test: cover agentId threading on plugin lease RPCs and call sites

Adds focused tests for every code path the agentId addition touches:

- environment-runtime.test.ts (4 new tests):
  - plugin-driver acquireLease forwards agentId in RPC payload when present
  - plugin-driver acquireLease omits agentId from RPC payload when null
  - sandbox-provider acquireLease forwards agentId when present
  - sandbox-provider resumeLease forwards agentId when reuseLease=true matches
  - seedEnvironment helper now exposes the seeded agentId

- environment-run-orchestrator.test.ts (2 new tests):
  - acquireForRun threads agentId through to runtime.acquireRunLease
  - logActivity records the same agentId on environment.lease_acquired
  - new vi.hoisted mocks for environmentService.getById + ensureLocalEnvironment

- agent-test-environment-routes.test.ts (1 new assertion):
  - ad-hoc operator test-environment probe calls acquireRunLease with
    agentId: null and heartbeatRunId: null (no agent context)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/src/__tests__/agent-test-environment-routes.test.ts

@@ -196,6 +196,15 @@ describe("agent test-environment route", () => {
       }),
       status: "failed",
     });
+    // Ad-hoc operator probes have no agent context — the route must pass
+    // agentId: null so plugin-backed providers don't accidentally scope the
+    // probe lease against some leftover agentId from the heartbeat path.
+    expect(mockEnvironmentRuntime.acquireRunLease).toHaveBeenCalledWith(
+      expect.objectContaining({
+        agentId: null,
+        heartbeatRunId: null,
+      }),
+    );
   });
 
   it("returns a diagnostic result instead of probing the host when the requested environment is missing", async () => {