Bulk hydrate shell snapshots in the web store

[mjc]

What Changed

Changed shell snapshot sync from N single-thread writes into one bulk pass that builds thread IDs, project indexes, shell records, session records, turn state, and sidebar summaries together.

Why

The old path repeatedly spread growing maps while hydrating large snapshots. On the synthetic 10,000-thread fixture, that made startup spend seconds in web store hydration.

Chrome first-load click profile against a synthetic 10,000-thread home (100 projects x 100 threads, 0 activities/thread, projected seed). Each side used 5 measured runs, and each run seeded a fresh synthetic home before Chrome opened Startup Thread 29/69. Table shows medians:

metric	main	after	delta
initial render	4956.4 ms	2568.6 ms	-2387.8 ms (-48.2%)
click settle	9658.0 ms	9221.2 ms	-436.8 ms (-4.5%)
total	14702.0 ms	11939.9 ms	-2762.1 ms (-18.8%)
RunTask	4383.6 ms	2179.2 ms	-2204.4 ms (-50.3%)
FunctionCall	3302.9 ms	1116.1 ms	-2186.8 ms (-66.2%)
UpdateLayoutTree	662.3 ms	651.1 ms	-11.2 ms (-1.7%)

UI Changes

No visual UI changes.

Checklist

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

Verification:

• bun fmt
• bun lint
• bun typecheck
• bun run test

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Note

Medium Risk
Moderate risk because it rewrites syncEnvironmentShellSnapshot to rebuild multiple thread-related indices/maps in one pass; mistakes could drop/reshuffle thread bookkeeping or sidebar data during bootstrap. Adds tests and keeps detail slices only for threads present, but changes touch core state hydration behavior.

Overview
Shell snapshot hydration is rewritten to run as a single bulk pass. syncEnvironmentShellSnapshot now builds threadIds, threadIdsByProjectId, threadShellById, threadSessionById, threadTurnStateById, and sidebarThreadSummaryById directly while iterating snapshot.threads, instead of repeatedly applying per-thread writes.

During sync it deduplicates duplicate thread IDs (keeps first occurrence), retains existing per-thread detail slices only for threads still present in the snapshot, and initializes the new thread maps with Object.create(null) to safely accept server-provided IDs like __proto__.

Adds focused tests for bulk shell sync covering project indexing, bootstrap completion, detail-slice retention/removal, deduplication behavior, and prototype-pollution-style IDs.

^{Reviewed by Cursor Bugbot for commit 7392fca. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Bulk hydrate shell snapshots in the web store with deduplication and safe key handling

• Rewrites syncEnvironmentShellSnapshot in store.ts to build all thread maps in a single pass over the snapshot rather than iterating and calling writeThreadShellState per thread.
• Deduplicates threads with the same id by keeping the first occurrence, constructing threadIds, threadIdsByProjectId, and shell-derived maps in first-seen order.
• Uses createRecord (null-prototype objects via Object.create(null)) so keys like __proto__ are stored verbatim without triggering prototype pollution.
• Retains existing per-thread detail slices (messages, activities, diffs, etc.) only for threads still present in the incoming snapshot.
• Adds tests in store.test.ts covering project indexing, detail slice retention, duplicate thread handling, and unsafe key storage.

^{Macroscope summarized 7392fca.}

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Refactors shell snapshot syncing to build thread indexes/maps in a single pass (with deduplication) while retaining existing per-thread detail slices, and adds tests to lock in the intended behavior.

Changes:

• Replaces incremental writeThreadShellState updates with direct construction of threadIds, threadIdsByProjectId, and per-thread shell/session/summary records during shell snapshot sync.
• Retains existing thread-scoped detail records only for threads that remain present in the snapshot.
• Adds Vitest coverage for shell snapshot syncing, including malformed duplicate thread entries.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
apps/web/src/store.ts	Builds thread indices and shell-related records directly from the shell snapshot and retains thread-scoped detail slices via filtering.
apps/web/src/store.test.ts	Adds tests for shell snapshot sync behavior (indexing, retention, and deduplication).

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[macroscopeapp]

Approvability

Verdict: Approved

Performance refactor that builds shell snapshot state in a single pass rather than iteratively. The change is internal to state construction, uses secure null-prototype records, and includes comprehensive tests. No runtime behavior changes.

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