fix(ws): surface inbound frame errors instead of silently dropping events (fixes #201)

[Xuxchloris]

Fixes #201

Problem

Under load, the WSClient silently loses events that Feishu delivered and ACKed at the transport level: the [ws] receive message debug line never appears for the dropped event, no error is logged, no disconnect fires, and the handler is never invoked.

The receive path is an async 'message' listener with no error handling:

wsInstance?.on('message', async (buffer) => {
  const data = protoBuf.decode(buffer);       // throws on malformed frames
  ...
  await this.handleControlData(data);          // JSON.parse of pong payload
  await this.handleEventData(data);            // dataCache.mergeData -> JSON.parse
});

Any exception (frame decode failure, malformed pong, invalid fragment metadata, fragment JSON parse failure) rejects the listener promise — the event is dropped with no log, and the unhandled rejection can crash the process.

mergeData had an additional silent-loss amplifier: new Array(sum) throws a RangeError for invalid sum, and a seq outside [0, sum) creates sparse holes that produce a corrupted merged buffer (so JSON.parse fails and the event is lost).

Changes

• ws-client/index.ts
  • communicate(): wrap the whole inbound-frame handler in try/catch and log failures (failed to handle inbound frame: ...) instead of dropping them silently or surfacing them as unhandled rejections.
  • handleEventData(): catch fragment-merge failures and log them with message_id / trace_id so operators can reconcile.
  • handleControlData(): guard the pong JSON.parse and log malformed payloads.
• ws-client/data-cache.ts: validate fragment metadata (sum integer > 0, seq in [0, sum)) before allocating/merging, so malformed metadata throws a clear error instead of corrupting the buffer.
• ws-client/__tests__/receive-events.ts (new): 8 tests covering decode-failure logging with connection survival, malformed fragment metadata, malformed pong, the happy path (fragmented event merges → dispatches → ACKs), and DataCache.mergeData validation.

Verification

• npx jest --runInBand ws-client channel — 32 suites, 325 tests passing (including the 8 new ones), 0 failures.
• Behavior on success is unchanged; the fix only adds error surfacing and guards.