[TheJavaGuy]

Summary

Shows a session's title instead of its first user message in the sidebar, tab labels and command palette.

This reimplements Part B of upstream matt1398#129. That PR can't be applied as-is:

• It conflicts with current main.
• It adds a second full read of every session file (extractCustomTitle()).
• It only reads custom-title lines. Current Claude Code also writes {"type":"agent-name","agentName":"..."} (session name) and {"type":"ai-title","aiTitle":"..."} (auto-generated title).

Title precedence:

1. Last non-empty agent-name / custom-title entry
2. Otherwise the last non-empty ai-title
3. Otherwise the first user message (the old behavior)

Changes

• analyzeSessionFileMetadata (src/main/utils/jsonl.ts): picks up title entries in its existing single streaming pass and returns customTitle. No extra file read and no new cache.
• Session.customTitle is filled by both ProjectScanner session builders.
• getSessionTitle() (new src/renderer/utils/sessionTitle.ts): used by SessionItem, CommandPalette and the tab label logic.
• Tab labels (sessionDetailSlice):
  • Synced for every tab showing the session, on initial fetch and on in-place refresh.
  • On refresh, the sync runs before the chunk-fingerprint early return. A rename only appends a title line and doesn't change chunks, so the early return would otherwise skip it.
• Manual tab renames: renaming a tab by hand (SortableTab) now sets Tab.labelSetByUser, and the automatic sync skips flagged tabs. Without this flag, any refresh would overwrite a hand-set tab name.

Tests

• test/main/utils/jsonl.test.ts covers title parsing:
  • agent-name, custom-title, and ai-title only
  • user title beats ai-title regardless of line order
  • last rename wins
  • empty or whitespace titles are ignored
  • no title lines gives undefined
  • title lines don't change messageCount
• test/renderer/utils/sessionTitle.test.ts covers getSessionTitle.
• test/renderer/store/sessionDetailSlice.test.ts covers:
  • tab label on fetch
  • label update on refresh when chunks are unchanged
  • a hand-set tab label is kept
• pnpm typecheck, pnpm lint (no errors) and pnpm test (750 tests) pass.
• Ran analyzeSessionFileMetadata on real session files: add-healthy-food-plugin (agent-name) and Two envelopes switching simulation (ai-title).