diff --git a/packages/api/src/__tests__/assistant-tools-notification-create-errors.test.ts b/packages/api/src/__tests__/assistant-tools-notification-create-errors.test.ts
new file mode 100644
index 0000000..62eaf28
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-notification-create-errors.test.ts
@@ -0,0 +1,126 @@
+import { describe, expect, it, vi } from "vitest";
+import { SystemRole } from "@capakraken/shared";
+
+vi.mock("@capakraken/application", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@capakraken/application")>();
+  return {
+    ...actual,
+    getDashboardBudgetForecast: vi.fn().mockResolvedValue([]),
+    getDashboardPeakTimes: vi.fn().mockResolvedValue([]),
+    listAssignmentBookings: vi.fn().mockResolvedValue([]),
+  };
+});
+
+import { executeTool } from "../router/assistant-tools.js";
+import { createToolContext } from "./assistant-tools-notification-test-helpers.js";
+
+describe("assistant notification creation tools - errors", () => {
+  it("returns a stable assistant error when notification dueDate is invalid", async () => {
+    const ctx = createToolContext({}, SystemRole.MANAGER);
+
+    const result = await executeTool(
+      "create_notification",
+      JSON.stringify({
+        userId: "user_2",
+        type: "TASK_CREATED",
+        title: "Need review",
+        dueDate: "not-a-datetime",
+      }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Invalid dueDate: not-a-datetime",
+    });
+  });
+
+  it("returns a stable assistant error when notification recipient user is missing", async () => {
+    const ctx = createToolContext(
+      {
+        notification: {
+          create: vi.fn().mockRejectedValue({
+            code: "P2003",
+            message: "Foreign key constraint failed",
+            meta: { field_name: "Notification_userId_fkey" },
+          }),
+        },
+      },
+      SystemRole.MANAGER,
+    );
+
+    const result = await executeTool(
+      "create_notification",
+      JSON.stringify({
+        userId: "user_missing",
+        type: "TASK_CREATED",
+        title: "Need review",
+      }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Notification recipient user not found with the given criteria.",
+    });
+  });
+
+  it("returns a stable assistant error when notification assignee user is missing", async () => {
+    const ctx = createToolContext(
+      {
+        notification: {
+          create: vi.fn().mockRejectedValue({
+            code: "P2003",
+            message: "Foreign key constraint failed",
+            meta: { field_name: "Notification_assigneeId_fkey" },
+          }),
+        },
+      },
+      SystemRole.MANAGER,
+    );
+
+    const result = await executeTool(
+      "create_notification",
+      JSON.stringify({
+        userId: "user_2",
+        assigneeId: "user_missing",
+        type: "TASK_CREATED",
+        title: "Need review",
+        category: "TASK",
+      }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Assignee user not found with the given criteria.",
+    });
+  });
+
+  it("returns a stable assistant error when notification sender user is missing", async () => {
+    const ctx = createToolContext(
+      {
+        notification: {
+          create: vi.fn().mockRejectedValue({
+            code: "P2003",
+            message: "Foreign key constraint failed",
+            meta: { field_name: "Notification_senderId_fkey" },
+          }),
+        },
+      },
+      SystemRole.MANAGER,
+    );
+
+    const result = await executeTool(
+      "create_notification",
+      JSON.stringify({
+        userId: "user_2",
+        senderId: "user_missing",
+        type: "TASK_CREATED",
+        title: "Need review",
+      }),
+      ctx,
+    );
+
+    expect(JSON.parse(result.content)).toEqual({
+      error: "Sender user not found with the given criteria.",
+    });
+  });
+});
diff --git a/packages/api/src/__tests__/assistant-tools-notification-create-success.test.ts b/packages/api/src/__tests__/assistant-tools-notification-create-success.test.ts
new file mode 100644
index 0000000..9e51145
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-notification-create-success.test.ts
@@ -0,0 +1,121 @@
+import { describe, expect, it, vi } from "vitest";
+import { SystemRole } from "@capakraken/shared";
+
+vi.mock("@capakraken/application", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@capakraken/application")>();
+  return {
+    ...actual,
+    getDashboardBudgetForecast: vi.fn().mockResolvedValue([]),
+    getDashboardPeakTimes: vi.fn().mockResolvedValue([]),
+    listAssignmentBookings: vi.fn().mockResolvedValue([]),
+  };
+});
+
+import { executeTool } from "../router/assistant-tools.js";
+import { createToolContext } from "./assistant-tools-notification-test-helpers.js";
+
+describe("assistant notification creation tools - success", () => {
+  it("creates a notification through the notification router", async () => {
+    const db = {
+      notification: {
+        create: vi.fn().mockResolvedValue({ id: "notification_1", userId: "user_2" }),
+        findUnique: vi.fn().mockResolvedValue({
+          id: "notification_1",
+          title: "Need review",
+          userId: "user_2",
+          category: "TASK",
+        }),
+      },
+      user: {
+        findUnique: vi.fn().mockResolvedValue({ id: "user_2", email: "user2@example.com", name: "User Two" }),
