Why: PR #567 CI runs without a global Git user identity, causing every successful agent transport commit to fail with exit 128. Evidence: The focused no-identity regression plus AgentExecControllerTests and AgentExecHistoryTests pass (30 executions total); git diff --check passes. Impact: Supplies a deterministic non-secret identity only to git commit-tree; routing, receipts, and transport validation are unchanged. Refs: #567