feat(schemas): add SeamDefinition schema — typed seam registry object [T0-2]

[mdheller]

Implements T0-2. Adds schemas/SeamDefinition.json + 3 example seams (SEAM-002/008/013) + validator wired into make validate.

Verification

• python3 tools/validate_seam_definition_examples.py → OK: SeamDefinition schema valid; 3 seams validated (SEAM-002, SEAM-008, SEAM-013); 5 rejection invariants enforced (R1-R5)
• make validate-duplicate-schema-ids → OK: 324 unique schema $id values
• make validate → OK: validate

Acceptance criteria

• Schema validates against draft 2020-12
• implementation_status enum contains exactly four values (asserted by validator)
• Example covers ≥3 seams
• make validate passes

Rejection invariants: R1 bad status · R2 empty gate_requirements · R3 missing seam_id · R4 malformed seam_id · R5 bad priority.

Closes #229

[Copilot]

Pull request overview

This PR implements Issue #229 (T0-2) by introducing a new Draft 2020-12 JSON Schema (SeamDefinition) plus validated example fixtures, and wiring a dedicated validator into make validate so the spec stays fixture-backed and regression-checked.

Changes:

• Added schemas/SeamDefinition.json defining the canonical typed seam registry object (including required gate_requirements, implementation_status, and priority enums).
• Added three examples/seam-definition*.json fixtures (SEAM-002, SEAM-008, SEAM-013) and a validator (tools/validate_seam_definition_examples.py) that enforces both positive validation and rejection invariants (R1–R5).
• Integrated seam validation into the Makefile via validate-seam-definition-examples and included it in the validate meta-target.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tools/validate_seam_definition_examples.py	Adds schema+fixtures validator with enum assertion and negative controls (R1–R5).
schemas/SeamDefinition.json	Introduces the SeamDefinition Draft 2020-12 schema and required fields/enums.
Makefile	Wires the new seam-definition validator into make validate.
examples/seam-definition.json	Adds SEAM-002 example instance.
examples/seam-definition.seam-008.json	Adds SEAM-008 example instance.
examples/seam-definition.seam-013.json	Adds SEAM-013 example instance.

Suppressed comments (2)

schemas/SeamDefinition.json:40

• gate_requirements is required/non-empty via minItems: 1, but individual entries can still be empty strings. Enforcing minLength on each item better matches the intent (“no stated gate is not actionable”) and is consistent with other schemas’ string arrays.

      "items": { "type": "string" },

schemas/SeamDefinition.json:51

• linked_repos currently allows empty-string entries. Consider requiring non-empty strings for consistency with other string-array fields and to avoid placeholder/blank values silently validating.

      "items": { "type": "string" },