diff --git a/src/agents/subagent-orphan-recovery.test.ts b/src/agents/subagent-orphan-recovery.test.ts
index 5a112817177..5d71edb6ed6 100644
--- a/src/agents/subagent-orphan-recovery.test.ts
+++ b/src/agents/subagent-orphan-recovery.test.ts
@@ -3,7 +3,7 @@ import * as sessions from "../config/sessions.js";
 import * as gateway from "../gateway/call.js";
 import * as sessionUtils from "../gateway/session-utils.fs.js";
 import { recoverOrphanedSubagentSessions } from "./subagent-orphan-recovery.js";
-import * as subagentRegistry from "./subagent-registry.js";
+import * as subagentRegistryRuntime from "./subagent-registry-runtime.js";
 import type { SubagentRunRecord } from "./subagent-registry.types.js";
 
 // Mock dependencies before importing the module under test
@@ -28,7 +28,7 @@ vi.mock("../gateway/session-utils.fs.js", () => ({
   readSessionMessages: vi.fn(() => []),
 }));
 
-vi.mock("./subagent-registry.js", () => ({
+vi.mock("./subagent-registry-runtime.js", () => ({
   replaceSubagentRunAfterSteer: vi.fn(() => true),
 }));
 
@@ -103,7 +103,7 @@ describe("subagent-orphan-recovery", () => {
     expect(params.sessionKey).toBe("agent:main:subagent:test-session-1");
     expect(params.message).toContain("gateway reload");
     expect(params.message).toContain("Test task: implement feature X");
-    expect(subagentRegistry.replaceSubagentRunAfterSteer).toHaveBeenCalledWith(
+    expect(subagentRegistryRuntime.replaceSubagentRunAfterSteer).toHaveBeenCalledWith(
       expect.objectContaining({
         previousRunId: "run-1",
         nextRunId: "test-run-id",
@@ -379,7 +379,7 @@ describe("subagent-orphan-recovery", () => {
 
   it("does not retry a session after the gateway accepted resume but run remap failed", async () => {
     vi.mocked(gateway.callGateway).mockResolvedValue({ runId: "new-run" } as never);
-    vi.mocked(subagentRegistry.replaceSubagentRunAfterSteer).mockReturnValue(false);
+    vi.mocked(subagentRegistryRuntime.replaceSubagentRunAfterSteer).mockReturnValue(false);
 
     vi.mocked(sessions.loadSessionStore).mockReturnValue({
       "agent:main:subagent:test-session-1": {
diff --git a/src/agents/subagent-orphan-recovery.ts b/src/agents/subagent-orphan-recovery.ts
index 21025fd3bf3..50104d93915 100644
--- a/src/agents/subagent-orphan-recovery.ts
+++ b/src/agents/subagent-orphan-recovery.ts
@@ -21,7 +21,7 @@ import {
 import { callGateway } from "../gateway/call.js";
 import { readSessionMessages } from "../gateway/session-utils.fs.js";
 import { createSubsystemLogger } from "../logging/subsystem.js";
-import { replaceSubagentRunAfterSteer } from "./subagent-registry.js";
+import { replaceSubagentRunAfterSteer } from "./subagent-registry-runtime.js";
 import type { SubagentRunRecord } from "./subagent-registry.types.js";
 
