fix(agent): verify remote DWN responses

[LiranCohen]

Summary

• authenticate remote protocol configurations before they can drive encryption policy
• authenticate returned RecordsWrite/RecordsDelete artifacts, bind them to the original query/read filter, and verify inline or streamed bytes against the signed CID and size
• authenticate initial RecordsSubscribe snapshots with the same rules as RecordsQuery and close rejected subscriptions before endpoint fallback
• verify app-facing signed and anonymous remote paths at each endpoint, pin lazy record reads to their original data version, and correct the anonymous subscription transport shape
• disclose the security rationale and migration guidance for the removed social protocol catalog

Security boundary

• protocol definitions used for encryption policy must be signed directly by the target DID
• these checks prove artifact authorship and integrity, not response completeness, freshness, or target-tenant admission; those require a tenant-authenticated state commitment
• RecordsCount values carry no signed artifact and remain assertions by the remote DWN
• streamed bytes are authenticated at successful EOF; consumers that cannot tolerate an unauthenticated prefix must buffer through successful completion before using the bytes
• initial subscription snapshots are verified, while subsequent live subscription events remain outside this response-verification boundary

Follow-ups

• fix(dwn): prevent self-issued protocol roles from granting authority #1477 tracks the engine-level role self-mint authorization defect
• perf(dwn): amortize subscription delivery authority checks safely #1478 tracks safe amortization of per-event subscription authority checks

Test plan

• bun run lint
• bun run --filter @enbox/dwn-sdk-js build
• bun run --filter @enbox/agent build
• bun run --filter @enbox/api build
• focused agent verifier, endpoint fallback, protocol-cache, and anonymous API tests
• focused API lazy-record tests
• full CI matrix and SonarCloud on the prior head; rerunning for the snapshot follow-up

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
96.5% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud