Orchestrator dispatches read-only reviewer without asserting worktree HEAD == review SHA

## Process-gap

When the orchestrator dispatches a read-only reviewer agent (adversary, consistency-validator, pr-reviewer) to review an integrated branch state at a specific SHA, there is no enforced pre-dispatch step that (a) fast-forward-pulls the working tree and (b) asserts `git rev-parse HEAD` equals the intended review SHA before the reviewer runs.

Read-only agents cannot (and should not) perform checkout. If the working tree is stale relative to the SHA the orchestrator believes it is reviewing, the reviewer can emit false "code absent / not implemented" findings against code that is actually present at the intended SHA. This is the same failure class the worktree-identity preflight (issues #169/#176) mitigates on the reviewer side — but the reviewer-side assertion only detects the mismatch; it cannot fix it.

## Proposed mitigation

Codify an orchestrator-side discipline (in the orchestrator skill / per-story + wave convergence workflow): BEFORE dispatching any read-only reviewer against an integrated SHA, dispatch a write-capable agent (devops-engineer) to `git fetch && git pull --ff-only` and assert HEAD == the intended review SHA. Only on a clean PASS proceed to the read-only reviewer dispatch. Never delegate checkout/sync to a read-only agent.

## Severity
Medium — produces false-negative review findings that waste a full review cycle and can mask real convergence.