openapi: two schema composition tests assert less than their names claim #742

Problem

Two tests in compilers/openapi/internal/schema/compose_test.go cannot fail for the reason they were written.

• TestUnionCombinators_CoDeclaredKeepsTheBoundsWrittenBesideIt declares a wantDiag column and, after its other assertions, checks that the openapi/degraded-construct diagnostic at /components/schemas/A contains it. No case sets wantDiag, so every case returns before that check. The last case that set it ("kept minimum as the tighter of the two", added in fix(compilers/openapi): keep bounds beside a preserved union #363) was removed in feat(ir)!: land the IR 0.4.0 stack #464, which left the column and the branch in place.
• TestAllOf_BoolBranchSkippedInCompositionRequired exercises the bs == nil guard in compositionRequired (compose.go), which skips an allOf branch that is a bare boolean schema. The guard has no observable effect: GetRequired is nil-safe, so without it the loop appends nothing for that branch either. Deleting the guard leaves the package green.

Reproduction

$ git grep -n 'wantDiag' -- compilers/openapi/internal/schema/compose_test.go

prints the field, the if tc.wantDiag == "" early return and the assert.Contains, and no case literal.

For the guard, delete the three lines of if bs == nil { continue } in compositionRequired and run:

$ go test ./compilers/openapi/internal/schema/ -count=1
ok  	github.com/dexpace/morphic/compilers/openapi/internal/schema

Why it matters

The wantDiag column reads as coverage of what reading the co-declared bounds reports, and nothing checks it. A change that stops reporting, or reports the wrong thing, passes.

The guard is harmless, but it is the only reason the bool-branch test's name points at compositionRequired: the test pins the lowered result, which holds with or without it.

Options

• Give the union-combinators table a case that sets wantDiag to what the bounds reading reports today, or drop the column and the branch if it reports nothing worth pinning.
• Delete the guard, since the code reads the same without it, or keep it and name the test for the behaviour it pins.