fix(doctor): resolve MSYS executable paths (#3865)

docs/architecture/KEY_FILES.md

@@ -56,6 +56,7 @@ per-release `**vX.Y.Z:**` narration — CI enforces this
 - `src/core/disk-walk.ts` — `walkBrainRepo(repoPath)` returns `Map<slug, {size, mtimeMs}>` from one recursive `readdirSync`. Skips dot-dirs, `node_modules`, non-`.md` files. Used by `gbrain storage status` to replace per-page `existsSync + statSync` (~400K syscalls on 200K-page brains → tens).
 - `src/core/git-head.ts` — local git HEAD freshness probe for `gbrain doctor`. `isSourceUnchangedSinceSync(localPath, lastCommit, opts?)` returns true iff `localPath` is a git repo whose current HEAD matches `lastCommit`; when `opts.requireCleanWorkingTree` is true also requires a clean working tree (mirrors `gbrain sync`'s force-walk gate at `sync.ts:1075` so doctor and sync agree on "is there work to do?"). `requireCleanWorkingTree` is `boolean | 'ignore-untracked'` — in `'ignore-untracked'` mode the clean probe runs `git status --porcelain --untracked-files=no` so a quiet repo with stray untracked dirs (`?? companies/`, `?? media/`) is still "unchanged" (sync's incremental path keys off the commit diff and never imports untracked files); `GitCleanProbe` gains an `ignoreUntracked?` second arg. Two probe seams (`_setGitHeadProbeForTests`, `_setGitCleanProbeForTests`) keep unit tests R2-compliant (no `mock.module`). Uses `execFileSync` with array args so shell metachars in `local_path` cannot escape to a shell (the regression test runs real `execFileSync` against `'/nonexistent/$(touch <sentinel>)/repo'` and asserts the sentinel is never created). Fail-open on every error (missing path, not a git repo, git not installed, timeout, NULL inputs, dirty-probe errored → false) preserving the caller's prior time-based behavior. The chunker-version-match check lives in the caller (doctor.ts) because it depends on engine state (`sources.chunker_version` vs `CHUNKER_VERSION` from `src/core/chunkers/code.ts`). Pinned by `test/core/git-head.test.ts` (incl. the shell-injection regression guard).
 - `src/core/source-health.ts` — per-source health metrics for `gbrain sources status` + doctor's `federation_health`. Commit-relative staleness: `newestCommitMs(localPath)` = HEAD committer time via `git log -1 --format=%ct` (fail-open null; NO working-tree mtime parsing — committed content only, robust against the porcelain-mtime bug farm); pure `lagFromContentMs(contentMs|null, lastSyncMs|null, nowMs)` = remote/column comparator (null lastSync → null; negative wall-clock → skew passthrough; `contentMs <= lastSync` → 0; else/null-content → wall-clock). `computeAllSourceMetrics(engine, sources, {probeContent?})`: LOCAL (`probeContent:true`, `gbrain sources status`) → `isSourceUnchangedSinceSync(..., {requireCleanWorkingTree:'ignore-untracked'}) ? 0 : wall-clock` (live commit-hash catches HEAD moving to an old-dated commit a timestamp compare would miss); REMOTE (default, `federation_health` on the HTTP MCP path) → `lagFromContentMs(row.newest_content_at, ...)`, NO git subprocess (trust boundary). `commitTimeMs(localPath, sha)` is the `newestCommitMs` sibling pinned to an arbitrary commit (committer time via `git show -s --format=%ct <sha>`, fail-open null, execFileSync array args) — the resumable sync stamps `newest_content_at` against its pinned target commit, not whatever HEAD raced to. Pinned by `test/source-health.test.ts`.
+- `src/core/npm-squat-check.ts` — classifies `gbrain` PATH entries as real, foreign npm package, broken, or unknown for doctor's `npm_squat` check. On Windows it normalizes Git Bash/MSYS drive paths (`/c/...` → `C:/...`) and tries the native `.exe` suffix before reporting a broken entry; non-Windows classification keeps the original single-candidate behavior. Pinned by `test/npm-squat-check.test.ts`.
