[davireis]

What I did

Restored the identical-resource fast path in importResource that #835 removed: when a resource re-imported through another include path is deeply equal to the already-imported definition, skip the merge. Genuinely different definitions keep the #835 override-merge behavior. Added a regression test with a diamond include fixture.

Why

Since #835, a file reached through multiple include: paths (a diamond) is re-merged once per path, and list-valued extension fields get their entries appended per re-merge — a service included through N paths ends with N copies of every x-* list entry:

# base.yaml
services:
  shared:
    image: busybox
    build:
      context: .
      x-bake:
        cache-from:
          - type=registry,ref=example/cache:a
# left.yaml / right.yaml:   include: [./base.yaml]
# compose.yaml:             include: [./left.yaml, ./right.yaml]

docker compose config | grep -c 'example/cache:a' → 1 on CLI v2.40.3 (compose-go v2.9.1), 2 on v5.0.0+/v2.10.0+; each additional include path adds another copy. Bisected to 3d3411d (#835). Spec-schema fields are unaffected (normalized downstream), which is why this went unnoticed.

Real-world impact: a monorepo integration-test tree with ~60 include paths to shared services saw its resolved config output grow from 2,043 to 127,725 cache entries (1.1 MB → 21 MB), and resolved output became dependent on which Docker Desktop version a developer runs.

Testing

• New TestLoadWithDiamondInclude fails on master (2 != 1) and passes with the fix.
• go test ./loader/ ./override/ pass.