UVO Action Gate: deterministic validation of an agent action proposal across up to nine stages, fail-fast. Returns APPROVE/WARN/ESCALATE/BLOCK.

Deterministic pre-flight validation for an autonomous agent action. Up to nine validation stages (IDs L0-L6, L8, L9 - historically non-contiguous; there is no L7) covering schema, measurability, reversibility, containment, danger, citation, commitment, existence and hallucination. Execution is fail-fast: a blocking stage ends the run, so not every request executes all nine stages. Stage L1 (hallucination) is reported but runs disabled unless enabled by the caller; this route does not enable it - use /v2/uvo_academic_verify for academic claim verification. Returns decision (APPROVE/WARN/ESCALATE/BLOCK), risk_score, blocking_layer and a per-stage layers array. Input contract: the body is {proposal: {...}}. Inside the proposal, claim and expected_outcome are required strings of at least 10 characters; success_metric is required for a non-BLOCK verdict (stage L6 blocks a proposal without it); action_type is optional but, when present, must be exactly one of shell, http, code_diff, decision, filesystem, config_change (lower case). Unknown fields are accepted. Sub-100ms validation time; transport not included.