 - `src/core/git-remote.ts` — SSRF-hardened git invocations for remote-source `cloneRepo`, `pullRepo`, and `fetchRemote(repoPath, branch)` (the last added for the sync cost-estimator's fetch-first path, #2139, so a cost preview / dry-run fetches through the same hardened flags + `GIT_TERMINAL_PROMPT=0` as real sync rather than a less-protected route). Exports two distinct flag constants because `git`'s argv grammar treats them differently: `GIT_SSRF_FLAGS` (3 `-c` config flags — `protocol.allow=user`, `protocol.file.allow=never`, `http.allowRedirects=false`) is global config, spread BEFORE the subcommand verb; `GIT_SSRF_SUBCOMMAND_FLAGS = ['--no-recurse-submodules']` is subcommand-scoped, spread AFTER the verb (a combined array would spread `--no-recurse-submodules` before the verb where real git rejects it exit 129). `cloneRepo` argv: `git <GIT_SSRF_FLAGS> clone <GIT_SSRF_SUBCOMMAND_FLAGS> --depth=1 [--branch X] -- <url> <dir>`. `pullRepo` argv: `git <GIT_SSRF_FLAGS> -C <dir> pull <GIT_SSRF_SUBCOMMAND_FLAGS> --ff-only`. Pinned by `test/git-remote.test.ts` position-anchored regression guard (`argv.indexOf('--no-recurse-submodules') > argv.indexOf(verb)`). Also exports the durability-side helpers that power `gbrain sources harden/pull`: `GIT_ENV_AUTH` (the no-prompt env minus the askpass `/bin/false` overrides, so an auth'd push/fetch can consult the repo's configured credential helper while `GIT_TERMINAL_PROMPT=0` still fails fast on a missing credential), `divergenceSafePull(repoPath, branch)` (fetch + `pull --rebase`; returns `skipped_dirty` on a dirty tree, `conflict_aborted` on a rebase conflict after `rebase --abort` so the tree is never left mid-rebase, else `up_to_date`/`advanced`), `detectDefaultBranch` (origin/HEAD → current branch → `main`), `pushProbe(repoPath, branch)` (authenticated `push --dry-run` that proves push access and classifies `auth`/`protected`/`unreachable`), and `isWorkingTreeDirty`. These auth'd paths route their `protocol.file.allow` through `GBRAIN_GIT_ALLOW_FILE_TRANSPORT` (default `never`; set `=1` for self-hosted filesystem remotes), unlike clone/pull which stay strict.
 - `src/core/brain-repo-durability.ts` + `src/commands/sources-harden.ts` — brain-repo git durability. `hardenBrainRepo(opts)` makes a brain's working tree durable, idempotently: divergence-safe pull, a LOCAL untracked `.git/hooks/post-commit` auto-push safety net (never committed — a pulled commit can't rewrite executed code next to the token; installed into the active `core.hooksPath` dir and excluded via `.git/info/exclude` when that dir is tracked), a committed `scripts/brain-commit-push.sh` that refuses to exit 0 without a confirmed push and stages+commits BEFORE any pull so a dirty tree of modified pages (the write-through shape) can still be committed — the push-retry's rebase-on-reject handles a remote that advanced (#2426; hook + helper render from ONE bash push-retry template — DRY at the TS source, not by the hook sourcing a repo-controlled script), durability rules patched into the active resolver file (`findResolverFile` → RESOLVER.md > AGENTS.md; taxonomy rendered from the bundled `_brain-filing-rules.json`), a minimal DB-free pull cron (launchd/crontab running `gbrain sources pull --path <dir>` so it never opens the PGLite single-writer lock), and a push-probe verify (no heartbeat commit). Credential is REPO-scoped (`acceptPat` from `--pat-file`/`GBRAIN_GITHUB_PAT`, warns on loose perms; reuses an existing repo-local `credential.helper`, else a `0600` store wired via repo-local config); the token is redacted everywhere via `redactSecretsInText` and never enters the repo, remote URL, logs, or `DurabilityReport`. `unhardenBrainRepo` removes the cron/hook/credential wiring (ownership-fingerprinted) and runs before `sources remove`. CLI: `gbrain sources harden <id|--all>` / `pull <id>|--path <dir>` / `unharden <id>`; auto-harden fires on `sources add --url ... --pat-file` for managed clones (`--no-harden` opts out). `sources pull --path` is dispatched in `src/cli.ts` BEFORE `connectEngine` so the cron stays DB-free. CLI-only (writes executables + an OS cron + a credential helper on the host); never exposed over MCP. Tests: `test/brain-repo-durability.serial.test.ts`, `test/git-remote-durable.serial.test.ts`, `test/brain-durability-hook.serial.test.ts`, `test/durability-cron.test.ts`.
 - `src/commands/storage.ts` — `gbrain storage status [--repo P] [--json]`. Split into pure data (`getStorageStatus`) + JSON formatter + human formatter (ASCII-only) matching the `orphans.ts` pattern. `PageCountsByTier` and `DiskUsageByTier` are distinct nominal types so swaps fail at compile time.