fix: relaunch chat in a fresh process when setup leaves stdin dirty

[who96]

Summary

• Fixes [Setup]: OSError: [Errno 22] Invalid argument:[prompt_toolkit crash] #5884
• catch OSError with errno == 22 in hermes_cli/setup.py::_offer_launch_chat()
• fall back to os.execvp(...) so hermes chat starts in a fresh process with clean stdio state
• add regression tests for the fallback path and for re-raising unrelated OSErrors

What did NOT change

• the normal in-process cmd_chat(...) path still runs when chat starts cleanly
• no chat flags, provider selection behavior, or setup flow prompts were changed

User-visible changes

• after setup finishes, choosing Launch hermes chat now? no longer crashes on the known stdin-selector failure path
• when the selector registration bug is hit, Hermes prints Starting chat in a fresh session... and relaunches chat

Compatibility / Security impact

• no API, config schema, or database changes
• no new permissions or network behavior
• behavior change is limited to the setup-to-chat handoff when the known OSError(22, ...) path is hit

Test plan

• pytest tests/hermes_cli/test_setup.py -k offer_launch_chat_reexecs_after_oserror -q
• pytest tests/hermes_cli/test_setup.py -k offer_launch_chat_reraises_unrelated_oserror -q
• pytest tests/hermes_cli/test_setup.py -k 'binary_missing or binary_exec_fails' -q
• pytest tests/hermes_cli/test_setup.py -q
• pytest tests/ -v

Evidence / Actual results

• targeted setup suite: 14 passed in 2.02s
• focused fallback tests: 4 passed in 1.35s
• full suite on this branch: 28 failed, 9355 passed, 31 skipped, 1 xpassed
• full suite on clean origin/main baseline: 28 failed, 9351 passed, 31 skipped, 1 xpassed
• real TTY smoke test in isolated temp profile: setup wizard reached Launch hermes chat now?, accepted y, and launched chat TUI without the selector crash
• verification profile path: /tmp/hermes-pr1-hv.XOBmql

Human verification

Completed in a real TTY against an isolated temp profile:

• HERMES_HOME=/tmp/hermes-pr1-hv.XOBmql
• ran hermes setup in the temp venv
• skipped the OpenClaw import prompt to avoid using existing user state
• reached Launch hermes chat now?
• answered y
• Hermes launched the chat TUI and showed Welcome to Hermes Agent! Type your message or /help for commands.

What was verified:

• the setup-to-chat handoff completes in a fresh session
• the selector/stdin crash does not occur on the launch path

What was not verified:

• sending a chat message through a live provider in this temp profile
• provider-auth setup was not completed in the isolated run

Risks / rollback

• risk is limited to the setup handoff path; unrelated OSErrors are re-raised instead of triggering a relaunch
• rollback is a simple revert of hermes_cli/setup.py and tests/hermes_cli/test_setup.py

[teknium1]

Closing as stale — the code path this addresses no longer exists on main.

Triage notes (high confidence):
PR patches _offer_launch_chat() in hermes_cli/setup.py, but that function no longer exists on origin/main (git grep '_offer_launch_chat|Launch hermes chat|offer_launch' returns no hits) — surrounding code was restructured.

If this PR's intent is still relevant against the current code, please rebase or open a fresh PR.

(Bulk-closed during a CLI PR triage sweep.)