 const log = createSubsystemLogger("subagent-orphan-recovery");
diff --git a/src/agents/subagent-registry-run-manager.ts b/src/agents/subagent-registry-run-manager.ts
index cc6c6c722fa..bd18b653c86 100644
--- a/src/agents/subagent-registry-run-manager.ts
+++ b/src/agents/subagent-registry-run-manager.ts
@@ -3,7 +3,7 @@ import { callGateway } from "../gateway/call.js";
 import { createSubsystemLogger } from "../logging/subsystem.js";
 import { createRunningTaskRun } from "../tasks/task-executor.js";
 import { type DeliveryContext, normalizeDeliveryContext } from "../utils/delivery-context.js";
-import { ensureRuntimePluginsLoaded } from "./runtime-plugins.js";
+import type { ensureRuntimePluginsLoaded as ensureRuntimePluginsLoadedFn } from "./runtime-plugins.js";
 import type { SubagentRunOutcome } from "./subagent-announce.js";
 import {
   SUBAGENT_ENDED_OUTCOME_KILLED,
@@ -35,7 +35,13 @@ export function createSubagentRunManager(params: {
   persist(): void;
   callGateway: typeof callGateway;
   loadConfig: typeof loadConfig;
-  ensureRuntimePluginsLoaded: typeof ensureRuntimePluginsLoaded;
+  ensureRuntimePluginsLoaded:
+    | typeof ensureRuntimePluginsLoadedFn
+    | ((args: {
+        config: ReturnType<typeof loadConfig>;
+        workspaceDir?: string;
+        allowGatewaySubagentBinding?: boolean;
+      }) => void | Promise<void>);
   ensureListener(): void;
   startSweeper(): void;
   stopSweeper(): void;
@@ -437,23 +443,28 @@ export function createSubagentRunManager(params: {
           completedAt: now,
         });
         const cfg = params.loadConfig();
-        params.ensureRuntimePluginsLoaded({
-          config: cfg,
-          workspaceDir: entry.workspaceDir,
-          allowGatewaySubagentBinding: true,
-        });
-        void emitSubagentEndedHookOnce({
-          entry,
-          reason: SUBAGENT_ENDED_REASON_KILLED,
-          sendFarewell: true,
-          accountId: entry.requesterOrigin?.accountId,
-          outcome: SUBAGENT_ENDED_OUTCOME_KILLED,
-          error: reason,
-          inFlightRunIds: params.endedHookInFlightRunIds,
-          persist: () => params.persist(),
-        }).catch(() => {
-          // Hook failures should not break termination flow.
-        });
+        void Promise.resolve(
+          params.ensureRuntimePluginsLoaded({
+            config: cfg,
+            workspaceDir: entry.workspaceDir,
+            allowGatewaySubagentBinding: true,
+          }),
+        )
+          .then(() =>
+            emitSubagentEndedHookOnce({
+              entry,
+              reason: SUBAGENT_ENDED_REASON_KILLED,
+              sendFarewell: true,
+              accountId: entry.requesterOrigin?.accountId,
+              outcome: SUBAGENT_ENDED_OUTCOME_KILLED,
+              error: reason,
+              inFlightRunIds: params.endedHookInFlightRunIds,
+              persist: () => params.persist(),
+            }),
+          )
+          .catch(() => {
+            // Hook failures should not break termination flow.
+          });
       }
     }
     return updated;
diff --git a/src/agents/subagent-registry.announce-loop-guard.test.ts b/src/agents/subagent-registry.announce-loop-guard.test.ts
index 90f30686f9d..51dbd032a9b 100644
--- a/src/agents/subagent-registry.announce-loop-guard.test.ts
+++ b/src/agents/subagent-registry.announce-loop-guard.test.ts
@@ -1,5 +1,4 @@
-import { afterEach, beforeEach, describe, expect, test, vi } from "vitest";
-import * as registry from "./subagent-registry.js";
+import { afterEach, beforeAll, beforeEach, describe, expect, test, vi } from "vitest";
 
 /**
  * Regression test for #18264: Gateway announcement delivery loop.
@@ -72,6 +71,13 @@ vi.mock("./timeout.js", () => ({
 }));
 
 describe("announce loop guard (#18264)", () => {
+  let registry: typeof import("./subagent-registry.js");
+
+  beforeAll(async () => {
+    vi.resetModules();
+    registry = await import("./subagent-registry.js");
+  });
+
   beforeEach(() => {
     vi.useFakeTimers();
     mocks.callGateway.mockClear();
diff --git a/src/agents/subagent-registry.runtime.ts b/src/agents/subagent-registry.runtime.ts
new file mode 100644
index 00000000000..8baf66a362d
--- /dev/null
+++ b/src/agents/subagent-registry.runtime.ts
@@ -0,0 +1,3 @@
+export { ensureContextEnginesInitialized } from "../context-engine/init.js";
+export { resolveContextEngine } from "../context-engine/registry.js";
+export { ensureRuntimePluginsLoaded } from "./runtime-plugins.js";
diff --git a/src/agents/subagent-registry.test.ts b/src/agents/subagent-registry.test.ts
index 435714345e3..3cb6ac856b9 100644
--- a/src/agents/subagent-registry.test.ts
+++ b/src/agents/subagent-registry.test.ts
@@ -277,7 +277,9 @@ describe("subagent registry seam flow", () => {
     await Promise.resolve();
 
