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).

1 files changed, 76 insertions, 4 deletions

diff --git a/packages/kernel/src/runtime/events.ts b/packages/kernel/src/runtime/events.ts
index deeb012..300e711 100644
--- a/packages/kernel/src/runtime/events.ts
+++ b/packages/kernel/src/runtime/events.ts
@@ -33,9 +33,10 @@ export function toolResultEvent(
 	toolName: string,
 	content: string,
 	isError: boolean,
+	durationMs?: number,
 ): AgentEvent {
-	return {
-		type: "tool-result",
+	const base = {
+		type: "tool-result" as const,
 		conversationId,
 		turnId,
 		stepId,
@@ -44,6 +45,10 @@ export function toolResultEvent(
 		content,
 		isError,
 	};
+	if (durationMs !== undefined) {
+		return { ...base, durationMs };
+	}
+	return base;
 }
 
 export function toolOutputEvent(
@@ -56,7 +61,15 @@ export function toolOutputEvent(
 	return { type: "tool-output", conversationId, turnId, toolCallId, data, stream };
 }
 
-export function usageEvent(conversationId: string, turnId: string, usage: Usage): AgentEvent {
+export function usageEvent(
+	conversationId: string,
+	turnId: string,
+	usage: Usage,
+	stepId?: StepId,
+): AgentEvent {
+	if (stepId !== undefined) {
+		return { type: "usage", conversationId, turnId, usage, stepId };
+	}
 	return { type: "usage", conversationId, turnId, usage };
 }
 
@@ -64,7 +77,66 @@ export function turnStartEvent(conversationId: string, turnId: string): AgentEve
 	return { type: "turn-start", conversationId, turnId };
 }
 
-export function doneEvent(conversationId: string, turnId: string, reason: string): AgentEvent {
+export function stepCompleteEvent(
+	conversationId: string,
+	turnId: string,
+	stepId: StepId,
+	timing?: { ttftMs?: number; decodeMs?: number; genTotalMs?: number },
+): AgentEvent {
+	if (timing !== undefined) {
+		if (timing.ttftMs !== undefined) {
+			if (timing.decodeMs !== undefined && timing.genTotalMs !== undefined) {
+				return {
+					type: "step-complete",
+					conversationId,
+					turnId,
+					stepId,
+					ttftMs: timing.ttftMs,
+					decodeMs: timing.decodeMs,
+					genTotalMs: timing.genTotalMs,
+				};
+			}
+			if (timing.genTotalMs !== undefined) {
+				return {
+					type: "step-complete",
+					conversationId,
+					turnId,
+					stepId,
+					ttftMs: timing.ttftMs,
+					genTotalMs: timing.genTotalMs,
+				};
+			}
+			return { type: "step-complete", conversationId, turnId, stepId, ttftMs: timing.ttftMs };
+		}
+		if (timing.genTotalMs !== undefined) {
+			return {
+				type: "step-complete",
+				conversationId,
+				turnId,
+				stepId,
+				genTotalMs: timing.genTotalMs,
+			};
+		}
+	}
+	return { type: "step-complete", conversationId, turnId, stepId };
+}
+
+export function doneEvent(
+	conversationId: string,
+	turnId: string,
+	reason: string,
+	durationMs?: number,
+	usage?: Usage,
+): AgentEvent {
+	if (durationMs !== undefined && usage !== undefined) {
+		return { type: "done", conversationId, turnId, reason, durationMs, usage };
+	}
+	if (durationMs !== undefined) {
+		return { type: "done", conversationId, turnId, reason, durationMs };
+	}
+	if (usage !== undefined) {
+		return { type: "done", conversationId, turnId, reason, usage };
+	}
 	return { type: "done", conversationId, turnId, reason };
 }