refactor(supervisor): remove legacy supervisor control RPCs after session migration

[pimlock]

Problem Statement

#1731 should keep the existing supervisor control RPCs during the session-control migration so rollout is reversible and mixed-version gateways/supervisors remain safe. Once the session path is implemented, feature-flagged, and exercised, the redundant legacy RPCs should be deprecated or removed in a separate cleanup.

Proposed Design

After the session-control path is stable:

• Migrate supervisor call sites away from legacy polling/report RPCs.
• Remove or deprecate redundant RPCs where the session-control equivalent is adopted:
  • GetSandboxConfig
  • GetSandboxProviderEnvironment
  • PushSandboxLogs
  • ReportPolicyStatus
  • SubmitPolicyAnalysis
  • Inference.GetInferenceBundle
• Remove compatibility fallback code only after the supported rollout window is clear.
• Update generated clients, server handlers, tests, and docs together.
• Keep user-facing read APIs, such as log retrieval or policy status reads, if they are still independently useful.

Alternatives Considered

• Remove legacy RPCs inside Push gateway-owned desired state to supervisors #1731: rejected because it makes the first migration harder to review, harder to roll back, and riskier for mixed-version deployments.
• Keep legacy RPCs indefinitely: acceptable during rollout, but it leaves duplicate control paths and makes future behavior harder to reason about.

Agent Investigation

Current code still uses separate RPCs for the control/reporting paths while ConnectSupervisor only carries session lifecycle, heartbeat, and relay lifecycle messages. The initial #1731 implementation should make legacy RPC handlers thin wrappers around shared helpers, then route session messages through the same helpers. This follow-up removes the wrappers and fallback paths after the new path is proven.

Definition of Done

• Confirm the session-control path is enabled and covered by tests/e2e for supported deployments.
• Remove or deprecate redundant proto RPCs and regenerate bindings.
• Remove server handlers that no longer have supported callers.
• Remove supervisor polling/reporting call sites that no longer need fallback.
• Update docs that mention legacy polling/reporting behavior.
• Add release/compatibility notes if this is a breaking protocol cleanup.

Related

• Follow-up to Push gateway-owned desired state to supervisors #1731

[github-actions]

This issue has had no activity for 14 days and is now marked stale. It may be closed in 7 days if there is no further activity. Comment or remove the state:stale label to keep it open.

[jolong-debug]

@pimlock This issue has had no activity since July 8. With 0.1.0 quickly approaching, please let me know if this is still planned for 0.1.0. If so, is the work blocked, or is this no longer needed?