mcpx daemons: dead records listed forever, custom-state daemons missed, paths.config file entry silently ignored #278

Summary

mcpx daemons promises "every daemon on this machine" (internal/cli/manual.go), but daemon discovery in this repo's pkgs/mcpx copy has three defects. All three were found and fixed in dezren39/darwin-nix#369 (PR dezren39/darwin-nix#381); the fix was never ported to this copy. The pre-fix files here are byte-identical to dezren39/nix's pre-fix versions (verified: internal/daemon/paths.go, paths_test.go, server.go, internal/cli/manual.go, internal/settings/consumed_test.go, docs/parity.md; commands.go/root.go differ only by this repo's already-ported #265/#274/#276 fixes, in unrelated hunks).

Defects (verified on main 584d869)

1. Dead daemons are listed forever. Paths.ListDaemons (internal/daemon/paths.go:229) returns every daemon*.json record in the state dir with no liveness check, and nothing ever removes a record whose daemon was killed or crashed (a clean exit removes its own record at server.go:488/1158; a killed one cannot). Reproduced with a binary built from main: a record with a dead PID is listed by mcpx daemons as RUNNING false, and the record file is still on disk after repeated listings. stop --all iterates the same stale records.

2. Daemons with their own state directory are invisible. A daemon started with a custom state dir (paths.state in config, --paths-state, or MCPX_STATE_DIR) writes its record only there (WriteInfo, paths.go:284). ListDaemons scans only the caller's own state dir, so a normal mcpx daemons / stop --all never sees it. Reproduced: a live record placed only in a second state dir is listed from that dir but not from the first.

3. A paths.config entry naming a file is silently ignored. The entries are directories searched for config files; pointing one at a file (a natural reading of the setting) silently loads the default config instead. adoptSettings (internal/cli/root.go:195) never inspects the entries, and internal/settings/consumed_test.go keeps paths.config on the unread-allowlist as "circular by construction".

Suggested fix (mirror dezren39/nix PR #381)

• Paths.PruneStale(): remove records whose PID is gone (signal-0 liveness, EPERM = alive; pid-less records kept); mcpx daemons and stop --all prune before listing.
• Mirror records: WriteInfo also publishes the record into the default state dir (keyed name, best-effort) when the daemon's state dir is custom; new RemoveInfo() removes primary + mirror and replaces the two os.Remove(s.paths.Info) calls in server.go. Listings search the caller's dir + the default dir, deduped by socket.
• adoptSettings warns once when a paths.config entry names a file, naming --config/MCPX_CONFIG as the way to pick a file; paths.config leaves the consumed-test allowlist.
• Update the daemons entry in internal/cli/manual.go and regenerate docs/parity.md.

Acceptance criteria

• A daemon record with a dead PID no longer appears in mcpx daemons output and its file is removed; records with a live PID or no PID are untouched.
• A daemon started in a custom state dir appears in a default-state-dir mcpx daemons listing (and stop --all reaches it), exactly once.
• A paths.config entry naming a file produces one stderr warning naming --config/MCPX_CONFIG; directory entries stay silent.
• New daemon tests cover ProcessAlive/PruneStale/mirroring; go test ./internal/daemon/ ./internal/settings/ ./internal/cli/ passes.