[checkpoint] Restore GRL Tetris episodes #3238

Parent

Child of #3219 and #3024.

Problem and state owner

resources_servers/grl_tetris/app.py owns a live Tetris environment, board, active piece, counters, reward, observation, done state, and piece RNG.

Proposed adapter

Provide an explicit JSON codec and recreate a fresh environment without replaying batched actions.

Implement explicit checkpoint opt-in, route classification, export/restore/retire hooks, execution-to-session binding, revision reporting, atomic replacement under attempt N+1, and stale-attempt fencing.

Acceptance criteria

• Restore between batched turns preserves the active piece and makes the next action result identical; terminal cleanup removes the episode.
• Checkpoint after multiple mutations, replace the server process, restore, and compare the next operation with an uninterrupted execution.
• Corrupt or incomplete bulk state activates no sessions.
• Attempt N cannot mutate or retire restored attempt N+1.
• Terminal cleanup is idempotent and releases restored state exactly once.