     expect(mocks.runSubagentAnnounceFlow).not.toHaveBeenCalled();
-    expect(mocks.runSubagentEnded).toHaveBeenCalledTimes(1);
+    await vi.waitFor(() => {
+      expect(mocks.runSubagentEnded).toHaveBeenCalledTimes(1);
+    });
     await vi.waitFor(() => {
       expect(mocks.onSubagentEnded).toHaveBeenCalledWith({
         childSessionKey: "agent:main:subagent:child",
diff --git a/src/agents/subagent-registry.ts b/src/agents/subagent-registry.ts
index a570f526c9c..7cbcd35e62c 100644
--- a/src/agents/subagent-registry.ts
+++ b/src/agents/subagent-registry.ts
@@ -1,12 +1,12 @@
 import { loadConfig } from "../config/config.js";
-import { ensureContextEnginesInitialized } from "../context-engine/init.js";
-import { resolveContextEngine } from "../context-engine/registry.js";
+import type { ensureContextEnginesInitialized as ensureContextEnginesInitializedFn } from "../context-engine/init.js";
+import type { resolveContextEngine as resolveContextEngineFn } from "../context-engine/registry.js";
 import type { SubagentEndReason } from "../context-engine/types.js";
 import { callGateway } from "../gateway/call.js";
 import { onAgentEvent } from "../infra/agent-events.js";
 import { createSubsystemLogger } from "../logging/subsystem.js";
 import { type DeliveryContext, normalizeDeliveryContext } from "../utils/delivery-context.js";
-import { ensureRuntimePluginsLoaded } from "./runtime-plugins.js";
+import type { ensureRuntimePluginsLoaded as ensureRuntimePluginsLoadedFn } from "./runtime-plugins.js";
 import { resetAnnounceQueuesForTests } from "./subagent-announce-queue.js";
 import * as subagentAnnounceModule from "./subagent-announce.js";
 import type { SubagentRunOutcome } from "./subagent-announce.js";
@@ -64,35 +64,35 @@ const log = createSubsystemLogger("agents/subagent-registry");
 type SubagentRegistryDeps = {
   callGateway: typeof callGateway;
   captureSubagentCompletionReply: typeof subagentAnnounceModule.captureSubagentCompletionReply;
-  ensureContextEnginesInitialized: typeof ensureContextEnginesInitialized;
-  ensureRuntimePluginsLoaded: typeof ensureRuntimePluginsLoaded;
   getSubagentRunsSnapshotForRead: typeof getSubagentRunsSnapshotForRead;
   loadConfig: typeof loadConfig;
   onAgentEvent: typeof onAgentEvent;
   persistSubagentRunsToDisk: typeof persistSubagentRunsToDisk;
   resolveAgentTimeoutMs: typeof resolveAgentTimeoutMs;
-  resolveContextEngine: typeof resolveContextEngine;
   restoreSubagentRunsFromDisk: typeof restoreSubagentRunsFromDisk;
   runSubagentAnnounceFlow: typeof subagentAnnounceModule.runSubagentAnnounceFlow;
+  ensureContextEnginesInitialized?: typeof ensureContextEnginesInitializedFn;
+  ensureRuntimePluginsLoaded?: typeof ensureRuntimePluginsLoadedFn;
+  resolveContextEngine?: typeof resolveContextEngineFn;
 };
 
 const defaultSubagentRegistryDeps: SubagentRegistryDeps = {
   callGateway,
   captureSubagentCompletionReply: (sessionKey) =>
     subagentAnnounceModule.captureSubagentCompletionReply(sessionKey),
-  ensureContextEnginesInitialized,
-  ensureRuntimePluginsLoaded,
   getSubagentRunsSnapshotForRead,
   loadConfig,
   onAgentEvent,
   persistSubagentRunsToDisk,
   resolveAgentTimeoutMs,
-  resolveContextEngine,
   restoreSubagentRunsFromDisk,
   runSubagentAnnounceFlow: (params) => subagentAnnounceModule.runSubagentAnnounceFlow(params),
 };
 
 let subagentRegistryDeps: SubagentRegistryDeps = defaultSubagentRegistryDeps;
+let subagentRegistryRuntimePromise: Promise<
+  typeof import("./subagent-registry.runtime.js")
+> | null = null;
 
 let sweeper: NodeJS.Timeout | null = null;
 let listenerStarted = false;
@@ -107,6 +107,35 @@ const SUBAGENT_ANNOUNCE_TIMEOUT_MS = 120_000;
  */
 const LIFECYCLE_ERROR_RETRY_GRACE_MS = 15_000;
 
