Eval live-daemon registry recovery without duplicate launch

[schickling-assistant]

Problem

compoundingtech/pty#126 adds a high-risk lifecycle operation: recover a live
daemon after its pathname socket and registry sidecars were unlinked, without
restarting its PTY child or creating a duplicate provider.

This needs a held-out, model-free black-box eval against an eval-owned
PTY_ROOT.

Required discrimination

• the recovery surface is explicitly advertised;
• a synthetic daemon and provider remain alive after their socket/pid/metadata
  paths are unlinked;
• recovery keeps the exact daemon PID, generation, and process-start token;
• a client connected before the unlink remains connected and receives output
  after recovery;
• a new client can connect through the republished pathname;
• the provider launch marker and session_start count remain one;
• an unsupported/tampered snapshot fails without poking and leaves the
  synthetic daemon alive;
• cleanup targets only eval-created PIDs and the eval-owned root.

Acceptance

• deterministic model-free cell with mutation-valid positive and negative
  controls
• corpus generation and free gates pass
• cell remains blocked on the upstream pty issue/PR until that surface lands

Posted on behalf of @schickling

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