Expose frozen Session configuration and adapter capabilities

[SaladDay]

Clients can now inspect the model, harness and safe provider configuration frozen for a Session, including each selection's recorded source. The new read-only endpoint uses a safe projection saved atomically at creation, without decrypting secrets or rereading current Agent/deployment defaults. Deployment provider details are redacted, historical provenance stays unknown, and tenant isolation and retry/lifecycle immutability are preserved.

Provider configuration discovery is available through GET /v1/agents/core/startup-configuration?include=configuration_capabilities. The default startup response remains unchanged for installed strict clients. One immutable adapter declaration registry supplies validation, discovery and optional safe native adapter descriptors; Core adds deployment selections and admission restrictions. Support and enablement remain separate from live readiness.

Includes migration 000060, generated SQL/OpenAPI, client methods and defensive response projections, examples and architecture documentation. No configuration mutation, Provider/model catalog, live probe, Session migration or Web redesign.

Validation:

• Required make check ran: backend/PostgreSQL/generated/build/client/Web-unit stages passed; 123 browser cases passed and four Dashboard cases failed. All four failures also reproduce on pristine c5cb6b5, so the full gate is not green.
• After registry consolidation, daemon/shared Go checks passed except an old CLI descriptor assertion; that assertion was updated for the new optional metadata and the affected package passed. API/server/registry checks, focused PostgreSQL regressions, TypeScript checks and all 400 client tests passed. Standalone builds and remaining MiniMax/executor checks passed.
• Isolated real-model tests passed for Codex, Claude SDK and MiniMax Code: six native Turns including Core restart and microsandbox resume, immutable projections after Agent edit/delete and deployment changes, idempotent retry, all inheritance sources, historical unknown, exact foreign/missing/malformed404 parity, deployment redaction and reads independent of credential decryption. Reads did not add execution records.
• The final rebuilt candidate passed isolated startup/read verification against all retained Sessions with identical projections and Turn IDs. A fresh independent blind review of all 47 changed files found no actionable issues. Production services were not changed.

Tasks: SESSION-EXEC-CONFIG-001 and HARNESS-CONFIG-CAPABILITIES-001.
Details: https://vrfi1sk8a0.feishu.cn/wiki/EA3CwVSRviqe1XkZ0tAcq7FqnFc