This commit introduces a substantial security and runtime architecture update for host mode, with three major goals: (1) enforce OS-level sandboxing by default, (2) support a controlled temporary direct-execution escape hatch for admin users, and (3) eliminate silent fallback behavior that could hide risk.
Backend/runtime changes:\n- Added a unified host sandbox runner (macOS sandbox-exec / Linux bubblewrap+seccomp / Windows WSL2).\n- Converted host terminal creation to sandboxed interactive shells by default.\n- Kept run_command/run_python on the same execution policy and added host execution mode plumbing (sandbox|direct).\n- Added session-scoped direct mode with TTL auto-revert (default 10 minutes), configurable via environment.\n- Added execution mode APIs (GET/POST /api/execution-mode), host+admin gating, status propagation, and rate limiting.\n- Added runtime refresh hooks so tool calls honor TTL expiration and mode transitions consistently.\n- Removed docker->host silent fallback paths: docker startup/runtime failures now fail fast instead of degrading silently.\n- Added host sandbox prompt injection (host-only) to guide agent behavior under permission constraints.
Configuration and policy changes:\n- Added HOST_EXECUTION_MODE_DEFAULT and HOST_EXECUTION_DIRECT_TTL_SECONDS.\n- Added HOST_SANDBOX_MACOS_WRITABLE_PATHS to support user-defined writable path allowlists.\n- Updated macOS sandbox profile generation to use minimal defaults (workspace + tmp + /dev/null) plus explicit allowlist extensions.\n- Updated .env.example documentation for new execution/sandbox controls.
Frontend changes:\n- Extended permission popover to a two-column model (Permission + Execution Environment) for host admin sessions.\n- Added execution mode state/options to app state, fetching, and status synchronization flows.\n- Added execution mode switching action and user feedback toasts.\n- Kept warning emphasis via text styling only (removed warning border per UX request).
Validation:\n- Python syntax checks passed for modified backend modules.\n- Existing smoke tests passed: python3 -m unittest test.test_server_refactor_smoke\n- Frontend production build passed: npm run build
