docs: add Shell Spawn Hard-Stop Rule for agent workflows (#258)
Documents fail-closed behavior when the shell executor fails to spawn
(exit_code: -1, empty stdout/stderr): probe once, mark shell unavailable,
hard-stop after two consecutive spawn failures, and emit a recovery report
(restart session, kill hung background terminals, prefer MCP-native paths)
instead of retry-spiralling.
- skills/llm-project-workflow/SKILL.md: portable rule section
- docs/llm-workflow-runbooks.md: Gitea runbook section
- gitea_mcp_server.py: shell_spawn_hard_stop operator guide rule
- tests/test_shell_spawn_hard_stop_docs.py: doc-contract tests (5)
- tests/test_operator_guide.py: require the new guide key
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>