[shivros]

Summary

Closes COD-508 by making typed HTTP-error const declarations strict at the real YAML loader boundary:

• preserves an omitted const as dynamic None;
• rejects explicit null, ~, empty YAML values, booleans, numbers, sequences, and mappings before generation;
• retains valid required string constants and the existing public Option<String> model;
• adds named source diagnostics for malformed declarations and source-qualified validation errors for optional string constants.

No generated fixture or public surface changed for valid definitions.

Evidence

Baseline before the fix, through hydra_core::load_api_definition, incorrectly accepted const: null as constant=None.

The new table-driven loader test derives temporary definitions from the committed HTTP-error fixture. It covers required and optional fields, omitted/dynamic behavior, escaped/empty/quoted scalar strings, all malformed YAML scalar/collection forms, named source diagnostics, and the existing required-only constant rule.

A real CLI boundary check now rejects an optional string constant before write with:

Error: validate API definition from api/operations.yaml
Caused by:
    operation status HTTP error response unavailable field error declares const but is optional; constants require required: true

Verification

cargo build --all-targets
cargo test --all-targets                 # 51 codegen + 14 Notes-surface + 6 security-scan tests
cargo test -p hydra-codegen --test codegen
cargo clippy --all-targets -- -D warnings
cargo fmt --all -- --check
(cd examples/notes && cargo run -p hydra-codegen --bin hydra-codegen -- check)
(cd examples/security-scan && cargo run -p hydra-codegen --bin hydra-codegen -- check)
git diff --check

All commands passed. The existing HTTP-error fixture's two temporary generated writes remained byte-identical, and both committed example artifact checks reported current output.

Scope

This is a bounded loader-validation correction only: no release, tag, dependency, consumer adoption, configuration, generated artifact, CLI/MCP behavior, SSE behavior, or runtime dispatch change.

[shivros]

🤖 Automated Review Panel

Reviewer A — GPT-5.6 Terra

APPROVE — no correctness blockers remain.

• Confirmed the raw-YAML pass rejects every supplied non-string const before typed generation, while omission still yields dynamic None.
• Confirmed valid escaped, empty, quoted numeric, and quoted boolean strings remain fixed required constants rather than constructor inputs.
• Confirmed the prior review finding is resolved: optional string constants now fail through the existing required-only rule with the API-definition source path. The regression asserts source, operation, response, and field diagnostics.
• Confirmed full local gates, deterministic fixture coverage, and both example checks are green.

Reviewer B — Gemini 3 Flash (OpenRouter)

APPROVE (minor non-blocking notes only).

• Confirmed strict null/tilde/boolean/numeric/collection rejection, named diagnostics, and unchanged valid-constant behavior.
• Noted the intentional two-pass loader parse used to retain raw-YAML diagnostic context while keeping direct HttpErrorField deserialization strict. This is bounded definition-load work, not a runtime-path regression.
• Noted only optional consistency/performance refinements; no correctness, goal-alignment, or convention violation was found.

Resolution and evidence

The first Reviewer A pass identified one real issue: optional string constants lacked source-path context. It was fixed before this final dual-model confirmation by wrapping semantic definition validation in the loader's source context and adding a regression assertion. The real hydra-codegen write boundary now emits:

Error: validate API definition from api/operations.yaml
Caused by:
    operation status HTTP error response unavailable field error declares const but is optional; constants require required: true

Final verified gates:

cargo build --all-targets
cargo test --all-targets
cargo test -p hydra-codegen --test codegen
cargo clippy --all-targets -- -D warnings
cargo fmt --all -- --check
(cd examples/notes && cargo run -p hydra-codegen --bin hydra-codegen -- check)
(cd examples/security-scan && cargo run -p hydra-codegen --bin hydra-codegen -- check)
git diff --check

All passed; the full suite contains 51 codegen tests, 14 Notes-surface tests, and 6 security-scan tests. The committed HTTP-error fixture's existing two-write byte-determinism test also remained green.

[shivros]

Auto-Merge Gate

Confidence: 0.93

The implementation directly satisfies COD-508: omitted const remains dynamic; every explicitly supplied non-string YAML value is rejected at load_api_definition; valid required string constants retain their existing public Option<String> semantics. The regression matrix exercises the real loader for required and optional fields and asserts named, source-qualified diagnostics.

Independent checks observed: CI Test and Creed context drift both succeeded. The PR review panel’s final disposition found no correctness blocker, and the linked Linear issue has no manual-review or do-not-auto-merge marker.

Scope limits reviewed: two files only; no release, deployment, credential, consumer, generated-artifact, or runtime dispatch change.