[xiaoqi-7]

Reason for Change:

Implement phase 2.1: validate gateway policy configuration and map scanner settings to shared core configuration/build APIs. The 77-line policy adapter delegates to core; it does not define a scanner registry, scanner implementations, or a guardrail engine.

Requirements

• added unit tests and e2e tests (if applicable).

Issue Fixed:

Related to #226.

Notes for Reviewers:

• Based on upstream main 2ea0177, including refactor: adopt shared core streaming and holdback APIs in ext_proc #257.
• Pins the published PyPI dependency kaito-guardrail-core==0.2.0, replacing the temporary prerequisite source archive. The 0.2.0 release provides the shared streaming and configuration/build APIs.
• Accept action, blockMessage, and a non-empty ordered scanners list. Default to block; allow per-scanner action overrides. Reject malformed policy/scanner entries rather than silently skipping protection.
• Core owns scanner names, normalization, validation, and construction. Tests exercise all eight real shared scanners in block/redact modes and verify validation errors and construction failures.
• Envoy Process remains UNIMPLEMENTED. Policy file loading, execution, streaming scanner adaptation, deployment, and real Envoy E2E remain out of scope.
• Validation at 6716ffa: a fresh Python 3.12 environment installed the published core 0.2.0 package; all 82 ext_proc tests, pip check, and git diff --check passed. The dependency contract test now requires the exact published version pin.
• Local image build encountered an external PyPI TLS handshake failure in the unchanged pip bootstrap step. The updated CI run passed, including published core installation, all ext_proc tests, the ext_proc image build, lint, and amd64/arm64 test and image-build jobs. All PR checks are green.