[nhuelstng]

Issue: Closes #435

What

• New omac start --skip-unregistered: starts despite unregistered skills, with a warning naming them.
• Skipped skills run without sidecar, secrets or install script, and are not registered.
• Each skipped skill is written to the audit log (route.state, skipped-unregistered).

Why

Today the only ways past the refusal are registering the skill or deleting it (see #435).

How

• internal/cli/start.go: the existing refusal is bypassed only when the flag is set; the audit events are emitted after session.start.
• Safety rests on existing behaviour: only registered skills get a sidecar, and unapproved skill folders are hidden by the built-in sandbox (fix(skills): hide skill dirs whose SKILL.md is not host-approved #395). On other backends the existing notice says the skill stays visible, and the new warning says so too.

Verification

• go build ./...: ok
• go test ./internal/cli/ ./internal/audit/: ok
• New tests: flag parsing; start succeeds with warning; skill stays unregistered; audit log has the record.
• Not run: a real sandboxed omac start against a skill dir (the hiding relies on fix(skills): hide skill dirs whose SKILL.md is not host-approved #395's tests).

Follow-up

None planned.

🤖 Generated with Claude Code

[nhuelstng]

Verification update: ran the built binary against a real workdir on Linux (bwrap) with an unregistered skill app-probe (HOME and XDG dirs isolated).

• Without the flag: refused, exit 4, inner command did not run.
• With --skip-unregistered: warning printed, session started, inner command ran.
• Inside the sandbox .opencode/skills/app-probe/ was an empty mask: cat .../SKILL.md failed with "No such file or directory". omac printed "Hidden from this session" for the skill.
• No sidecar was started and the skill was not registered.
• Audit log contained {"type":"route.state","skill":"app-probe","state":"skipped-unregistered",...}.

Not covered: macOS, non-native sandbox backends, --no-sandbox.