fix(sandbox): distinguish descriptor lookup outcomes

[johntmyers]

Summary

Distinguish verified unregistered descriptors from descriptor inspection failures in the sandbox network broker. Deny operations when the broker cannot verify the descriptor before a native fallback.

Related Issue

No issue, per direct request.

Changes

• Preserve distinct procfs lookup outcomes for sockets, non-sockets, and inspection errors.
• Apply fail-closed handling to connect, bind, listen, and send fallback paths.
• Add regression coverage for an unreadable workload and native Unix socket behavior.

Testing

• Linux sandbox compile and Clippy checks pass
• Non-root Linux regression tests pass
• Docker end-to-end run passes, including transparent_tcp
• Repository commit hooks pass

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (not applicable)

[github-actions]

Label test:e2e applied for 9231102. Open the existing run and click Re-run all jobs to execute with the label set. The run will execute the standard E2E suite after building the required gateway, sandbox, and supervisor images once. The matching required CI gate status on this PR will flip green automatically once the run finishes.

[johntmyers]

gator-agent

PR Review Status

The independent review found no blocking problems in the descriptor-inspection change. Lookup errors now deny native fallback, while verified unregistered descriptors retain native Unix socket behavior.

Blocking findings: None.
Carried findings: None.
Non-blocking suggestions: None.

Gator metadata

• Validation: Focused sandbox network enforcement fix from a verified maintainer.
• Docs: No published interface or configuration change; existing support documentation requires broker task visibility and fail-closed qualification.
• Head SHA: 92311026f6f0261d1b716519dc6f16d720fee168
• Base SHA: 0d4d22eab316148e500716f86280457e9e840023
• Merge base SHA: 0d4d22eab316148e500716f86280457e9e840023
• Patch ID: c0d68130e9f92ee6b235b9327f11f33e6fd84a19
• Gator payload: 12
• Review mode: initial
• Previous reviewed SHA: none
• Review budget exhausted: no
• Maintainer decision required: no
• Checks: DCO, vouch, Helm Lint, and Trivy Changes passed. Branch Checks attempt 2 is running; the earlier macOS failure occurred in Rust setup before the build.
• E2E: test:e2e applied. The mirror matches the current head. Following E2E Label Help, run 38438104172 was rerun and confirmed queued; test results are pending.
• Next state: gator:watch-pipeline

[drew]

A closed file descriptor should retain the syscall's EBADF behavior.

[johntmyers]

gator-agent

PR Review Status

Thanks @drew, I checked your request to preserve EBADF for closed descriptors. The latest commit maps a confirmed missing descriptor to EBADF, while missing tasks and other inspection errors remain distinct and fail closed. The independent follow-up review found no blocking issues in the author-only delta; regression coverage exercises the lookup, both registry paths, and brokered listen.

Blocking findings: None.
Carried findings: None.

Gator metadata

• Validation: Focused sandbox network enforcement fix from a verified maintainer.
• Docs: No new published interface or configuration; this delta restores native closed-descriptor error behavior.
• Checks: Current-head Branch Checks are running; DCO, PR Issue Acceptance, Helm Lint, and Trivy Changes passed.
• E2E: test:e2e remains applied; current-head Branch E2E Checks is queued. The label-help rerun instruction concerned the previous head; the new head already has its own required run.
• Head SHA: 3e7bcebdf9533a5142b0afb3edda8a4d26a27bc7
• Base SHA: 0d4d22eab316148e500716f86280457e9e840023
• Merge base SHA: 0d4d22eab316148e500716f86280457e9e840023
• Patch ID: ba6f8717eeb7be0ebe5db6f9fa8d5a90a2d6ef4f
• Gator payload: 12
• Review mode: follow_up
• Previous reviewed SHA: 92311026f6f0261d1b716519dc6f16d720fee168
• Review budget exhausted: no
• Maintainer decision required: no
• Next state: gator:watch-pipeline