Observed Signal · Jun 26, 2026 · Technical Postmortem · Source: DEV Community · Impact: 2/5 · Sentiment: Neutral
--cap-drop ALL Broke the Gate Socket
A hardened AI-agent sandbox failed to record any governance decisions because container privileges and Unix-socket file modes interacted unexpectedly. Docker containers launched with --cap-drop ALL lose CAP_DAC_OVERRIDE, so an in-container uid 0 process is subject to normal discretionary access checks. The AGP daemon's AF_UNIX gate socket had mode 0775 (no write for "others"), and connect() to a Unix domain socket requires the write bit; the kernel returned EACCES and no tool calls reached the gate. CI dogfood surfaced the problem because a zero-decision journal marks the build red. The team fixed it by chmodding the host socket to 0777 before launching the sandbox (implemented in BunClaudeProcess), added a unit test asserting world-connectable mode in docker mode, and retained the --cap-drop ALL posture rather than re-granting CAP_DAC_OVERRIDE.
Operational infrastructure bug with moderate relevance to teams running AI agents in hardened containers; demonstrates a non-obvious interaction between Linux capabilities and Unix-socket permissions and supplies a reproducible fix and test.
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Key Takeaways & Evidence Grounding
- --cap-drop ALL in Docker removes CAP_DAC_OVERRIDE, causing root inside the container to lose permission-bypass capabilities.
- Connecting to an AF_UNIX pathname requires write permission on the socket file; the gate socket was mode 0775, leaving 'others' without write.
- connect() failed with EACCES in the container, so zero tool calls reached the agent-governance-plane (AGP) gate and the CI journal showed no decisions.
- Fix: BunClaudeProcess chmods the gate socket to 0777 before launching the sandbox; a test now asserts the socket is world-connectable in docker mode.
Connected Companies & Entities
1 Entity mapped“The article describes running the sandbox with Docker flags: "docker run --cap-drop ALL --network none --read-only -v \"$GATE_SOCK:$GATE_SOC...”
Ontology Mapping & Concepts
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