Add GOVERNANCE_DENIED error code to protocol

[bokelley]

Context

The protocol has COMPLIANCE_UNSATISFIED as a generic compliance error, but no specific code for governance denial. When a seller calls check_governance and the governance agent denies, the seller needs to return an error to the buyer — and the buyer needs to know it was specifically a governance denial, not a content standards failure or brand safety issue.

Proposal

Add GOVERNANCE_DENIED to the standard error codes table:

Code	Recovery	Description
GOVERNANCE_DENIED	correctable	A registered governance agent denied the transaction. The buyer may restructure the buy, escalate to a human, or contact the governance agent.

Recovery is correctable because the buyer can take action — reduce the budget, split into smaller transactions, escalate to human authority, or change the plan.

Why not COMPLIANCE_UNSATISFIED?

COMPLIANCE_UNSATISFIED is too generic. A buyer receiving it doesn't know whether:

• Governance denied the buy (action: escalate or restructure)
• Content standards failed (action: fix the creative)
• Brand safety was violated (action: change targeting)

Each requires a different buyer response. Governance denial is a distinct workflow — the buyer may need to escalate to human spending authority or restructure into smaller transactions within the governance plan's limits.

Where to update

• Error codes table in the protocol spec
• src/lib/types/error-codes.ts in adcp-client (or wherever standard codes are defined)
• docs/llms.txt error codes section
• Training agent's create_media_buy handler should return GOVERNANCE_DENIED instead of / in addition to COMPLIANCE_UNSATISFIED

Related

• feat: composable scenario library for seller storyboards adcp-client#528 — scenario library with governance scenarios (currently validates GOVERNANCE_DENIED)
• feat: createAdcpServer with domain-grouped handlers and governance helper adcp-client#541 — createAdcpServer with governanceDeniedError() helper (currently uses COMPLIANCE_UNSATISFIED)