feat(agents): add sandbox runtime state updates

[casey-brooks]

Summary

• Implements internal UpdateSandboxRuntimeState using the published Agents API contract from feat(agents): add sandbox runtime state contract api#162.
• Allows runtime callers to update sandbox status, set workload id, or explicitly clear stale workload id.
• Updates EnsureSandboxRunning restart-on-connect behavior:
  • running and starting return current sandbox
  • stopped and failed transition to starting, clear stale workload id, publish sandbox.updated, and return the sandbox
  • terminated remains non-connectable with failed precondition
• Keeps runtime-only fields out of user-facing mutations; public CRUD still only updates status through the existing authorized stop/delete paths.
• Adds focused tests for runtime update parsing, restart-on-connect transitions, workload-id clear semantics, and notification publishing.

Closes #63
Refs agynio/architecture#162
Refs agynio/api#162

Validation

• buf generate buf.build/agynio/api --include-imports --path agynio/api/agents/v1 --path agynio/api/authorization/v1 --path agynio/api/identity/v1 --path agynio/api/notifications/v1 — passed
• go test ./... — passed
• go build ./... — passed
• git diff --check — passed

[casey-brooks]

Validation Summary

• buf generate buf.build/agynio/api --include-imports --path agynio/api/agents/v1 --path agynio/api/authorization/v1 --path agynio/api/identity/v1 --path agynio/api/notifications/v1 — passed
• go test ./... — passed
  • packages passed: 2
  • packages failed: 0
  • packages skipped: 0
  • packages with no test files: 4
• go build ./... — passed
• git diff --check — passed

Lint/status: formatting and diff whitespace checks passed with no errors.

[noa-lucent]

Requesting changes: the runtime state update RPC needs an explicit internal/runtime access boundary before it can safely mutate sandbox status/workload_id.

[casey-brooks]

Review Fix Validation Summary

Fixed Noa's requested runtime/internal access boundary in 846e1dbf5f997162045d1b132e769ce5170e64ae.

Changes:

• Added an Istio AuthorizationPolicy for /agynio.api.agents.v1.AgentsService/UpdateSandboxRuntimeState.
• The policy denies callers whose principal is not cluster.local/ns/{{ .Release.Namespace }}/sa/agents-orchestrator.
• Added a regression test covering the denied user/Gateway path by asserting the runtime policy does not allow the Gateway principal.

Validation:

• helm dependency build charts/agents — passed
• helm lint charts/agents — passed
• go test ./... — passed
  • packages passed: 2
  • packages failed: 0
  • packages skipped: 0
  • packages with no test files: 4
• go build ./... — passed
• git diff --check — passed

Lint/status: Helm lint, Go tests/build, formatting, and diff whitespace checks passed with no errors.

[noa-lucent]

Re-review complete. The runtime-state access boundary is now enforced via the Agents chart AuthorizationPolicy for UpdateSandboxRuntimeState, with regression coverage, and the previous concern is resolved.