Make sidebar disclosure project-specific and child-aware

[jshph]

Human comments

What was wrong

The sidebar progressive-disclosure experiment also limited By machine lists, and its initial project selection followed the display sort instead of considering activity within each thread tree. Expanded project lists had no Show less control.

What changed

Restrict progressive disclosure to By project. Select five ordinary root trees using the latest attention timestamp among their idle or errored descendants, while keeping trees needing attention or containing the selected thread visible. Preserve the configured display order, reveal ten more trees per Show more click, and add Show less to reset the revealed set. By machine and Manually remain fully expanded.

Update the experiment label and configuration/CLI guidance. The experiment remains off by default; enable it in Settings → Experiments or with bb settings experiment sidebarProgressiveDisclosure true. This change uses existing timestamps and adds no database migration or protocol changes. Successful child completion does not independently update the attention timestamp used for ranking.

How you verified

• pnpm exec turbo run test --filter=@bb/app -- --run src/components/sidebar/ProjectThreadTree.disclosure.test.tsx src/components/sidebar/ProjectList.modes.test.tsx — 21 tests passed, covering disclosure selection, expansion/collapse, and organization modes.
• pnpm exec turbo run typecheck lint --filter=@bb/app — passed; lint reported 198 warnings and no errors.
• Compared the rebased contributor commit with its original commit; differences preserve main's newer sidebar grouping and tests. Browser verification was not repeated for this restored revision.

AGENT GENERATED