fix: cap session tab title length

[pi-claw-agent]

Summary

Session editor-tab titles now pass through a deterministic code-point-based length cap (28 chars plus ellipsis, whitespace collapsed) applied in the shared tab-title builder, so streaming and idle states always produce the same label length and one long conversation can no longer crowd sibling tabs out of view. Added focused unit tests for truncation, surrogate safety, and the shared builder, plus source assertions locking equal-length caps for both tab states.

Validation

• bun install --frozen-lockfile
• bun run check-types
• bun run lint
• bun run compile-tests
• bun esbuild.js
• bun esbuild.webview.js
• xvfb-run -a bun x vscode-test (189 passing)
• git diff --check

Closes #63

[pi-claw-agent]

Independent Agent review: approved

Review round 1/2 for 59832c895382.

Session editor-tab labels now flow through a single capped builder (28 code points plus ellipsis, whitespace collapsed) used identically for streaming and idle states, so a long conversation can no longer push sibling tabs out of view and activation does not change label length. Unit tests cover truncation, surrogate safety, whitespace collapse, and the shared-builder wiring.

Findings

• minor: Cap comparison uses UTF-16 length while slicing counts code points — src/tab-label.ts:15
  • Evidence: `compact.length <= maxLength` counts UTF-16 code units, but the truncation branch slices by code points. A label with exactly 28 code points that contains astral characters (e.g. '\u{1F600}'.repeat(28)) has 56 code units, so it takes the truncation branch and gains an unnecessary '…' (29 displayed) while an equally long ASCII label of 28 code points stays unadorned (28 displayed). Verified against the compiled module.
  • Recommended fix: Compare against the code-point count (e.g. Array.from(compact).length or a spread) in the length guard so the cap decision and the slice share one unit, keeping exact-cap labels free of a spurious ellipsis.

Reviewer checks

• Inspected git diff main...59832c8 and traced every panel.title assignment through the shared tab-title builder, plus fallback labels and streaming-state updates.
• bun run compile-tests
• ./node_modules/.bin/mocha --ui tdd out/test/tab-label.test.js (5 passing)
• ./node_modules/.bin/eslint src/test/tab-label.test.ts src/tab-label.ts
• bun run check-types
• node compiled-module boundary probes for astral characters at the cap (no surrogate splitting, unnecessary ellipsis at exact code-point cap confirmed)
• git diff --check main...59832c8

Generated by the independent sandboxed Reviewer Agent. The PR still requires human review and merge.