feat(audit): network.loopback DENY audit channel#231
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Cross-platform run-audit channel: firma-core RunAuditEvent/RunAuditMessage, sidecar out-of-band ingest listener, and CLI wiring that binds the control socket when firma run provisions one. Also migrate two Windows-only allow(unsafe_code)/expect_used lints to expect(...) with reasons.
This was referenced Jul 6, 2026
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veeso
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## What Linux `bwrap` seccomp `user-notify` filter that traps the agent's `connect(2)` and **blocks** direct connections to any loopback address (`127.0.0.0/8`, `::1`, IPv4-mapped) except the proxy bridge and DNS stub ports, returning `EACCES`. Catches direct sockets that bypass `HTTP_PROXY`. Each block is reported to the Sidecar over the audit channel (PR #231) and recorded as a signed `DENY` / `network.loopback` / `loopback blocked` event, visible in `firma monitor`. Deny path is race-free; allow path uses `SECCOMP_USER_NOTIF_FLAG_CONTINUE`. Fails open with a warning if user-notify is unavailable — the private netns already isolates the agent, so the guard is defense-in-depth plus a direct-socket audit trail. ## Stack Based on #231 (audit channel). Part of the fir-383 split replacing #216.
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## What Documents the loopback egress enforcement model across backends: - `docs-site/src/content/docs/concepts/sandbox.md` — new **Loopback blocking** section (Linux seccomp guard, macOS sandbox-exec port-scope, proxy-only backends), updated network-boundary / proxy-bridge prose, and structural/invariant tables. - `crates/firma-run/src/backend/windows_wsl2.rs` — comment documenting the WSL2/Windows gap: the seccomp guard is Linux-host-only and not wired across the Windows->guest boundary; WSL2 stays proxy-only. `llms.txt` audit-channel + `network.loopback` action-class registry entries land in the branches that own them (#231 base; #232 linux; #233 macOS). ## Stack Based on #231 (audit channel, for the `network.loopback` model). Part of the fir-383 split replacing #216.
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What
Adds the firma run audit channel: an out-of-band control socket (
FIRMA_RUN_AUDIT_SOCK) carrying newline-delimitedfirma_core::RunAuditMessage. The Sidecar owns the mapping from eachRunAuditEventvariant to(action_class, decision, deny_reason, resource)and signs the result.RunAuditEvent::LoopbackBlockedis the first variant, mapping to the audit-onlynetwork.loopbackaction class (not inActionClassRegistry::v0_1, never Cedar-evaluated). The channel is reusable by future out-of-band producers rather than adding new sockets.Why
Foundation for the loopback egress guard (Linux) and future out-of-band enforcement facts to reach signed audit without touching the request pipeline.
Stack
Base of the fir-383 split. Replaces #216.