Enforce headless decisions with a versioned migration contract #23

Goal

Make headless runs fail closed when a decision is missing (no foreign writes), using an approved, explicit migration and compatibility contract; any intentional breaking change requires a versioned schema and SemVer review.

Observations

• A newly required intent conflicts with absolute CLI backward compatibility.
• Any intentional break needs an approved versioned schema, migration, and SemVer decision; a breaking release has not yet been selected.
• Old syntax must not be preserved by bypassing the new gate.

Decision gate

Approve the schema, compatibility, migration, and SemVer plan before implementing any intentional break.

Acceptance criteria

• A missing headless decision performs no writes to foreign resources.
• Any intentional break ships only with an approved versioned schema, migration, and SemVer decision.
• The CLI does not preserve old syntax by bypassing the new gate.
• The failure is explicit with a non-zero exit and a clear reason.

Verification

• Headless run without a decision -> non-zero exit, zero writes.
• Schema migration fixture -> the old plan migrates under the approved version, not by bypass.

Release checkpoint

Remaining risk: any chosen break must be communicated with the reviewed version change.

Tracking

Roadmap item: B04-02. All acceptance criteria remain pending; publication does not grant approval or release authority.

Dependencies

• Depends on Design enforceable per-module reconciliation intent artifacts #22 (B04-01).