Fixes #2524.

Problem

mergeOpenapiSchemas only errored on a type conflict when both members declared a type; otherwise it kept the first member's type, silently discarding the second's. Because allOf members merge pairwise in order, the generated Go shape depended on member ordering (see the issue for the repro — a struct in one order, any in the other).

Format had the mirror-image problem: any mismatch errored, including set-vs-unset, so the allOf decorator idiom over a $ref to a format-carrying scalar failed generation outright:

NullableUuid:
  allOf:
    - $ref: "#/components/schemas/Uuid"   # type: string, format: uuid
    - description: decorated              # no format -> "can not merge incompatible formats"

Fix

Both fields now follow the same one-sidedness rule: when exactly one member declares a type/format, it propagates to the merged schema; when both declare and they differ, the existing errors remain.

Compatibility notes

• Repo-wide make generate changes no existing committed .gen.go — the entire test corpus is unaffected.
• The format half is purely additive: specs that previously failed generation now work.
• The type half changes output only for specs whose allOf mixes a typeless member with a non-object-typed member — output there was order-dependent (and per JSON Schema semantics, wrong: properties doesn't constrain non-object instances, so allOf: [{properties…}, {type: string}] only ever validates strings). Specs hiding two conflicting types behind a typeless member (e.g. [{properties…}, {type: string}, {type: number}]) now hit the existing incompatible-types error instead of silently generating a struct; such specs are unsatisfiable. compatibility.old-merge-schemas routes to the untouched legacy codepath and remains the escape hatch.

Tests

• Unit tests in merge_schemas_test.go for both propagation rules, order symmetry, and the preserved error cases.
• Conformance fixtures in internal/test/aggregates/allof/: the issue's repro in both member orders (both lower to any), single-type in both orders (both lower to string), and the format-decorator idiom in both orders (both lower to openapi_types.UUID), pinned by TestIssue2524.

make tidy && make test && make generate && make lint all pass.

🤖 Generated with Claude Code