diff --git a/extensions/vscode/src/activation/InlineTipManager.ts b/extensions/vscode/src/activation/InlineTipManager.ts
index 4a544147cc3..0921732c99b 100644
--- a/extensions/vscode/src/activation/InlineTipManager.ts
+++ b/extensions/vscode/src/activation/InlineTipManager.ts
@@ -236,7 +236,7 @@ export class InlineTipManager {
 
   private createSvgTooltipDecoration() {
     var backgroundColour = "#333333";
-    if (this.theme) {
+    if (this.theme?.colors?.["editor.background"]) {
       backgroundColour = this.theme.colors["editor.background"];
     }
     return vscode.window.createTextEditorDecorationType({
@@ -274,7 +274,8 @@ export class InlineTipManager {
           {
             ...baseTextConfig,
             x: SVG_CONFIG.chatLabelX,
-            fill: this.theme?.colors["editor.foreground"] ?? SVG_CONFIG.stroke,
+            fill:
+              this.theme?.colors?.["editor.foreground"] ?? SVG_CONFIG.stroke,
           },
           SVG_CONFIG.chatLabel,
         )
@@ -291,7 +292,8 @@ export class InlineTipManager {
           {
             ...baseTextConfig,
             x: SVG_CONFIG.editLabelX,
-            fill: this.theme?.colors["editor.foreground"] ?? SVG_CONFIG.stroke,
+            fill:
+              this.theme?.colors?.["editor.foreground"] ?? SVG_CONFIG.stroke,
           },
           SVG_CONFIG.editLabel,
         )
diff --git a/extensions/vscode/src/activation/InlineTipManager.vitest.ts b/extensions/vscode/src/activation/InlineTipManager.vitest.ts
new file mode 100644
index 00000000000..65ee72ba204
--- /dev/null
+++ b/extensions/vscode/src/activation/InlineTipManager.vitest.ts
@@ -0,0 +1,59 @@
+import { describe, expect, it, vi } from "vitest";
+
+// createSvgTooltipDecoration only calls window.createTextEditorDecorationType,
+// but importing the module pulls in helpers that read the workspace config, so
+// the mock covers that surface too.
+vi.mock("vscode", () => ({
+  window: {
+    createTextEditorDecorationType: vi
+      .fn()
+      .mockReturnValue({ dispose: vi.fn() }),
+  },
+  workspace: {
+    getConfiguration: vi.fn().mockReturnValue({ get: vi.fn() }),
+    onDidChangeConfiguration: vi.fn().mockReturnValue({ dispose: vi.fn() }),
+  },
+  ThemeColor: class {
+    constructor(public id: string) {}
+  },
+  Uri: { file: vi.fn(), parse: vi.fn() },
+}));
+vi.mock("core/control-plane/env", () => ({ EXTENSION_NAME: "continue" }));
+vi.mock("../util/util", () => ({
+  getMetaKeyLabel: () => "Cmd",
+  getMetaKeyName: () => "metaKey",
+}));
+vi.mock("../util/getTheme", () => ({
+  getTheme: vi.fn().mockReturnValue({ colors: {} }),
+}));
+vi.mock("svg-builder", () => ({
+  default: { newInstance: () => ({ width: () => ({ height: () => ({}) }) }) },
+}));
+
+import { InlineTipManager } from "./InlineTipManager";
+
+describe("InlineTipManager.createSvgTooltipDecoration", () => {
+  it("does not throw when the active theme exposes no colors map", () => {
+    // A non-standard color theme can produce a Monaco theme whose `colors` is
+    // undefined. Previously the guard only checked `this.theme` was truthy and
+    // then read `this.theme.colors["editor.background"]`, throwing a TypeError
+    // that killed extension activation (issue #12947).
+    const instance = Object.create(InlineTipManager.prototype) as {
+      createSvgTooltipDecoration: () => unknown;
+      theme: unknown;
+    };
+    instance.theme = { colors: undefined };
+
+    expect(() => instance.createSvgTooltipDecoration()).not.toThrow();
+  });
+
+  it("uses the theme background when the colors map is present", () => {
+    const instance = Object.create(InlineTipManager.prototype) as {
+      createSvgTooltipDecoration: () => unknown;
+      theme: unknown;
+    };
+    instance.theme = { colors: { "editor.background": "#101010" } };
+
+    expect(() => instance.createSvgTooltipDecoration()).not.toThrow();
+  });
+});