refactor(session)!: remove public suspend and resume controls - #3409

Agent runtime lifecycle is already platform-managed. This removes the public Session suspend/resume RPCs, UI controls, and chat resume plumbing. Automatic quiescence keeps the Session READY, and the next interaction wakes the Actor through Substrate ingress.

Sandboxes retain explicit suspend/resume. Internal Session suspension remains for scheduled-run deadline cleanup when no scheduled task can be identified.

This intentionally breaks the Session API by removing SuspendSession, ResumeSession, and their four request/response messages. Generated bindings, callers, tests, and lifecycle docs are updated together.

flowchart LR
    client["Client"] -->|agent interaction| ingress["Substrate ingress"]
    ingress -->|wake| agent["Agent Actor"]
    quiescence["Session quiescence worker"] -->|suspend after settlement| agent
    client -->|explicit suspend/resume| service["SandboxService"]
    service -->|runtime lifecycle| sandbox["Sandbox Actor"]

Validation:

• Focused Go race suites passed for Session, Sandbox, Substrate, gRPC, MCP, A2A gateway, scheduled-run controller, and app wiring. Go lint and E2E compilation passed.
• UI typecheck and lint passed, along with 682 unit tests and 60 browser tests.
• Protobuf lint and full generation passed. A later repeat hit the Buf Python-plugin rate limit. Buf breaking reports only the intentional RPC/message removals.
• Live Kubernetes/Substrate E2Es and the full repository Go suite were not run.