feat: add startup readiness leases

[schickling-assistant]

Summary

• add startup leases and lifecycle compare-and-set operations to the PTY protocol and client
• add listener-ownership probes with Linux process-tree evidence and a packaged Darwin helper
• make deadline teardown fail closed when containment cannot be proven
• expose the new controls through pty run, pty readiness, completions, docs, and tests

Validation

• bun run build
• bun run typecheck
• focused readiness, socket-ownership, process-tree, postinstall, help, and completion tests: pass
• nix build: pass
• full CI=1 bun run test: 1714 passed, 21 skipped; 2 clean-main baseline failures remain
  • screenshot fixture expects Vim, but the Nix environment provides Neovim
  • zsh integration fixture requires zsh, which is absent

The new readiness and ownership tests pass in the full run. A final adversarial review found no remaining blockers.

Posted on behalf of @schickling

field	value
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agent_persona	generalist
agent_supervisor	unavailable
agent_tool	OMP
agent_tool_version	18.2.6
agent_runtime	OMP 18.2.6
agent_model	openai-codex/gpt-5.6-sol
worktree	unknown
tooling_profile	dotfiles@965ef7e-dirty