perf(clients): saving the thread list cache no longer freezes the UI

[t3dotgg]

With thousands of threads, every save of the thread list (shell) cache ran the full snapshot through Schema encoding on the UI thread. On a synthetic 5,200-thread snapshot, that is about 76 ms per save in Node and about 470 ms in Hermes, on an M5 Max. The save runs 500 ms after every pause in shell traffic, so the UI stalled again and again while agents streamed.

Fix

• New encodeShellSnapshotForCache in client-runtime, used by the web and mobile saveShell. Projects still go through Schema, because the project icon has a real encode transform (about 0.3 ms for 60 projects). A decoded thread shell is already in its encoded form, so threads go straight to JSON.stringify.
• The result equals the full Schema encoding, so the cache format does not change. On the benchmark snapshot the saved bytes are identical. Older builds read the cache as before.
• Web writeDatabaseValue now resumes on the transaction abort event, not error. A failed commit (for example QuotaExceededError when the disk is nearly full) fires only abort, so the write never resumed. The shell save stream then waited forever, and no later shell save ran in that session. Catalog writes use the same helper.

Save timing does not change: 500 ms debounce, as before.

Earlier versions of this PR added a 10 s throttle (removed: not needed at these costs), and saved the whole snapshot as plain JSON. Plain JSON saved monogram icons in their decoded shape, which builds from before #11993 cannot read. This version does not have that problem.

Measurements

Synthetic snapshot: 60 projects (monogram, lucide, emoji, and no icon), threads with model options, a linked PR on half of them, latest turn, session, and title state. Time per save, including JSON.stringify:

Threads	JSON size	Node before	Node after	Hermes before	Hermes after
761	1.2 MB	11 ms	2.4 ms	71 ms	7 ms
5,200	8.3 MB	76 ms	14 ms	468 ms	27 ms

• Node 26, median of 30 runs.
• Hermes: the hermes CLI from the facebook/hermes v0.13.0 release (it reports 0.12.0), hermes -O, with the bundle compiled by @react-native/babel-preset. Median of 10 runs, 1 ms timer. This is not a device, and the app ships a newer Hermes, so treat these numbers as relative.

Tests

encodeShellSnapshotForCache cannot show the speedup in its output, because the output is the same by design. The new test instead checks the fact that makes the shortcut safe: for generated snapshots, the helper returns the same value as the full Schema encoding. The generator fills shell fields, including optional ones, so a later encode transform on a field it sets fails the test, also one whose decoded type still satisfies .Encoded. A deeply nested optional field is only caught when a generated value sets it, so coverage there is probabilistic.

Verification

• vp test run on client-runtime persistence.test.ts (1, new), web storage.test.ts (5), and mobile environment-cache-store.test.ts (6).
• Mutation checks: skipping the project encoding fails the new test (monogram icon shape). Adding a prefix encode transform to the thread branch field, or to the optional pinOrderKey field, fails it in 3 of 3 runs each. Listening for error instead of abort makes the web write test time out.
• The new test uses a random seed. It passed 30 of 30 repeated runs. A separate sweep of 1,761 generated thread shells found no thread whose Schema encoding differs from the decoded value.
• vp lint, vp fmt, and tsc --noEmit for client-runtime, web, and mobile.
• Not run in a real client or on a device.

Not in this PR: removeDatabaseValue and removeDatabaseValuesInRange also listen only for error. Deletes do not hit quota, but a forced database close can abort them the same way.

Made by Claude Opus 5.5 (1M context) in Claude Code, running in T3 Code.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Shell snapshots are encoded before being saved in the mobile and web apps, supporting consistent snapshot data when it is loaded later.
  • Mobile snapshot encoding and serialization failures are reported as save errors.
  • Catalog writes now detect IndexedDB transaction aborts and report write failures, including quota-related errors.

[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	−5 B (−0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	0 B (0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−5 B (−0.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	56.2 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	−25 B (−0.2%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	+9 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−34 B (−0.5%)	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: 92f0af2 · PR result: 84980ec · 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: 113.9 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: Not approved

Macroscope's review found this PR not approvable — The PR changes production web and mobile persistence behavior, including shared cache serialization and IndexedDB abort handling, and introduces a line-level diagnostic suppression. These changes are bounded and tested but warrant human review because they affect a shared runtime persistence path.

Notes:

• No code objects were reviewed. Approvability was decided on eligibility alone.

No code changes detected at 84980ec. Prior analysis still applies.

^{You can add or adjust custom eligibility rules. Learn more.}

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📝 Walkthrough

Walkthrough

Mobile and web shell snapshot save paths encode snapshot projects before JSON serialization. The web database write path handles transaction abort events and maps them to catalog write errors.

Changes

Shell snapshot cache encoding

Layer / File(s)	Summary
Snapshot encoding and save paths packages/client-runtime/src/platform/persistence.ts, packages/client-runtime/src/platform/persistence.test.ts, apps/mobile/src/connection/environment-cache-store.ts, apps/web/src/connection/storage.ts	The cache encoder encodes snapshot projects. Mobile and web save paths use the encoded snapshot before JSON serialization. A generated-value test compares the cache encoder output with schema encoding.

IndexedDB abort handling

Layer / File(s)	Summary
Catalog write abort errors apps/web/src/connection/storage.ts, apps/web/src/connection/storage.test.ts	Catalog writes now handle transaction abort events. A test checks that an abort without an error event reports the QuotaExceededError.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: 🔵 Low · up to 5755d

The cache-encoding test could fail because its generated projects were filtered out, rather than because cache encoding is wrong. This is a bounded concern, not a demonstrated production failure.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 8 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 identifies the main change: reducing UI freezes when saving the thread list cache.
Description check	✅ Passed	The description clearly explains the problem, implementation, performance results, tests, verification, and scope. It does not include the template's Checklist section, but the description is otherwis…

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[macroscopeapp]

Correction to my inline review comment on apps/web/src/connection/storage.ts: the focused-backend-tests convention does not require a web-specific test for this browser-side cache change. The mobile round-trip test provides relevant coverage, so please disregard my test request. I found no Effect service convention violation in the selected file.

^{Posted via Macroscope — Effect Service Conventions}

[coderabbitai]

🧹 Nitpick comments (1)

packages/client-runtime/src/platform/persistence.test.ts (1)

50-50: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Require at least one generated project.

sampleDecoded filters out every value that fails encode/decode. If all generated projects are filtered out, the equality assertion passes without testing the project-icon transform. Assert that projects.length is greater than zero.

Suggested fix

       expect(threads.length).toBeGreaterThan(0);
+      expect(projects.length).toBeGreaterThan(0);
       expect(yield* encodeShellSnapshotForCache(snapshot)).toEqual(yield* encodeSnapshot(snapshot));

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In `@packages/client-runtime/src/platform/persistence.test.ts` at line 50, Add an
assertion that projects.length is greater than zero in the test containing the
threads.length assertion, so the project-icon transform is tested even when
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In `@packages/client-runtime/src/platform/persistence.test.ts`:
- Line 50: Add an assertion that projects.length is greater than zero in the
test containing the threads.length assertion, so the project-icon transform is
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In `@packages/client-runtime/src/platform/persistence.test.ts`:
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