* perf(plugins): cache existence probes within bundle manifest scan
Bundle plugin discovery re-probes the same marker paths (skills/, commands/,
agents/, .mcp.json, .lsp.json, settings.json, hooks/hooks.json) once in
detectBundleManifestFormat and again in loadBundleManifest's capability
builders. Across the bundled plugin tree this is thousands of redundant
synchronous fs.existsSync calls; #76209 reports 25.4s of self-time on a
Windows cold start.
Add a scan-scoped existence cache (plugin-scan-existence-cache.ts) entered
only around discoverBundleInRoot. pluginScanExistsSync memoizes inside the
active scan and falls back to plain fs.existsSync outside it, so install,
hooks, and doctor flows stay uncached. The cache is push/pop per
discoverBundleInRoot call (try/finally), so a later install/repair pass
re-reads the filesystem — no process-global staleness.
Measured on Windows over a 25-plugin fixture: 550 -> 325 fs.existsSync
calls (41% fewer), 294.75ms -> 208.49ms. Discovery results unchanged.
Closes#76209
* fix(plugins): drop unused test reset helper and satisfy oxlint
Remove __resetPluginScanExistenceCacheForTest: the scan cache is push/pop
balanced by try/finally in withPluginScanExistenceCache, so the stack never
leaks between tests and the helper was dead code. It also tripped oxlint
no-underscore-dangle. Refactor the integration test to count existsSync calls
via a const-returning helper so there is no useless assignment.
