Fix Update tooltip keyboard navigation - #330176

…ures (PRD 0013) (#282)

Executes docs/prd/0013-upstream-port-1.127-to-1.135.md end to end: 183 commits cherry-picking/adapting the fork-relevant subset of the 3,672-commit upstream delta (microsoft/vscode b0b6062..07c20d9, 1.127.0→1.135.0), in four waves.

## Waves (issues #249–#280)
- **Wave 1 — security (#249–#255):** upstream security rollup microsoft#330308 (env-var hardening incl. DYLD_INSERT_LIBRARIES, URL-handler trust ordering, domain-matcher bypass + fail-open fix), loopback OAuth XSS, MSRC web-worker iframe parentOrigin, trusted-domain backslash bypass, stale-secrets purge, chat-import path traversal, fetch-tool approval bypasses, skill-name prompt-injection escaping, Electron 42.3.0→42.8.1 (six Chromium security trains, download checksum-verified), markdown-it 12→14.
- **Wave 2 — live product bugs (#256–#261):** cache_control sentinel no longer leaked to non-aware BYOK providers (vendor allow-list incl. flowleap-trial, fail-closed), session cap 50→400, darwin updater late-error guard, disposed-frame crash guards, duplicate file-ops from scoped editor services, sessions quartet (Changes spinner, picker close, grouping leak, archived-terminal disposal), worktree branch/path collision race (our code, regression-proven tests).
- **Wave 3 — mechanical batch (#264–#269):** ~95 upstream commits: terminal/workbench/chat/base leak sweeps, disposal crash guards, base correctness primitives with tests, streaming-markdown repair, :has() CSS perf fix, ListView/toolbar batching, MCP robustness + plugin-marketplace TTL refresh, gallery hardening.
- **Wave 4 — UX features (#270–#280):** chat Ctrl+F find widget, update-service rewrite (update.mode live, metered deferral; ADR-0008 invariants verified), model-selection robustness (fixes live Trial-provider remembered-model loss), sessions QoL (rename/reopen/middle-click/mouse-nav/OS notifications), turn timestamps, token-stats consumer, PromptsStorage.builtIn seam (45 bundled skills verified at runtime), clipboard architecture (rich HTML + Markdown copy), response disclosure + thinking/streaming UX, save-dirty/confirm-discard/image+vision fixes, go-to-symbol, scroll persistence, cache-break hint, sticky scroll.

## Validation
- Full unit suite at tip: **21,811 passing / 0 failing** (389 pending); valid-layers-check, core + extension typechecks clean.
- Rebased onto latest main (zero conflicts, zero file overlap with the base move).
- Electron 42.8.1 download validates against ported checksums; smoke-tested live (find widget, updater disabled-in-dev invariant, gallery 404 grace).
- Known flake: McpStdioStateHandler stdin test can fail under full-suite machine load; passes deterministically in isolation.

## Notes for reviewers
- Deliberate skips (Modern UI, single-pane layout, dictation, Automations, asar re-pack, tsgo→tsc) are documented in the PRD with evidence per issue report.
- Follow-ups filed in issue reports: token-stats producer wiring, closed-chat state on session eviction, views.css :has() selector, microsoft#330176 tooltip keyboard nav.

Closes #249, closes #250, closes #251, closes #252, closes #253, closes #254, closes #255, closes #256, closes #257, closes #258, closes #259, closes #260, closes #261, closes #264, closes #265, closes #266, closes #267, closes #268, closes #269, closes #270, closes #271, closes #272, closes #273, closes #274, closes #275, closes #276, closes #277, closes #278, closes #279, closes #280

https://claude.ai/code/session_01RWkt8yKCBKXjTN7bdqaK9o