browse/src/sse-helpers.ts owns the SSE cleanup invariant:
cleanup runs on abort, enqueue failure, AND heartbeat failure,
exactly once, regardless of which edge fires first.
Pre-helper, /activity/stream and /inspector/events ran cleanup only on
the req.signal.abort edge. If the underlying TCP died without firing
abort (Chromium MV3 service-worker suspend, intermediate proxy
half-close), the subscriber closure stayed in the Set capturing the
ReadableStreamDefaultController plus any payloads queued behind it. Over
a multi-day sidebar session this compounded into multi-MB of retained
controllers per dead connection.
Caller surface: initialReplay (optional, for gap replay or state
snapshots), subscribe (live-event source), liveEventName (SSE event
name for live wrap), heartbeatMs. send() helper handles JSON encoding
with sanitizeReplacer + lone-surrogate stripping.
Unit tests pin all three cleanup edges + idempotency + replay ordering
+ surrogate sanitization. Endpoint refactors land in the next commit.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Garry Tan