test(claude): give the idle-ping test headroom against timer scheduling

Failed on macos-latest while passing everywhere else. The upstream went
silent for 90ms with a 25ms ping interval and the test asserted >=3
pings — a margin of 3.6 intervals. One coalesced timer on a loaded
runner is enough to miss it, and timer scheduling is best-effort by
definition.

Silence goes to 300ms, twelve intervals against the same >=3. The
assertion is untouched: it still proves idle pings flow during upstream
silence, it just no longer depends on the runner delivering timers on
schedule.

Ablated by disabling the ping branch in src/claude/outbound.ts — the
test fails, so the headroom did not hollow it out.

Author: lidge-jun

tests/claude-outbound.test.ts

@@ -341,17 +341,28 @@ describe("claude outbound SSE", () => {
   });
 
   test("idle keepalive pings flow during upstream silence", async () => {
-    // Upstream: created frame, 90ms of silence, then a clean completion.
+    // Upstream: created frame, a stretch of silence, then a clean completion.
+    //
+    // The silence is deliberately many intervals long. At 90ms with a 25ms ping the
+    // margin was 3.6 intervals against a >=3 assertion, so a single coalesced timer on
+    // a loaded runner failed it — which is how this went red on macos-latest while
+    // passing everywhere else. Timer scheduling is best-effort, not exact.
+    //
+    // The assertion below is unchanged. What changed is the headroom: the test still
+    // proves idle pings flow during silence, it just no longer depends on the runner
+    // delivering timers on schedule.
+    const PING_INTERVAL_MS = 25;
+    const SILENCE_MS = 300;
     const encoder = new TextEncoder();
     const upstream = new ReadableStream<Uint8Array>({
       async start(controller) {
         controller.enqueue(encoder.encode(sse("response.created", { response: {} })));
-        await new Promise(r => setTimeout(r, 90));
+        await new Promise(r => setTimeout(r, SILENCE_MS));
         controller.enqueue(encoder.encode(sse("response.completed", { response: { status: "completed", usage: { input_tokens: 1, output_tokens: 1 } } })));
         controller.close();
       },
     });
-    const events = await collectEvents(responsesSseToAnthropicSse(upstream, "m", { pingIntervalMs: 25 }));
+    const events = await collectEvents(responsesSseToAnthropicSse(upstream, "m", { pingIntervalMs: PING_INTERVAL_MS }));
     const pings = events.filter(e => e.name === "ping").length;
     expect(pings).toBeGreaterThanOrEqual(3); // startup ping + >=2 idle pings
     expect(events.at(-1)!.name).toBe("message_stop");