perf(web): avoid repeated terminal metadata scans

[leoisadev1]

Problem

Each sidebar and status-indicator consumer rescanned terminal metadata, rebuilt session wrappers, and resorted IDs. The work repeated for every thread that only needed running-subprocess IDs.

Changes

Build one ordered metadata index per immutable snapshot. Reuse unchanged session wrappers and thread groups across snapshots while keeping environment targets separate. Attached-terminal subscriptions and state remain unchanged.

Adapted from pingdotgg#9747.

Verification

• vp test run apps/web/src/state/terminalSessions.test.ts: 6 passed.
• Web typecheck passed.
• Scoped lint, formatting, and git diff --check passed.

The tests cover numeric ordering, stable ties, changed and removed sessions, structural reuse, environment isolation, stable empty results, and one metadata scan across many thread selectors.

Implemented and verified by GPT-5.6 Sol in T3 Code via the Codex harness.

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1 Skipped Deployment

Project	Deployment	Actions	Updated
akeru-bot-landing	Skipped		Sep 10, 2026 6:26pm UTC

[greptile-apps]

Greptile Summary

This PR optimizes web terminal-session derivation by building one ordered metadata index per immutable snapshot and reusing session wrappers and thread views when their inputs are unchanged.

• Adds snapshot-, environment-, and thread-aware structural reuse.
• Reuses the metadata index for attached-session lookup.
• Memoizes running-subprocess ID derivation.
• Adds coverage for ordering, changed and removed sessions, environment isolation, stable empty results, and scan count.

Confidence Score: 5/5

Safe to merge.

No outstanding findings require changes.

_{Reviews (3): Last reviewed commit: "Merge remote-tracking branch 'origin/mai..." | Re-trigger Greptile}

[leoisadev1]

This is Leo's agent. Independent review of e2355ba: 50 focused selector, terminal-stream, drawer and status tests pass. I have not found a correctness defect in the cache. However, I cannot establish the advertised performance benefit on the current product path: AppSidebarLayout renders BotRosterSidebar; useThreadRunningTerminalIds is used by the retained Sidebar, LegacySidebar and otherwise-unused ThreadRowTrailingStatus; useAttachedTerminalSession is used by ThreadTerminalDrawer, whose component has no production caller found. SettingsFontPreviews imports only its theme helper. Please identify the supported live caller before this is accepted as a performance port. Do not revive legacy UI or expand the feature just to exercise this optimization. This is a reachability/port-fit hold, not a claim that the passing tests prove a current-app speedup.