+function loadSubagentRegistryRuntime() {
+  subagentRegistryRuntimePromise ??= import("./subagent-registry.runtime.js");
+  return subagentRegistryRuntimePromise;
+}
+
+async function ensureSubagentRegistryPluginRuntimeLoaded(params: {
+  config: ReturnType<typeof loadConfig>;
+  workspaceDir?: string;
+  allowGatewaySubagentBinding?: boolean;
+}) {
+  const ensureRuntimePluginsLoaded = subagentRegistryDeps.ensureRuntimePluginsLoaded;
+  if (ensureRuntimePluginsLoaded) {
+    ensureRuntimePluginsLoaded(params);
+    return;
+  }
+  const runtime = await loadSubagentRegistryRuntime();
+  runtime.ensureRuntimePluginsLoaded(params);
+}
+
+async function resolveSubagentRegistryContextEngine(cfg: ReturnType<typeof loadConfig>) {
+  const runtime = await loadSubagentRegistryRuntime();
+  const ensureContextEnginesInitialized =
+    subagentRegistryDeps.ensureContextEnginesInitialized ?? runtime.ensureContextEnginesInitialized;
+  const resolveContextEngine =
+    subagentRegistryDeps.resolveContextEngine ?? runtime.resolveContextEngine;
+  ensureContextEnginesInitialized();
+  return await resolveContextEngine(cfg);
+}
+
 function persistSubagentRuns() {
   subagentRegistryDeps.persistSubagentRunsToDisk(subagentRuns);
 }
@@ -181,13 +210,12 @@ async function notifyContextEngineSubagentEnded(params: {
 }) {
   try {
     const cfg = subagentRegistryDeps.loadConfig();
-    subagentRegistryDeps.ensureRuntimePluginsLoaded({
+    await ensureSubagentRegistryPluginRuntimeLoaded({
       config: cfg,
       workspaceDir: params.workspaceDir,
       allowGatewaySubagentBinding: true,
     });
-    subagentRegistryDeps.ensureContextEnginesInitialized();
-    const engine = await subagentRegistryDeps.resolveContextEngine(cfg);
+    const engine = await resolveSubagentRegistryContextEngine(cfg);
     if (!engine.onSubagentEnded) {
       return;
     }
@@ -225,7 +253,7 @@ async function emitSubagentEndedHookForRun(params: {
   accountId?: string;
 }) {
   const cfg = subagentRegistryDeps.loadConfig();
-  subagentRegistryDeps.ensureRuntimePluginsLoaded({
+  await ensureSubagentRegistryPluginRuntimeLoaded({
     config: cfg,
     workspaceDir: params.entry.workspaceDir,
     allowGatewaySubagentBinding: true,
@@ -540,7 +568,11 @@ const subagentRunManager = createSubagentRunManager({
   persist: persistSubagentRuns,
   callGateway: (request) => subagentRegistryDeps.callGateway(request),
   loadConfig: () => subagentRegistryDeps.loadConfig(),
-  ensureRuntimePluginsLoaded,
+  ensureRuntimePluginsLoaded: (args: {
+    config: ReturnType<typeof loadConfig>;
+    workspaceDir?: string;
+    allowGatewaySubagentBinding?: boolean;
+  }) => ensureSubagentRegistryPluginRuntimeLoaded(args),
   ensureListener,
   startSweeper,
   stopSweeper,
@@ -597,6 +629,7 @@ export function resetSubagentRegistryForTests(opts?: { persist?: boolean }) {
   resumedRuns.clear();
   endedHookInFlightRunIds.clear();
   clearAllPendingLifecycleErrors();
+  subagentRegistryRuntimePromise = null;
   resetAnnounceQueuesForTests();
   stopSweeper();
   restoreAttempted = false;