feat(gts): enforce x-gts-closed-derivations in OP#12 chain validation

[AndrejK666]

Summary

Implements the x-gts-closed-derivations schema modifier proposed in GlobalTypeSystem/gts-spec# (0.14 draft, §9.11.4): a base type may require every derived schema to resolve to a closed content model at its own top level. Enforced in validate_schema_chain (OP#12) next to the existing x-gts-final guard.

Changes
gts/src/schema_modifiers.rs
new constant X_GTS_CLOSED_DERIVATIONS with doc comment;
validate_schema_modifiers: boolean-only value, top-level placement (same fail-fast rule as the other modifiers), and rejection of the meaningless x-gts-final + x-gts-closed-derivations combination.
gts/src/store.rs — in validate_schema_chain, for each (base, derived) pair: if the base declares the modifier, the derived schema's effective top-level additionalProperties (via the existing extract_effective_schema, which already folds allOf through the closedness-preserving lattice) must be false; otherwise StoreError::ValidationError naming the modifier, the base and the derived id.
gts/src/store_test.rs — five tests:
closed derived schema under a closed-derivations base → passes;
derived with additionalProperties: true → rejected (message names the modifier);
derived with additionalProperties omitted (default-open) → rejected;
closedness contributed by an allOf conjunct → passes;
final + closed-derivations on one schema → modifier validation error.
Why only direct derivations are checked

A closed derived level already prevents grandchildren from adding properties (§3.1), and a grandchild re-opening the level would accept instances its closed parent rejects — failing derivation compatibility (§4.1) through the existing checks. See spec §9.11.4 item 3.

Testing
bash
cargo test -p gts

All existing tests pass unchanged (the modifier is opt-in; schemas without it are unaffected).

Related
Spec: GlobalTypeSystem/gts-spec#
Motivating discussion: gears-rust tenant-metadata envelope (open abstract base + mandatory-closed derived metadata schemas); pairs with the planned open-content-model support in struct_to_gts_schema.

Summary by CodeRabbit

• New Features

  • Added support for marking schemas as requiring closed derived schemas.
  • Derived schemas must explicitly disallow additional properties when this setting is enabled.
  • Added validation for supported placement and boolean configuration.

• Bug Fixes

  • Prevented incompatible use of closed-derivation and final schema settings.
  • Improved validation errors for invalid or open derived schemas.

• Tests

  • Added coverage for valid closed schemas, composed schemas, and rejected configurations.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 532b4030-94b0-42d4-ae1d-1f497128c5f8

📥 Commits

Reviewing files that changed from the base of the PR and between c83b308 and 671bf54.

📒 Files selected for processing (3)

• gts/src/schema_modifiers.rs
• gts/src/store.rs
• gts/src/store_test.rs

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📝 Walkthrough

Walkthrough

The PR adds x-gts-closed-derivations, validates its schema placement and compatibility, enforces closed derived schemas during chain validation, and adds tests for accepted and rejected derivation patterns.

Changes

Closed derivation validation

Layer / File(s)	Summary
Modifier contract and placement validation gts/src/schema_modifiers.rs	Adds the public modifier constant. Validates boolean type, top-level placement, and incompatibility with x-gts-final.
Schema-chain closedness enforcement gts/src/store.rs	Rejects derived schemas whose effective top-level content model does not set additionalProperties to false.
Closed derivation test coverage gts/src/store_test.rs	Tests explicit closedness, explicit openness, omitted additionalProperties, allOf closedness, and conflicting modifiers.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant BaseSchema
  participant validate_schema_chain
  participant DerivedSchema
  BaseSchema->>validate_schema_chain: declare x-gts-closed-derivations
  validate_schema_chain->>DerivedSchema: resolve top-level content model
  DerivedSchema-->>validate_schema_chain: return additionalProperties setting
  validate_schema_chain-->>BaseSchema: accept or return ValidationError

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Possibly related PRs

• GlobalTypeSystem/gts-rust#80: Extends related schema modifier validation and derivation-chain logic.
• GlobalTypeSystem/gts-rust#90: Modifies schema closedness and additionalProperties handling.
• GlobalTypeSystem/gts-rust#92: Modifies GTS schema modifier handling and derivation-chain enforcement.

Suggested reviewers: aviator5, artifizer

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: enforcing x-gts-closed-derivations during OP#12 chain validation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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