Connection-class infrastructure failures on remote terminal backends (SSH
host unreachable/timed out, Docker daemon down or missing, remote file
sync failing on a dead link) previously surfaced to the model as raised
RuntimeError tracebacks. The model got a stack blob with no guidance and
the failure was indistinguishable from a tool bug.
Now:
- New EnvironmentConnectionError(RuntimeError) in tools/environments/base.py
carrying a reason + retry_hint. Subclassing RuntimeError keeps every
existing catcher working.
- ssh.py classifies connect-refused, connect-timeout, scp, remote mkdir,
bulk upload/download, and remote rm failures as connection errors.
- docker.py classifies all four _ensure_docker_available() failure paths
(missing exe, non-executable exe, daemon timeout, `docker version`
failure).
- terminal_tool catches EnvironmentConnectionError and returns a
structured tool result the model can act on:
{"status": "degraded", "reason": ..., "retry_hint": ..., "exit_code": -1}
The failed backend is evicted from the environment cache so a later
call retries from scratch — recovery is automatic once the backend is
reachable again.
- Config gate terminal.degraded_mode: warn|fail (default warn) in
config.yaml, bridged as TERMINAL_DEGRADED_MODE across all four bridge
sites (cli.py env_mappings, gateway/run.py _terminal_env_map,
TERMINAL_CONFIG_ENV_MAP, DEFAULT_CONFIG). "fail" preserves the
historical error+traceback tool result.
- Command failures (nonzero exit, command-not-found) are NOT touched —
only infrastructure failures classify as degraded.
Tests: tests/tools/test_terminal_degraded_mode.py (15 tests) covering
exception classification for ssh+docker, structured degraded results,
no-caching of degraded envs, recovery after the backend returns,
nonzero-exit results unaffected, fail-mode preservation, invalid-mode
fallback to warn, and the four-site config bridge invariant.
Inspired by: Claude Cowork degraded-backend behavior (idea-level,
docs-only evidence).
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