#12240: fix: suppress heartbeat agent events from webchat broadcast

## Summary - Apply `shouldSuppressHeartbeatBroadcast` check to the agent event broadcast path in `server-chat.ts` - Chat delta/final messages already filter heartbeat runs, but agent lifecycle/stream events were broadcast unconditionally - This caused webchat to display the full heartbeat execution trace (system prompt, tool calls, HEARTBEAT_OK) when `showOk` was `false` ## Root Cause In `server-chat.ts`, the agent event handler at line 364 broadcasts all non-tool agent events without checking the heartbeat suppression flag: ```typescript // Before (line 364): } else { broadcast("agent", agentPayload); } ``` Meanwhile, `emitChatDelta` (line 250) and `emitChatFinal` (line 281) both gate on `shouldSuppressHeartbeatBroadcast` — the agent event path was simply missed. ## Fix ```typescript // After: } else if (!shouldSuppressHeartbeatBroadcast(evt.runId)) { broadcast("agent", agentPayload); } ``` This matches the existing pattern used for chat messages and ensures heartbeat agent events (lifecycle phases, tool invocations) are not pushed to webchat clients when `showOk` is disabled. ## Test plan - [x] `server-chat.agent-events.test.ts` — 5 tests pass - [x] `server-chat-registry.test.ts` — 10 tests pass - [x] `heartbeat-runner.returns-default-unset.test.ts` — 23 tests pass Closes #12186 <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates `src/gateway/server-chat.ts` to apply the existing heartbeat visibility suppression (`shouldSuppressHeartbeatBroadcast`) to the agent-event broadcast path. Previously, only chat delta/final messages were gated, while non-tool agent lifecycle/stream events were broadcast unconditionally to webchat clients. With this change, heartbeat runs no longer leak their agent event traces to webchat when `showOk` is disabled, aligning agent-event behavior with the already-suppressed chat message path. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - Change is a single-branch conditional that reuses an existing suppression function already applied to chat delta/final broadcasts. No new data shapes or side effects were introduced; it only prevents certain agent events from being broadcast to webchat clients when configured to suppress heartbeat OK traces. - src/gateway/server-chat.ts <!-- greptile_other_comments_section --> <!-- /greptile_comment -->