fix(telemetry): serialize each event once at admission

[youtsuhodev]

Description:

Serialize each telemetry event exactly once, at admission, instead of three
times across the emit → flush path.

BufferedMatchTelemetryEmitter.emit() previously ran JSON.stringify(event)
and then JSON.parse(serialized) purely to deep-clone the event for its
admission snapshot, and sendBatch() later re-stringified every queued event
inside the batch envelope. For intent_observed — emitted per accepted/rejected
intent, up to 10/s per client — this put three serialization passes on a hot
path.

Changes in src/server/telemetry/BufferedMatchTelemetryEmitter.ts:

• QueueEntry now stores the admission-time JSON string (serialized) instead
  of the event object. That string is both the immutable snapshot and the exact
  wire payload, so the JSON.parse clone is gone.
• emit() computes bytes from that single string; the byte budget, oversized
  event, and circular-reference (droppedSerialization) behavior are unchanged.
• sendBatch() splices the pre-serialized fragments into the envelope by
  concatenation (same key order and values as the previous JSON.stringify of
  the object), removing the second serialization of every event.

Net effect: two serialization passes removed per intent, no JS deep clone, and
the large intent object is no longer retained in the queue.

Scope: performance-only, no wire-format or signature change. Verified the emitted
batch is byte-for-byte compatible with the previous envelope (HMAC signature is
computed over the body exactly as before).

Testing: npx vitest tests/server/telemetry tests/server/MatchTelemetryIntegration.test.ts --run
→ 37 passed. oxlint and eslint clean on the changed file. No new tests were
added: the existing suite already covers the affected paths (immutable admission
snapshot after caller mutation, exact serialized byte budget, unserializable/
circular event dropped without throwing, FIFO batch + exact HMAC).
No src/core changes.

Please complete the following:

• I have added screenshots for all UI updates
• I process any text displayed to the user through translateText() and I've added it to the en.json file
• I have added relevant tests to the test directory

Please put your Discord username so you can be contacted if a bug or regression is found:

lilian.looters

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: ba953e38-2337-4e26-9384-11977f956760

📥 Commits

Reviewing files that changed from the base of the PR and between 1e973bb and 1ac9d2a.

📒 Files selected for processing (1)

• src/server/telemetry/BufferedMatchTelemetryEmitter.ts

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Walkthrough

BufferedMatchTelemetryEmitter now serializes each telemetry event once during emission. The queue stores that serialized JSON and its byte length. Batch submission joins the stored JSON fragments into the request body without re-stringifying event objects.

Changes

Telemetry serialization

Layer / File(s)	Summary
Serialized queue and batch submission src/server/telemetry/BufferedMatchTelemetryEmitter.ts	QueueEntry stores serialized JSON instead of an event object. emit removes the parse round-trip. sendBatch joins the stored JSON fragments into the request envelope.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Refactor

Suggested reviewers: celant

Merge Risk: ⚪ Minimal · up to 1ac9d

The telemetry optimization preserves the existing event payload and delivery behavior, so it is mergeable with normal checks.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: serializing each telemetry event once during admission.
Description check	✅ Passed	The description directly explains the serialization change, preserved behavior, performance impact, testing, and scope.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

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_{JSON rests in the queue,
Bytes keep the count in view,
Events cross the wire,
No second parse required,
Batches join their parts,
Telemetry keeps its course.}

_{Comment @coderabbitai help to get the list of available commands.}

[github-actions]

🤖 Claude Code Review

Verdict: ✅ No issues found — this is a clean, correct performance-only refactor.

Findings by severity: Critical: 0 · High: 0 · Medium: 0 · Low: 0

Summary:

The change to src/server/telemetry/BufferedMatchTelemetryEmitter.ts replaces the JSON.stringify → JSON.parse deep-clone in emit() and the second JSON.stringify of the whole batch in sendBatch() with a single admission-time serialization, storing QueueEntry.serialized: string instead of QueueEntry.event. The batch envelope is now built by string concatenation instead of object serialization.

I independently verified:

• Byte-for-byte compatibility: the hand-built envelope (schemaVersion, batchId, createdAt, server, events) preserves the exact key order and encoding of the original JSON.stringify(...) call. batchId and server are still passed through JSON.stringify, so quoting/escaping is unchanged; createdAt (a number) serializes identically either way.
• JSON-injection safety: each entry.serialized fragment is guaranteed to be the output of a prior successful JSON.stringify(event) call (validated at admission before being queued), so it's always a single, syntactically valid, self-balanced JSON value — joining fragments with , inside [...] cannot break out of the array structure.
• Immutability guarantee preserved: the admission-time string is naturally immune to later mutation of the original event object, same as the old deep-clone-via-parse approach.
• Byte accounting, drop paths, and HMAC signing are unchanged — the signature is still computed over the exact body string sent, and the droppedSerialization/serialization_failed error paths remain reachable.
• CLAUDE.md compliance: the only changed file lives under src/server/, not src/core/, so the 'all src/core changes must include tests' rule doesn't apply. No user-visible text is touched, so the i18n rule is not implicated. No violations found.

No high-signal bugs, logic errors, or CLAUDE.md violations were identified in this diff.

🤖 Generated with Claude Code