mcpx: daemon discovery and mirroring ignore MCPX_STATE_DIR — env-default daemon missed by custom listings and its record leaks into the real default dir #305

Summary

mcpx daemon discovery and mirroring ignore MCPX_STATE_DIR in this repo's pkgs/mcpx copy — the same defect fixed in dezren39/nix as #407 (PR #410), never ported here.

ResolvePaths honours MCPX_STATE_DIR first (pkgs/mcpx/internal/daemon/paths.go:39), so the daemon a plain invocation talks to lives in the env-named directory. But the two places that need to know that treat only the XDG default as "default":

1. DaemonSearchDirs(primary) (paths.go:248) returns only [primary, DefaultStateDir()]. A listing (mcpx daemons, mcpx stop --all — internal/cli/commands.go:1553) whose own state came from a config file or --paths-state flag therefore never searches the env directory.
2. mirrorInfoPath() (paths.go:308) returns a mirror path for the env directory, because it only exempts p.State == DefaultStateDir(). The env-default daemon — e.g. a sandboxed daemon whose MCPX_STATE_DIR points inside a sandbox/temp tree — therefore mirrors its record into the real XDG default directory, where a non-sandboxed listing can see it and stop it. That is exactly the leak mirroring was supposed to avoid for default daemons.

Reproduction (verified on main 8fc1fb3)

Ported dezren39/nix PR #410's two regression tests to this copy, unmodified otherwise:

• TestDaemonSearchDirsIncludesTheEnvStateDir — FAIL: DaemonSearchDirs(custom) = [custom, <xdg>/mcpx], missing the MCPX_STATE_DIR directory entirely.
• TestWriteInfoDoesNotMirrorTheEnvDefaultDaemon — FAIL: env-default daemon leaked a mirror into the default dir: [{PID:… Socket:<envDir>/daemon.sock …}] — a Paths{State: def}.ListDaemons() in the XDG default returns the env daemon's record.

Both tests pass in dezren39/nix on the fixed code.

Why it matters

• Sandboxed / test daemons (the primary use of MCPX_STATE_DIR — see ResolvePaths' own comment: "for tests and sandboxes") leak into the user's real daemon listing and can be stopped by an unrelated non-sandboxed mcpx stop --all.
• Conversely, a custom-state listing can miss the machine's actual default (env) daemon, undermining the mcpx daemons "every daemon on the machine" promise established in mcpx daemons: dead records listed forever, custom-state daemons missed, paths.config file entry silently ignored #278.

Acceptance criteria

• DaemonSearchDirs also includes the MCPX_STATE_DIR directory (deduplicated; empty when unset).
• A daemon whose state directory is the MCPX_STATE_DIR directory does not mirror its record into the XDG default directory; a genuinely custom state directory still mirrors, env set or not.
• Regression tests equivalent to dezren39/nix PR fix(workflow): #407 trailing-fence drop strips a properly closed inner example's exemption in an unclosed draft #410's TestDaemonSearchDirsIncludesTheEnvStateDir and TestWriteInfoDoesNotMirrorTheEnvDefaultDaemon pass; the existing internal/daemon suite stays green.
• Suggested fix: port dezren39/nix PR fix(workflow): #407 trailing-fence drop strips a properly closed inner example's exemption in an unclosed draft #410 (envStateDir() helper in paths.go + the two tests) — the surrounding code in this copy is identical except issue-number comments (mcpx daemons: dead records listed forever, custom-state daemons missed, paths.config file entry silently ignored #278 here vs fix(mcpx): keep the daemon key stable when a config symlink is re-pointed (#368) #369 there).