feat(engine): materialize composed Diagram ViewData

[Dencyuman]

Summary

• materialize composed Diagram ViewData for edge, nest, overlay, badge, and hide projection modes
• apply deterministic projection override, nesting conflict, placement, and support-item rules
• preserve complete Entity, Relation, row, cell, and state source references with stable occurrence-local keys
• reject cycles, malformed endpoint closure, duplicate inputs, and unsupported projection combinations without partial publication

Linked Issues

• Closes [Feature]: Materialize composed Diagram ViewData #67

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Scope

• Documentation only
• LDL / schema / protocol
• Engine / Runtime / Query / View
• SDK / MCP / client integration
• Server / storage / realtime / access
• Registry / packs / templates
• Release / governance / legal

Checks

• I did not add secrets, customer data, private deployment config, or local agent config.
• I checked the package boundary and licensing docs for affected paths.
• I updated generated artifacts or fixtures if a schema changed.
• I documented any public API, protocol, license, or release impact.
• I identified compatibility or migration impact, or confirmed there is none.
• I identified whether a release note is required.

Contract Impact

• Affected components and delivery bundles: Go Engine in-process Diagram ViewData materialization only.
• LDL / schema / protocol / container impact: No language, schema, protocol, or container change. Protocol generation remains deferred to [Feature]: Expose complete ViewData through Engine Protocol #71.
• State or data migration impact: None.
• License or dependency impact: None.
• Release note: Not required before the complete ViewData milestone is released.

Validation

• make ci
• Engine package coverage: 88.1% (required 88.0%)
• Patch coverage: 84.0% (required 80.0%)
• deterministic native/WASM/release-set build and packaged tests