Collection requirements.txt ships a pip option line ('-c constraints.txt') that breaks ansible-builder EE builds #708

Summary

The collection's requirements.txt ships a pip option line alongside the PEP 508 requirements:

ansible
pydantic
requests
-c constraints.txt

ansible-builder's introspection passes each line of a collection's requirements.txt through as a requirement entry into the combined build-context requirements file. The -c constraints.txt line survives introspection verbatim:

$ ansible-builder introspect <collections_path>
python:
- 'pydantic  # from collection cisco.dcnm'
- 'requests  # from collection cisco.dcnm'
- -c constraints.txt

In the EE build context the relative path constraints.txt does not exist (pip resolves -c relative to the combined requirements file's directory, not the collection's), so the build fails:

ERROR: Could not open requirements file: [Errno 2] No such file or directory: '.../constraints.txt'

Any execution environment that includes cisco.dcnm therefore fails to build unless the collection's entire python-requirements passthrough is excluded.

Environment

• cisco.dcnm: 3.12.0 and 3.12.1 (both ship the line; constraints.txt in the collection contains ansible<12)
• ansible-builder: 3.1.1 (definition schema v3)
• Base image: registry.redhat.io/ansible-automation-platform-25/ee-supported-rhel8:latest

Expected behavior

requirements.txt contains only PEP 508 requirement lines so EE builds that include the collection succeed. If the ansible<12 constraint matters for the collection, it could be expressed as a direct requirement bound (or documented), rather than a -c option line that only resolves in the collection's own directory.

Workaround we run today

In the EE definition (schema v3), exclude the collection's python passthrough entirely and re-declare its real dependencies once at the EE level:

dependencies:
  exclude:
    python:
      all_from_collections:
        - cisco.dcnm
  python: requirements.txt   # re-declares pydantic + requests>=2.28 once

Happy to provide anything else that helps reproduce.