[Track] Control-plane profile boundary and unsafe transition enforcement

[SMC17]

Goal

Keep production profile as a hard boundary for autonomous operations.

Deliverables

• Maintain strict method allowlist/denylist behavior in production profile.
• Expand deterministic policy error contracts for boundary violations.
• Add/maintain tests for unsafe profile transitions and invariant violations.

Acceptance

• src/rpc_methods.zig and src/rpc.zig tests cover boundary and transitions.
• Gate C enforces policy fixtures (submit_blocked_in_production and follow-ons).
• docs/CONTROL_PLANE_POLICY.md remains in sync with implementation.

Linked Epic

• [Vision Epic] Agent-native XRP Ledger daemon in Zig: execution program #4

[SMC17]

Child delivery queue: #13 (good first issue), #14 (expert-only). Suggested order: #13 -> #14.

[SMC17]

New child issues for this track: #29 (production allowlist positive-case Gate C coverage), #30 (policy snapshot artifact drift detection).