perf(server): stop remapping every thread on each thread event

[t3dotgg]

Requested by Theo · project thread

What Changed

• updateThread in apps/server/src/orchestration/projector.ts now finds the thread's index and copies the array (slice() plus one slot write) instead of running threads.map with a callback over every thread. It returns the same array when the thread isn't found.
• thread.message-sent and thread.activity-appended already ran threads.find before updateThread, so each streaming delta scanned the threads array twice. They now look up the index once and patch it with patchThreadAt.

Why

The engine's command read model runs projectEvent for every thread event, streaming deltas included. Its threads array holds every thread the server has seen, including deleted ones, because the decider needs them. On an install with about 5k threads, that meant a full callback map on every delta.

At 5k threads, with the streaming thread near the end of the array (the usual case), the helper goes from about 67µs to 43µs per event. projectEvent for a message delta takes about 25% less time, from about 111µs to 84µs. Those numbers were measured before the single-scan change, which removes one more linear scan per delta.

This is a CPU win, not a memory win. slice() still allocates a full-length array on every event. To get rid of that copy and the linear lookup, the read model would need to key threads by id, which is a broader change.

Checks: projector, decider and OrchestrationEngine tests (181 passed), plus server tsc --noEmit and vp lint on the changed file.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes (n/a)
• I included a video for animation/interaction changes (n/a)

Done with Claude Code (Opus 5.5).

🤖 Generated with Claude Code

https://claude.ai/code/session_01Apa4PipuLUNhbdABEvHXJB

Summary by CodeRabbit

• Bug Fixes
  • Thread updates now affect only the matching thread, leaving other threads unchanged. If the requested thread isn’t present, the existing thread list remains unchanged. Message and activity updates are also applied to the thread they belong to, helping keep conversation data consistent as updates arrive.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.5 KiB	+15 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	−3 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.5 KiB	+18 B (+0.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	56.3 KiB	+44 B (+0.1%)	66.4 KiB	✅
Codex	Live turn messages	9	10	+1 (+11.1%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	+10 B (+0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	−3 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	+13 B (+0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: ed809f7 · PR result: b68cc2a · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 114.0 KiB
• Claude decoded thread snapshot: 114.7 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[macroscopeapp]

Approvability

Verdict: Approved at b68cc2a

Macroscope's review found this PR approvable — This is a focused server-side performance refactor that reduces redundant thread-array scans during streaming and other events while preserving projected thread data and ordering. It changes only one production source file and introduces no new capability, schema impact, default change, or static-analysis override.

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📥 Commits

Reviewing files that changed from the base of the PR and between a9b335c and b68cc2a.

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• apps/server/src/orchestration/projector.ts

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📝 Walkthrough

Walkthrough

updateThread locates a matching thread and delegates the patch to patchThreadAt. The message-sent and activity-appended handlers retain the index from their lookup and use it to patch the thread.

Changes

Thread Update

Layer / File(s)	Summary
Thread array patching apps/server/src/orchestration/projector.ts	updateThread delegates to patchThreadAt, which shallow-copies the array and patches the indexed thread. The message-sent and activity-appended handlers retain the thread index and use it to patch messages or activities and the timestamp.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~5 minutes

Change: Refactor

Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to b68cc

The thread updates continue to target the correct thread without mutating the original array. No material merge risk was identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly and concisely describes the main performance change: avoiding a full thread remap for each thread event.
Description check	✅ Passed	The description includes the required What Changed, Why, and Checklist sections. It explains the implementation, performance motivation, testing, and UI checklist status. The description is complete a…

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Dismissing prior approval to re-evaluate b68cc2a