Fail merged apps with conflicting schema names

[owjs3901]

Summary

• reject differently-shaped component schemas that share a name while exported apps are merged
• reuse CollectedMetadata::check_duplicate_schema_names() so identical definitions retain the existing silent deduplication behavior
• identify the parent/merged app origins in the diagnostic and span the error to the incoming app path in merge = [...]

Verified pre-change behavior

The pre-change behavior was silent first-wins, not last-wins. OpenApi::merge preserves the schema already present in self; compile-time app assembly starts with the parent spec and folds merged apps in declaration order. Therefore the parent wins over children, and among children the earlier entry wins over a later collision.

I verified this against the existing vespera_core merge contract before changing the macro. In the reported reproduction, Plugin A was merged before Plugin B, so both /api/example/items/ and /memo/collision-probe remained in paths, but components.schemas.ExampleItem retained only Plugin A's { id, name, description, createdAt } shape. Plugin B's runtime response { collisionMarker, count } was silently documented with Plugin A's incompatible schema.

The merge boundary only has each exported app's OpenAPI sidecar and the syn::Path entries supplied to vespera!(merge = [...]); original struct spans from child crates are no longer available. The diagnostic therefore points at the conflicting incoming app path and names both best-available origins (for example, plugin_a::PluginA and plugin_b::PluginB).

Tests

• cargo test --workspace
• bun run lint
• regression coverage for conflicting child schemas, identical shared schemas, and a schema defined once

The changepack records this as a minor vespera_macro change because previously silent collisions can now fail existing builds.

[github-actions]

Changepacks

vespera@0.3.1 - Cargo.toml

Maybe you forgot to write the following files to the latest version

vespera@0.3.1 → 0.3.2 - crates/vespera/Cargo.toml

Patch

• Auto-update: depends on 'vespera_macro' via a local workspace dependency

vespera_macro@0.3.1 → 0.4.0 - crates/vespera_macro/Cargo.toml

Minor

• Fail the build when merged apps define conflicting same-named OpenAPI schemas, turning a previously silent first-wins condition into an actionable compile error while preserving identical-schema deduplication.