Add a middleware system that wraps around build pipeline phases with
before/after semantics, built on the existing command hook and container
hook fundamentals. Middleware supports rich trigger conditions (phase,
provider, platform, environment expressions), priority-based ordering
with wrapping semantics, and both inline YAML and file-based definitions
from game-ci/middleware/.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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