shadow-verify

## Sub-agent contract /contract When a sub-agent (or wave) returns investigation findings, code-review conclusions, audit claims, refactor plans, or counts that will drive user decisions or file changes, do NOT surface the report. Instead, run a shadow verification wave **before** merging. **Wave 2 — Adversarial verifiers (parallel, independent):** 1. Extract 2–3 concrete, re-checkable claims from the returned report (e.g., "X function is unused", "file Y exceeds 300 lines", "PR targets main", "no tests cover Z"). 2. Dispatch one shadow sub-agent per claim, in parallel. Each receives ONLY the claim + the user's original goal — never the original agent's reasoning or cited evidence. **Default to `subagent_type: "research-agent"` (mechanically locked to Read/Grep/Glob/WebFetch/WebSearch — cannot Edit/commit/push).** If the claim requires Bash to verify (running a failing test, `gh pr view`, `git log origin/...`), fall back to a Bash-capable subagent type with `isolation: "worktree"` and prepend this prefix to the prompt: *"Verifier sub-agent — do not Edit, Write, commit, push, `gh pr create`, or `curl`. Return findings only."* 3. Each verifier re-derives the verdict independently using tool calls only — never re-reading the original report's reasoning. Returns `{claim, verifier_verdict, evidence_pointer, evidence_base}`, where `verifier_verdict` is one of `CONFIRMED`, `REFUTED`, or `UNVERIFIABLE`, and `evidence_base` is `independent-rederivation` (read primary sources *outsid...