Agent fleets are getting good at talking to each other over A2A — and bad at trusting what they say. Sentinel Mesh sits in the message path: every claim a worker emits is judged by a 3-lens adversarial Gemini panel against memory as ground truth, money/auth claims hit a deterministic tripwire with no model in the loop, and what survives is written back as verified memory — so the fleet gets cheaper and more reliable every run.
Three moving parts, one compounding loop. A claim flagged and corrected on Run 1 is auto-vetoed on Run 2; a claim already verified never reaches a model again.
The sentinel binds to ADK's non-experimental before_tool_callback on a real A2A fleet
(to_a2a() workers, RemoteA2aAgent orchestrator). A vetoed claim's tool never fires.
A 3-lens adversarial Gemini panel on Vertex (robust · overreach · nevers) rules in parallel; a deterministic regex tripwire independently hard-vetoes money / auth / destructive claims before any model can rationalize them.
Accepts are written back into a provenance-tracked verified ledger — its own file, so broker refresh jobs can never clobber rulings. Run N+1 reads strictly cleaner memory.
One hallucinated claim, remembered once, contaminates every downstream agent — and a fleet sharing memory over A2A shares the contamination. Sentinel Mesh is the third category: not observability (watch it fail), not per-action guardrails (block, learn nothing) — verified memory as infrastructure.
[ADVISORY] memory (curated, unadjudicated) caps suspicion at a flag; only [VERIFIED] rows that survived the panel justify a hard veto.
"December 31" and "31 December" agree. The rubric scores meaning, not string distance — so honest restatement is never punished as a lie.
Money / auth / destructive claims hit a regex word-boundary gate and are vetoed before a model is even asked — the one place you cannot afford a confident hallucination.
A fleet exports an HMAC-signed Trust Passport; a second fleet imports it and vetoes a lie it has never seen — re-serving the inherited fact at 0 calls. A control fleet without it only flags the same lie.