perf(lifecycle): scope extension timer builtins

[JustYannicc]

What changed

• Route extension require('timers'), require('node:timers'), require('timers/promises'), and require('node:timers/promises') through lifecycle-scoped timer facades when loadExtensionExport has a TimerRegistry.
• Preserve setImmediate/clearImmediate and timers/promises async iterator/scheduler APIs while tracking pending handles in the ExtensionView registry.
• Extend the lifecycle sandbox harness with imported timer before/after leak coverage and fired one-shot pruning checks.

Why

Imported Node timer built-ins could bypass ExtensionView cleanup and keep intervals/timeouts alive after unmount or no-view background completion. Bare wrapper timers were already scoped; imported timer modules now use the same lifecycle registry.

Compatibility impact

• Scoped behavior applies only when loadExtensionExport has a TimerRegistry.
• Unscoped built-in fallback behavior remains on the existing real Node/static stub path.
• Raycast-style timers, node: aliases, setImmediate, clearImmediate, timers/promises setTimeout, setInterval async iteration, setImmediate, and scheduler.wait remain available.

How tested

• node scripts/test-extension-lifecycle-sandbox.mjs
• node scripts/test-extension-wrapper-cache.mjs
• npm run typecheck:renderer attempted, but local npm is intentionally disabled and rerouted to pnpm; repo parity rejected pnpm. Ran direct equivalent: ./node_modules/.bin/tsc -p tsconfig.renderer.json --noEmit --pretty false
• Codex LSP diagnostics on src/renderer/src/ExtensionView.tsx: no diagnostics found
• Codex LSP references for createExtensionLifecycleScope checked expected production/facade call sites
• git diff --check

Performance evidence

• Harness pre-fix imported timer module path: beforeClear { intervals: 1, timeouts: 3, total: 4 }, after clear unchanged at total 4.
• Harness scoped facade path: beforeClear { intervals: 1, timeouts: 3, total: 4 }, registryBeforeClear { intervals: 1, timeouts: 3 }, after clear total 0.
• Fired imported one-shots: 4 scheduled handles pruned to registryTimeoutsAfterFlush 0 and hostTimeoutsAfterFlush 0.

Stack validation

• Started from codex/perf-wave4-integrated-stack-20260705 at ac90ce4 and branched to codex/perf-lifecycle-scoped-timer-builtins-20260705.
• Changed files: src/renderer/src/ExtensionView.tsx; scripts/test-extension-lifecycle-sandbox.mjs.
• Temporary sibling node_modules symlink was used for local checks because this worktree had no dependencies; it was removed before commit.

Replaces

• Supersedes the audit finding that imported extension timer modules could prefer real Node built-ins or global stubs and outlive ExtensionView lifecycle cleanup.

[JustYannicc]

Superseded by the consolidated runtime/lifecycle/media PR: #622