feat(cli): add attach-only mode

[schickling-assistant]

Why

pty attach currently prompts to restart retained dead-session metadata. A
TTY-backed relay can remain at that prompt after its target dies, then consume
later input intended for the target as permission to execute the stored command.

Closes #122.

What

Add pty attach --no-restart <ref> as an explicit attach-only policy:

• running sessions attach normally;
• missing, exited, and vanished sessions exit nonzero without prompting;
• an attached client exits with the daemon and cannot start a second
  incarnation.

The existing interactive prompt and --auto-restart behavior remain unchanged.
Focused help, generated completion metadata, README usage, and the changelog
document the new flag.

How

The CLI now models attach restart behavior as a three-state policy:
prompt | always | never. The never branch refuses before entering the
dead-session presentation/restart path, so it does not display or execute
retained launch metadata. Contradictory --no-restart --auto-restart input is
rejected.

Rationale

This keeps the safety policy at the CLI boundary where the unsafe prompt exists,
while leaving the lower-level attach client and the existing interactive
contract intact.

Tests

• npm run typecheck
• npm run build
• npx vitest run tests/attach-no-restart.test.ts tests/help.test.ts tests/completions.test.ts tests/nesting-prevention.test.ts (57 passed)
• nix build .#pty --no-link
• Full local suite: 1,430 passed, 20 skipped, 4 environment-dependent failures
  in untouched shell/screenshot tests (zsh absent from the local Nix dev shell;
  local Vim resolves to Neovim and Vim/nano terminal-query screenshots time out).

The new regression suite covers missing, exited, vanished, running-then-exited,
delayed-input/no-second-incarnation, default interactive compatibility, and
--auto-restart compatibility.

Companion eval coverage: compoundingtech/evals#42.

Posted on behalf of @schickling

field	value
agent_name	co2-bear
agent_session_id	a078daee-6f98-4916-91a8-d21291407789
agent_tool	Codex CLI
agent_tool_version	0.145.0
agent_runtime	Codex CLI 0.145.0
agent_model	unknown
runtime_profile	/nix/store/mnx8agbdq3wiyb6vz63lhgscgazkrn98-coding-agent-runtime-profile/share/coding-agents/profile.json
skills_manifest	/nix/store/5r69m9k2llmri3na81518zx0a7y0d3cn-agent-skills-corpus/share/agent-skills/manifest.json
worktree	pty-attach-only/schickling-assistant/2026-07-30-attach-only
machine	dev3
tooling_profile	dotfiles@0fb7e03

[chatgpt-codex-connector]

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