Plan: Socket startup preservation

Keep the correction in signaltty-server::server::serve, the boundary that owns socket inspection and removal. Inspect with symlink_metadata and the Unix file type before connecting. Refuse non-socket entries, report inspection errors, and unlink only after a refused connection.

Use the existing server test context for fast failing startup tests, including file bytes and an inaccessible live listener's inode. Add symbolic-link and live-listener refusals, then a real IPC recovery test for an abandoned socket. Run targeted tests before and after the fix, followed by scripts/verify.sh full.

The constitution is satisfied by a recorded specification, test-first changes, the existing production seam, and the full verification gate. This repairs the existing startup policy; it adds no architecture or protocol decision.