Add optional Agent Guild endpoint observation block

[AgentTanuki]

Adds an optional Agent Guild block for observing an explicitly supplied public HTTPS agent endpoint. It shares that URL with Guild and returns bounded check statuses, failed checks, unknowns and fixed limitations. It does not authorize delegation, invoke a target task, or turn observations into a safety guarantee.

The operation uses Sim’s native request path, redirects, socket timeout and parent cancellation. It performs no automatic retries, matches the returned target exactly, rejects incompatible responses, and applies a 64 KiB projection limit after the native transport cap. Includes registry entries, catalog templates and opt-in skill suggestions, generated metadata/docs, and the existing neutral search icon.

Validation includes the real Serializer → GenericBlockHandler → executeTool → pinned HTTP transport with only HTTP/DNS responses substituted, plus contribution contract tests, application type checking, generated metadata/docs/catalog checks and boundary audits. The graph baseline refresh records an intentional one-module block addition; exact staging comparison is 0/+1 modules across all 75 guarded entries, with no executable-registry reachability. The full generated refresh also incorporates drift already present at the pinned staging commit.

Validation results: 37/37 native execution cases (independently repeated), 21/21 contribution contract tests, full application type checking, and the required generation/boundary checks passed. Network responses were substituted; live provider availability and authorization involving persisted user/workspace state were not exercised. The native socket timeout is not a total deadline.

The generated documentation is preserved exactly as emitted by the existing generator. Its trailing whitespace produces two cosmetic diff-check findings; generated-doc freshness and original-source whitespace checks pass.

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