+      },
+    };
+    const ctx = createToolContext(db, SystemRole.ADMIN);
+
+    const result = await executeTool(
+      "create_notification",
+      JSON.stringify({
+        userId: "user_2",
+        type: "TASK_CREATED",
+        title: "Need review",
+        category: "TASK",
+        taskStatus: "OPEN",
+        dueDate: "2026-04-02T09:30:00.000Z",
+        channel: "in_app",
+      }),
+      ctx,
+    );
+
+    expect(db.notification.create).toHaveBeenCalledWith({
+      data: expect.objectContaining({
+        userId: "user_2",
+        type: "TASK_CREATED",
+        title: "Need review",
+        category: "TASK",
+        taskStatus: "OPEN",
+        dueDate: new Date("2026-04-02T09:30:00.000Z"),
+        senderId: "user_1",
+        channel: "in_app",
+      }),
+    });
+    expect(db.notification.findUnique).toHaveBeenCalledWith({
+      where: { id: "notification_1" },
+    });
+    expect(JSON.parse(result.content)).toEqual(
+      expect.objectContaining({
+        success: true,
+        notificationId: "notification_1",
+        message: 'Created notification "Need review".',
+      }),
+    );
+    expect(result.action).toEqual({
+      type: "invalidate",
+      scope: ["notification"],
+    });
+  });
+
+  it("defaults task-like notifications to OPEN when the caller omits taskStatus", async () => {
+    const db = {
+      notification: {
+        create: vi.fn().mockResolvedValue({ id: "notification_2", userId: "user_2" }),
+        findUnique: vi.fn().mockResolvedValue({
+          id: "notification_2",
+          title: "Need review",
+          userId: "user_2",
+          category: "TASK",
+          taskStatus: "OPEN",
+        }),
+      },
+      user: {
+        findUnique: vi.fn().mockResolvedValue({ id: "user_2", email: "user2@example.com", name: "User Two" }),
+      },
+    };
+    const ctx = createToolContext(db, SystemRole.ADMIN);
+
+    const result = await executeTool(
+      "create_notification",
+      JSON.stringify({
+        userId: "user_2",
+        type: "TASK_CREATED",
+        title: "Need review",
+        category: "TASK",
+        channel: "in_app",
+      }),
+      ctx,
+    );
+
+    expect(db.notification.create).toHaveBeenCalledWith({
+      data: expect.objectContaining({
+        userId: "user_2",
+        category: "TASK",
+        taskStatus: "OPEN",
+      }),
+    });
+    expect(JSON.parse(result.content)).toEqual(
+      expect.objectContaining({
+        success: true,
+        notificationId: "notification_2",
+      }),
+    );
+  });
+});
diff --git a/packages/api/src/__tests__/assistant-tools-notification-inbox-mutations.test.ts b/packages/api/src/__tests__/assistant-tools-notification-inbox-mutations.test.ts
new file mode 100644
index 0000000..604adb6
--- /dev/null
+++ b/packages/api/src/__tests__/assistant-tools-notification-inbox-mutations.test.ts
@@ -0,0 +1,71 @@
+import { describe, expect, it, vi } from "vitest";
+import { SystemRole } from "@capakraken/shared";
+
+vi.mock("@capakraken/application", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@capakraken/application")>();
+  return {
+    ...actual,
+    getDashboardBudgetForecast: vi.fn().mockResolvedValue([]),
+    getDashboardPeakTimes: vi.fn().mockResolvedValue([]),
+    listAssignmentBookings: vi.fn().mockResolvedValue([]),
+  };
+});
+
+import { executeTool } from "../router/assistant-tools.js";
+import { createToolContext, withUserLookup } from "./assistant-tools-notification-test-helpers.js";
+
+describe("assistant notification inbox mutation tools", () => {
+  it("marks all unread notifications as read through the notification router", async () => {
+    const db = {
+      user: {
+        findUnique: vi.fn().mockResolvedValue({ id: "user_1" }),
+      },
+      notification: {
+        updateMany: vi.fn().mockResolvedValue({ count: 3 }),
+      },
+    };
+    const ctx = createToolContext(db, SystemRole.CONTROLLER);
+
+    const result = await executeTool("mark_notification_read", "{}", ctx);
+
+    expect(db.notification.updateMany).toHaveBeenCalledWith({
+      where: { userId: "user_1", readAt: null },
+      data: { readAt: expect.any(Date) },
+    });
+    expect(JSON.parse(result.content)).toEqual(
+      expect.objectContaining({
+        success: true,
+        message: "All unread notifications marked as read.",
+      }),
+    );
+  });
+
+  it("deletes notifications through the router and invalidates notification queries", async () => {
+    const db = withUserLookup({
+      notification: {
+        findFirst: vi.fn().mockResolvedValue({
+          id: "notif_9",
+          userId: "user_1",
+          category: "NOTIFICATION",
+          senderId: "user_mgr",
+        }),
+        delete: vi.fn().mockResolvedValue({ id: "notif_9" }),
+      },
+    });
+    const ctx = createToolContext(db, SystemRole.USER);
+
+    const result = await executeTool(
+      "delete_notification",
+      JSON.stringify({ id: "notif_9" }),
+      ctx,
+    );
+
+    expect(db.notification.delete).toHaveBeenCalledWith({ where: { id: "notif_9" } });
+    expect(result.action).toEqual({ type: "invalidate", scope: ["notification"] });
+    expect(result.data).toEqual({
+      success: true,
+      id: "notif_9",
+      message: "Deleted notification notif_9.",
+    });
+  });
+});