Status: ready-for-agent

# 07 — FRAUD: On-demand commitment + hop bisection blame

## What to build

On audit selection, require nodes to supply TOPLOC-style fingerprints of **output boundary activations** per hop (on-demand, brief retention). On verify failure, referee identifies the **first divergent hop** — not always the last text node.

**Code refs:**

- `packages/validator/meshnet_validator/__init__.py` — `_slash_route`, `_final_text_node` bug (~102–140) — blames `max(shard_end)` only
- `packages/tracker/meshnet_tracker/server.py` — route hop construction (~1774–1783) — cut-points for bisection
- Research: `.scratch/alpha-hardening/research-verifiable-inference.md` §1.2, §8 layer 3 (Verde **pattern**, not on-chain game)

## Test-first

1. Red: two-hop route, corrupt hop-0 activations — `_final_text_node` blames hop-1 — test must fail.
2. Green: bisection selects hop-0; forfeit targets hop-0 wallet.
3. On-demand: commitment requested only when audit flag set on proxied request.

## Acceptance criteria

- [ ] Audit requests carry tracker RNG/VRF flag indistinguishable from normal traffic (research §6)
- [ ] Nodes retain recent boundary activations for on-demand commit window (configurable TTL)
- [ ] Validator/tracker compares fingerprints at each hop cut-point; first mismatch = culprit
- [ ] `_final_text_node` removed or limited to text-only fallback
- [ ] Integration test: multi-hop pipeline, fault injected at known hop

## ADR links

- [ADR-0018](../../docs/adr/0018-fraud-detection-verification-and-reputation.md) §3–4

## Blocked by

- `06-fraud-toploc-integration.md`