fix(audit): preserve advisory content without feedback authority - #64

Summary

• Carry advisory metadata through the private gateway completion chain instead of losing it in a plain string.
• Permit consistent advisory research content without feedback writes or fallback model calls; retain normal ok feedback behavior.
• Reject failed/unknown/inconsistent status, invalid content and provider mismatch; preserve execute/direct-fallback policy and deterministic route/capital controls.
• Retain advisory status in public research results and plugin flattening; model JSON cannot override safety fields.

Validation

• Tests-first RED: 10 failed, 22 passed on unmodified production source.
• Final focused suite: 50 passed across AI audit and both plugin test files.
• Existing AAB client with synthetic HTTP: 4 cases passed. Parent independently reproduced both validations.
• Cleared environment, socket/subprocess denied, read-only existing libraries, fake feedback only.
• Ruff, diff, exact four-file scope and sensitive-pattern checks passed.

Boundaries

No provider/model/feedback/deployment/runtime call, dependency change or consumer pin rollout. Actual installed gateway-client source is unverified; this source patch does not imply runtime consumers are updated. Only private return shape changes; existing custom completion remains forbidden. PR/main triggers only offline CI.