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).

components/artifacts/steer-card.tsx

@@ -1,7 +1,8 @@
 "use client";
 
 import { CheckIcon, CircleX } from "lucide-react";
-import type { PdfResult, ResearchResult, SubagentArtifactData, TeacherUIMessage } from "@/src/core";
+import type { PdfResult, ResearchResult, SubagentArtifactData } from "@/src/core";
+import type { LhViewMessage } from "@/src/core";
 import { isSubagentFailure } from "@/src/core";
 import { DemoOutputCard } from "@/components/artifacts/demo-card";
 import { PdfBriefCard, ResearchBriefCard } from "@/components/artifacts/job-card";
@@ -24,7 +25,7 @@ import { VisualOutputCard } from "@/components/artifacts/visual-card";
  *     The sub-agent's verification notes are model-facing glue and do NOT
  *     render; only a failure note does.
  */
-export function SubagentSteerCard({ message }: { message: TeacherUIMessage }) {
+export function SubagentSteerCard({ message }: { message: LhViewMessage }) {
 	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): its message-type part is