fix(core): add step-complete contract guard for [email protected]

The backend's AgentEvent union now includes TurnStepCompleteEvent
(wire/transport-contract 0.3.0). Add: no-op case in foldEvent
(transcript reducer ignores timing metadata), exhaustiveness case
in assertAgentEventExhaustive, and a step-complete sample in the
conformance test (now 12 variants).

3 files changed, 18 insertions, 2 deletions

diff --git a/src/core/chunks/reducer.ts b/src/core/chunks/reducer.ts
index 1dcfa39..54b1922 100644
--- a/src/core/chunks/reducer.ts
+++ b/src/core/chunks/reducer.ts
@@ -148,6 +148,10 @@ export function foldEvent(state: TranscriptState, event: AgentEvent): Transcript
 		case "usage":
 			return { ...state, latestUsage: event.usage };
 
+		case "step-complete":
+			// Timing metadata — no content chunk; handled by the telemetry reducer.
+			return state;
+
 		case "done": {
 			const provisional = flushAccumulating(state.provisional, state.accumulating);
 			return {
diff --git a/src/core/wire/conformance.test.ts b/src/core/wire/conformance.test.ts
index 50b7f35..690ba4e 100644
--- a/src/core/wire/conformance.test.ts
+++ b/src/core/wire/conformance.test.ts
@@ -62,6 +62,15 @@ describe("classifies every AgentEvent type", () => {
 			turnId: "t1",
 			usage: { inputTokens: 10, outputTokens: 20 },
 		},
+		{
+			type: "step-complete",
+			conversationId: "c1",
+			turnId: "t1",
+			stepId: "t1#0" as StepId,
+			ttftMs: 300,
+			decodeMs: 700,
+			genTotalMs: 1000,
+		},
 		{ type: "error", conversationId: "c1", turnId: "t1", message: "oops" },
 		{ type: "done", conversationId: "c1", turnId: "t1", reason: "complete" },
 		{ type: "turn-sealed", conversationId: "c1", turnId: "t1" },
@@ -78,14 +87,15 @@ describe("classifies every AgentEvent type", () => {
 			"tool-result",
 			"tool-output",
 			"usage",
+			"step-complete",
 			"error",
 			"done",
 			"turn-sealed",
 		]);
 	});
 
-	it("covers all 11 AgentEvent variants", () => {
-		expect(samples).toHaveLength(11);
+	it("covers all 12 AgentEvent variants", () => {
+		expect(samples).toHaveLength(12);
 	});
 });
 
diff --git a/src/core/wire/conformance.ts b/src/core/wire/conformance.ts
index 5d75a60..d89772e 100644
--- a/src/core/wire/conformance.ts
+++ b/src/core/wire/conformance.ts
@@ -30,6 +30,8 @@ export function assertAgentEventExhaustive(event: AgentEvent): string {
 			return "done";
 		case "turn-sealed":
 			return "turn-sealed";
+		case "step-complete":
+			return "step-complete";
 		default:
 			return event satisfies never;
 	}