Show thread numbers in sidebar

[ryanbbrown]

Closes #1243.

Summary

• add a browser-local Thread numbers option to the sidebar display menu
• keep the option off by default and remember it in local storage
• show subtle, fixed-width 1–9 prefixes beside the first nine rendered thread rows
• update the numbers when rows mount, move, or unmount so they match the existing thread jump shortcuts
• observe sidebar changes only while numbers or keyboard shortcut hints are visible

User impact

Thread numbers stay hidden by default. A user can open the sidebar display menu and select Thread numbers. The choice applies to that browser instead of every bb client.

Testing

• pnpm exec turbo run test --filter=@bb/app -- --run src/components/sidebar/ThreadRow.test.tsx src/components/sidebar/sidebarThreadShortcuts.test.ts src/components/sidebar/SidebarViewOptionsMenu.test.tsx
• pnpm exec turbo run typecheck --filter=@bb/app
• pnpm exec turbo run lint --filter=@bb/app (passes with existing warnings)
• git diff --check

[bb-slop-cop]

🚨 SLOP COP 🚨 · review

I am SlopCop. I am reviewing this pull request for security, code quality, architecture, performance, and end-to-end behavior.

[bb-slop-cop]

🚨 slopcop/review — Avoid the observer when both thread displays are inactive.

Please observe only when numbers are enabled or the command modifier is held. The default state still scans every sidebar child-list change. Target changes also replace the context map and render all mounted rows with unchanged output. Clear the assignments and target reference when this observer stops.

[bb-slop-cop]

🚨 SLOP COP 🚨 · review

ELI5 summary

This change adds an optional number beside each of the first nine sidebar threads. The numbers match the existing keyboard shortcuts.

Findings

1. Medium priority: the app always observes the full sidebar subtree. It does this when numbers are off and no modifier key is held. Each child change scans the subtree. It can also render every mounted thread row again. I left an inline comment with a focused fix.

2. Merge blocker: current main already contains 0093_peaceful_thing. This pull request adds a different migration at index 0093. GitHub reports a merge conflict. Rebase the branch, then use Drizzle to generate migration 0094, its snapshot, and its journal entry.

I found no security issue. I found no duplicate implementation. The shared sidebar shortcut module is the correct location for this logic.

Checks

• All 116 focused app, CLI, database, and server tests passed.
• Type checks passed for the app, CLI, server, database, and domain packages.
• Browser tests showed no numbers by default.
• The setting showed exactly 1 through 9 for ten threads.
• Control+1 opened the first numbered thread.
• The CLI disabled the setting, and the open app removed the numbers.
• GitHub CI passed against the old base.

I posted this as a comment review. I did not approve or request changes.