perf(mobile): reduce move-menu index allocations

[juliusmarminge]

Home rebuilds move-menu availability while threads stream. Its index construction allocated several full-size intermediate arrays for every section, even when only a handful of threads could move.

Build the existing indexes with loops, reuse each scoped ID, and use the position map for visible membership. This removes temporary arrays and a redundant Set. No cache or deferred menu state is added; move planning and duplicate-ID behavior stay the same.

Release measurements

Two alternating before/after pairs on iPhone 17 Pro, iOS 27 simulator. Home visible with 1,210 thread shells; five streams at 20 Hz for 15 seconds, 1,500 events per run. Each run restores the same server snapshot and app cache. Optimized Release native executable, Hermes -O, dev=false, no Metro server. Source-map comparison confirms only threadOrder.ts differs. Baseline fbb9943, candidate 510e5bb.

Measurement	Before 1	After 1	Before 2	After 2
Move-availability inclusive samples	299	131	299	123
Active JS samples	2,555	2,424	2,670	2,604
Total samples	14,782	14,900	15,115	15,113
GC samples	390	316	363	294
Process CPU seconds	4.88	4.68	4.82	4.74
Capture seconds	22.94	22.89	22.92	22.94

Mean process CPU fell from 4.85 s to 4.71 s, about 3% for this workload. Move-availability samples fell about 58%. Two pairs are limited evidence, not a confidence interval. Samples are not milliseconds; process CPU includes native threads and profiler overhead. No whole-app latency or battery claim.

evidence.json · move-index-after-1.cpuprofile · move-index-after-2.cpuprofile · move-index-before-1.cpuprofile · move-index-before-2.cpuprofile

Verification

117 focused tests across move availability, list construction, drag gaps and order state pass. This includes 4,000-seed planner parity and adversarial hidden-key cases. Targeted lint and mobile typechecking pass. The index loops retain last-key/last-index Map semantics and reserve keys only after the final per-ID key is known.

Shared iOS/Android Home logic; runtime measurements are iOS simulator only. No server, protocol, provider, web or desktop changes. Unrelated widget edits are excluded. No visible UI change is intended.

Julius requested one PR per measured mobile performance hotspot in this maintainer audit.

Implementation: Claude Opus 5.5 through T3 Code. Integration, review and release profiling: GPT-6 Astra through the Codex harness.

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[macroscopeapp]

Approvability

Verdict: Approved at 510e5bb

Macroscope's review found this PR approvable — This is a small, self-contained performance refactor that replaces intermediate collection allocations with equivalent loops in the mobile move-menu calculation. It preserves existing behavior, has no product-default or static-analysis changes, and is covered by parity tests.

Notes:

• Diff unchanged. Approvability was decided on eligibility alone.

No code changes detected at 1cab7ba. Prior analysis still applies.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	4.9 KiB	—	6.8 KiB	✅
Codex	Thread snapshot wire	—	3.8 KiB	—	4.9 KiB	✅
Codex	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Codex	Live turn WebSocket decoded	—	20.8 KiB	—	29.3 KiB	✅
Codex	Live turn messages	—	1	—	8	✅
Claude	Total thread wire	—	5.0 KiB	—	6.8 KiB	✅
Claude	Thread snapshot wire	—	3.8 KiB	—	4.9 KiB	✅
Claude	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Claude	Live turn WebSocket decoded	—	21.2 KiB	—	29.3 KiB	✅
Claude	Live turn messages	—	2	—	8	✅

Baseline: unavailable · PR result: 1cab7ba · 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: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

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

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📥 Commits

Reviewing files that changed from the base of the PR and between fbb9943 and 510e5bb.

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• apps/mobile/src/features/threads/threadOrder.ts

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📝 Walkthrough

Walkthrough

computeThreadMoveAvailability now uses explicit loops to build ordered IDs and indexes, key and writability lookups, and reserved keys. For duplicate IDs, reservation uses the final key stored in keysById.

Changes

Thread move availability

Layer / File(s)	Summary
Build thread move availability apps/mobile/src/features/threads/threadOrder.ts	computeThreadMoveAvailability builds ordering and lookup data with loops. For duplicate IDs, the final key in keysById determines whether that key is reserved.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to 510e5

No actionable merge-blocking risk is established for this allocation-focused change; the reported focused tests support preserving move-availability behavior.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: reducing move-menu index allocations on mobile.
Description check	✅ Passed	The description clearly covers the problem, change, and verification, with detailed measurements and test results. It states that a maintainer requested the work, but does not link to the audit or inc…
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
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.

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Dismissing prior approval to re-evaluate 510e5bb