From 375c104b325a64b76f0ba7650c65a429cad47496 Mon Sep 17 00:00:00 2001
From: Jerop Kipruto <jerop@google.com>
Date: Sun, 8 Feb 2026 20:57:01 -0500
Subject: [PATCH] fix(core): ensure `enter_plan_mode` tool registration
 respects `experimental.plan` (#18587)

---
 packages/core/src/config/config.test.ts | 24 +++++++++++++++++++++++-
 packages/core/src/config/config.ts      | 10 ++++++++--
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/packages/core/src/config/config.test.ts b/packages/core/src/config/config.test.ts
index 312c1b5b0a..d2c460d240 100644
--- a/packages/core/src/config/config.test.ts
+++ b/packages/core/src/config/config.test.ts
@@ -2333,10 +2333,11 @@ describe('syncPlanModeTools', () => {
     expect(registeredTool).toBeInstanceOf(ExitPlanModeTool);
   });
 
-  it('should register EnterPlanModeTool and unregister ExitPlanModeTool when NOT in PLAN mode', async () => {
+  it('should register EnterPlanModeTool and unregister ExitPlanModeTool when NOT in PLAN mode and experimental.plan is enabled', async () => {
     const config = new Config({
       ...baseParams,
       approvalMode: ApprovalMode.DEFAULT,
+      plan: true,
     });
     const registry = new ToolRegistry(config, config.getMessageBus());
     vi.spyOn(config, 'getToolRegistry').mockReturnValue(registry);
@@ -2360,6 +2361,27 @@ describe('syncPlanModeTools', () => {
     expect(registeredTool).toBeInstanceOf(EnterPlanModeTool);
   });
 
+  it('should NOT register EnterPlanModeTool when experimental.plan is disabled', async () => {
+    const config = new Config({
+      ...baseParams,
+      approvalMode: ApprovalMode.DEFAULT,
+      plan: false,
+    });
+    const registry = new ToolRegistry(config, config.getMessageBus());
+    vi.spyOn(config, 'getToolRegistry').mockReturnValue(registry);
+
+    const registerSpy = vi.spyOn(registry, 'registerTool');
+    vi.spyOn(registry, 'getTool').mockReturnValue(undefined);
+
+    config.syncPlanModeTools();
+
+    const { EnterPlanModeTool } = await import('../tools/enter-plan-mode.js');
+    const registeredTool = registerSpy.mock.calls.find(
+      (call) => call[0] instanceof EnterPlanModeTool,
+    );
+    expect(registeredTool).toBeUndefined();
+  });
+
   it('should call geminiClient.setTools if initialized', async () => {
     const config = new Config(baseParams);
     const registry = new ToolRegistry(config, config.getMessageBus());
diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index 4df65f51a2..92e20f9163 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -1540,8 +1540,14 @@ export class Config {
       if (registry.getTool(EXIT_PLAN_MODE_TOOL_NAME)) {
         registry.unregisterTool(EXIT_PLAN_MODE_TOOL_NAME);
       }
-      if (!registry.getTool(ENTER_PLAN_MODE_TOOL_NAME)) {
-        registry.registerTool(new EnterPlanModeTool(this, this.messageBus));
+      if (this.planEnabled) {
+        if (!registry.getTool(ENTER_PLAN_MODE_TOOL_NAME)) {
+          registry.registerTool(new EnterPlanModeTool(this, this.messageBus));
+        }
+      } else {
+        if (registry.getTool(ENTER_PLAN_MODE_TOOL_NAME)) {
+          registry.unregisterTool(ENTER_PLAN_MODE_TOOL_NAME);
+        }
       }
     }