Replace the checkpoint reason string bridge with generated-enum parity

[flyingrobots]

Classification

Contract/semantic-domain debt exposed by PR #282. Blocked by flyingrobots/echo#679.

Problem

Jim owns the checkpoint reason domain, but the transitional GraphQL contract currently declares reason: String!. The generated request model therefore accepts an arbitrary string, while native Jim separately defines the closed CheckpointReason enum and maintains handwritten string-to-enum and enum-to-string mappings.

The current native witnesses are intentionally fail-closed and prove the five accepted values. They do not give schema-to-native compile-time exhaustiveness: a future variant can drift across the authored schema, generated ABI, native enum, mapping functions, and tests.

Evidence

• GraphQL checkpoint input
• Jim-owned native checkpoint reason enum
• Handwritten generated/native reason bridge
• Closed-domain parity witness
• Why PR #282 retained the scalar

Why it matters

A checkpoint reason changes the meaning and identity of Jim's checkpoint proposition. Treating that domain as an open string in one layer makes semantic drift a runtime concern at an authority boundary.

Constraints

• Do not hand-edit generated artifacts.
• Jim continues to own checkpoint semantics.
• Echo continues to own admission, scheduling, receipts, ticks, WAL, and causal history.
• Invalid or unknown values must fail before admission.
• Keep this as compatibility work; Edict remains the intended native invocation path.

Acceptance criteria

• Fix or consume echo-wesley-gen emits uncompilable Rust for GraphQL enums echo#679 before changing the schema.
• Author a GraphQL RopeCheckpointReason enum with exactly Jim's supported values.
• Regenerate the request ABI without artifact edits.
• Keep one explicit, exhaustive conversion from the generated enum into Jim's native semantic enum.
• Add a bijection/exhaustiveness witness over every generated and native variant.
• Adding or removing a variant on either side fails generation, compilation, or the deterministic witness.
• Unknown wire values remain a typed, pre-admission failure.
• Document the later Edict replacement seam.

Related

• echo-wesley-gen emits uncompilable Rust for GraphQL enums echo#679 — enum-emitter correctness defect.
• Route checkpoint declarations through Echo #282 — checkpoint declaration slice that exposed this bridge.

[coderabbitai]

🔗 Related PRs

#23 - feat(echo): add Echo release gate witness [closed]
#26 - feat: report Echo witness evidence posture [closed]
#265 - CR-01: Separate checkpoints from Echo anchor authority [merged]
#280 - Add runtime-backed causal range evidence [merged]
#282 - Route checkpoint declarations through Echo [merged]

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