feat(wire,kernel,session-orchestrator): live turn metrics on the stream

Expose the backend's authoritative token+timing metrics on the live AgentEvent
stream (observability-only -> now also client-facing). All additive/optional.

- [email protected]: new TurnStepCompleteEvent (type:step-complete) with per-step
  ttftMs/decodeMs/genTotalMs; usage += stepId; tool-result += durationMs (exec);
  done += durationMs (turn wall-clock) + usage (turn total). RunTurnInput += now?.
  [email protected] (re-export bump).
- kernel-runtime: when now injected, measures + emits the above (reuses the
  ttft/decode first-token detection); omits timing gracefully without a clock.
- session-orchestrator: adds now? to deps, threads into RunTurnInput; extension
  activate injects () => Date.now().
- transport/cli/host-bin: untouched (verbatim pass-through; additive fields).

FE handoff: frontend-metrics-handoff.md. typecheck clean; 520 vitest + 89 bun;
biome 0/0. Replay/persistence = deferred Pass 2 (documented in tasks.md).

3 files changed, 51 insertions, 0 deletions

diff --git a/packages/session-orchestrator/src/extension.ts b/packages/session-orchestrator/src/extension.ts
index af7d6e0..fbb7c15 100644
--- a/packages/session-orchestrator/src/extension.ts
+++ b/packages/session-orchestrator/src/extension.ts
@@ -38,6 +38,7 @@ export function activate(host: HostAPI): void {
 		},
 		runTurn,
 		logger: host.logger,
+		now: () => Date.now(),
 	});
 
 	host.provideService(sessionOrchestratorHandle, orchestrator);
diff --git a/packages/session-orchestrator/src/orchestrator.test.ts b/packages/session-orchestrator/src/orchestrator.test.ts
index b648d42..3954ffe 100644
--- a/packages/session-orchestrator/src/orchestrator.test.ts
+++ b/packages/session-orchestrator/src/orchestrator.test.ts
@@ -363,6 +363,53 @@ describe("handleMessage model resolution", () => {
 		expect(captured).toHaveLength(2);
 		expect(captured[1]?.cwd).toBeUndefined();
 	});
+
+	it("forwards an injected now into the RunTurnInput passed to runTurn", async () => {
+		const store = createInMemoryStore();
+		const provider: ProviderContract = { id: "p", stream: async function* () {} };
+		const { captured, captureRunTurn } = createCapturingRunTurn();
+		const fakeNow = () => 42;
+
+		const orchestrator = createSessionOrchestrator({
+			conversationStore: store,
+			resolveProvider: () => provider,
+			resolveTools: () => [],
+			runTurn: captureRunTurn,
+			now: fakeNow,
+		});
+
+		await orchestrator.handleMessage({
+			conversationId: "conv-now",
+			text: "hi",
+			onEvent: () => {},
+		});
+
+		expect(captured).toHaveLength(1);
+		expect(captured[0]?.now).toBe(fakeNow);
+		expect(captured[0]?.now?.()).toBe(42);
+	});
+
+	it("omits now from RunTurnInput when deps.now is not provided", async () => {
+		const store = createInMemoryStore();
+		const provider: ProviderContract = { id: "p", stream: async function* () {} };
+		const { captured, captureRunTurn } = createCapturingRunTurn();
+
+		const orchestrator = createSessionOrchestrator({
+			conversationStore: store,
+			resolveProvider: () => provider,
+			resolveTools: () => [],
+			runTurn: captureRunTurn,
+		});
+
+		await orchestrator.handleMessage({
+			conversationId: "conv-no-now",
+			text: "hi",
+			onEvent: () => {},
+		});
+
+		expect(captured).toHaveLength(1);
+		expect(captured[0]?.now).toBeUndefined();
+	});
 });
 
 describe("turn-sealed event", () => {
diff --git a/packages/session-orchestrator/src/orchestrator.ts b/packages/session-orchestrator/src/orchestrator.ts
index 311b620..04f6ad2 100644
--- a/packages/session-orchestrator/src/orchestrator.ts
+++ b/packages/session-orchestrator/src/orchestrator.ts
@@ -39,6 +39,8 @@ export interface SessionOrchestratorDeps {
 	readonly runTurn: (input: RunTurnInput) => Promise<RunTurnResult>;
 	/** Base logger (auto-scoped to this extension); childed per turn for span capture. */
 	readonly logger?: Logger;
+	/** Injected monotonic-ish clock (ms) forwarded to RunTurnInput for timing events. */
+	readonly now?: () => number;
 }
 
 export function createSessionOrchestrator(deps: SessionOrchestratorDeps): SessionOrchestrator {
@@ -86,6 +88,7 @@ export function createSessionOrchestrator(deps: SessionOrchestratorDeps): Sessio
 				...(turnLogger !== undefined ? { logger: turnLogger } : {}),
 				...(signal !== undefined ? { signal } : {}),
 				...(cwd !== undefined ? { cwd } : {}),
+				...(deps.now !== undefined ? { now: deps.now } : {}),
 			};
 
 			const result = await deps.runTurn(opts);