1", role, parts } as unknown as UIMessage;
+function msg(role: string, parts: unknown[]): LhViewMessage {
+	return { id: "m1", role, parts } as unknown as LhViewMessage;
 }
 
 function toolPart(tool: string, state: string) {