diff --git a/package.json b/package.json
index 6b28eaa2d..1ecab8cb9 100644
--- a/package.json
+++ b/package.json
@@ -32,7 +32,8 @@
     "test:core": "bun packages/scripts/src/testing/run.ts core",
     "test:web": "bun packages/scripts/src/testing/run.ts web",
     "test:scripts": "bun packages/scripts/src/testing/run.ts scripts",
-    "type-check": "bunx typescript@6.0.3 --noEmit && bunx typescript@6.0.3 -p packages/web/tsconfig.app.json --noEmit",
+    "type-check": "bunx typescript@6.0.3 --noEmit && bunx typescript@6.0.3 -p packages/web/tsconfig.app.json --noEmit && bun run type-check:web-tests",
+    "type-check:web-tests": "bunx typescript@6.0.3 -p packages/web/tsconfig.test.json --noEmit",
     "verify": "bun packages/scripts/src/testing/verify.ts",
     "build:backend": "bun packages/scripts/src/commands/build.backend.ts",
     "build:web": "cd packages/web && bun --env-file=../backend/.env.local run build.ts"
diff --git a/packages/web/src/__tests__/patched-jest.d.ts b/packages/web/src/__tests__/patched-jest.d.ts
index 6ba2a6a7c..f2839a9be 100644
--- a/packages/web/src/__tests__/patched-jest.d.ts
+++ b/packages/web/src/__tests__/patched-jest.d.ts
@@ -1,3 +1,9 @@
 import type { jest as JestNamespace } from "bun:test";
+import type { TestingLibraryMatchers } from "@types/testing-library__jest-dom/matchers";
 
 export declare const jest: typeof JestNamespace;
+
+declare module "bun:test" {
+  interface Matchers<T = unknown>
+    extends TestingLibraryMatchers<unknown, void> {}
+}
diff --git a/packages/web/src/common/apis/base/base.api.test.ts b/packages/web/src/common/apis/base/base.api.test.ts
index cbee1585c..ae982afd9 100644
--- a/packages/web/src/common/apis/base/base.api.test.ts
+++ b/packages/web/src/common/apis/base/base.api.test.ts
@@ -23,7 +23,7 @@ describe("BaseApi backend availability", () => {
   it("marks the backend unavailable when fetch cannot reach it", async () => {
     globalThis.fetch = mock(() =>
       Promise.reject(new TypeError("Failed to fetch")),
-    ) as typeof fetch;
+    ) as unknown as typeof fetch;
 
     await expect(BaseApi.get("/event")).rejects.toMatchObject({
       name: "ApiError",
@@ -36,7 +36,7 @@ describe("BaseApi backend availability", () => {
     markBackendUnavailable();
     globalThis.fetch = mock(() =>
       Promise.resolve(new Response("{}", { status: 200 })),
-    ) as typeof fetch;
+    ) as unknown as typeof fetch;
 
     await BaseApi.get("/config");
 
diff --git a/packages/web/src/common/apis/util/api.util.test.ts b/packages/web/src/common/apis/util/api.util.test.ts
index 159984522..52aedc5ba 100644
--- a/packages/web/src/common/apis/util/api.util.test.ts
+++ b/packages/web/src/common/apis/util/api.util.test.ts
@@ -2,7 +2,7 @@ import {
   ApiErrorResponseSchema,
   GoogleConnectErrorResponseSchema,
 } from "@core/types/auth.types";
-import { type ApiError } from "../api.types";
+import { type ApiError, type ApiResponse } from "../api.types";
 import {
   getApiErrorCode,
   parseApiError,
diff --git a/packages/web/src/common/hooks/useBufferedVisibility.test.ts b/packages/web/src/common/hooks/useBufferedVisibility.test.ts
index 961b2adb2..42206c7b4 100644
--- a/packages/web/src/common/hooks/useBufferedVisibility.test.ts
+++ b/packages/web/src/common/hooks/useBufferedVisibility.test.ts
@@ -32,10 +32,13 @@ describe("useBufferedVisibility", () => {
     ) => {
       const id = ++currentTimeoutId;
       if (typeof callback === "function") {
-        activeTimeouts.set(id, { callback, delay: delay ?? 0 });
+        activeTimeouts.set(id, {
+          callback: () => callback(),
+          delay: delay ?? 0,
+        });
       }
       return id;
-    }) as typeof setTimeout);
+    }) as unknown as typeof setTimeout);
 
     clearTimeoutSpy = spyOn(globalThis, "clearTimeout").mockImplementation(((
       id?: number,
@@ -43,7 +46,7 @@ describe("useBufferedVisibility", () => {
       if (id !== undefined) {
         activeTimeouts.delete(id);
       }
-    }) as typeof clearTimeout);
+    }) as unknown as typeof clearTimeout);
   });
 
   afterEach(() => {
diff --git a/packages/web/src/common/hooks/useEventDNDActions.test.ts b/packages/web/src/common/hooks/useEventDNDActions.test.ts
index ca502df18..4b9d02fb3 100644
--- a/packages/web/src/common/hooks/useEventDNDActions.test.ts
+++ b/packages/web/src/common/hooks/useEventDNDActions.test.ts
@@ -1,8 +1,8 @@
 import { type DragEndEvent } from "@dnd-kit/core";
 import { renderHook } from "@testing-library/react";
 import { BehaviorSubject } from "rxjs";
-import { Categories_Event } from "@core/types/event.types";
-import dayjs from "@core/util/date/dayjs";
+import { Categories_Event, type Schema_Event } from "@core/types/event.types";
+import dayjs, { type Dayjs } from "@core/util/date/dayjs";
 import {
   ID_GRID_ALLDAY_ROW,
   ID_GRID_MAIN,
@@ -41,16 +41,18 @@ mock.module("@web/views/Day/util/agenda/agenda.util", () => ({
   // Provide a focused mock that includes the named export consumers expect.
   // Keep a safe default for other exports so concurrent tests won't break imports.
   getSnappedMinutes: mockGetSnappedMinutes,
-  getAgendaEventTitle: (event) => `${event?.title || ""} -`,
-  getAgendaEventTime: (d) => (d ? new Date(d).toISOString() : ""),
-  getAgendaEventPosition: (_date) => 0,
-  getNowLinePosition: (_date) => 0,
-  getEventTimeFromPosition: (_y, dateInView) =>
-    dateInView.startOf ? dateInView.startOf("day") : new Date(),
-  roundMinutesToNearestFifteen: (minutes) => Math.round(minutes / 15) * 15,
-  roundToNearestFifteenWithinHour: (minutes) =>
+  getAgendaEventTitle: (event: Schema_Event) => `${event.title ?? ""} -`,
+  getAgendaEventTime: (date: Date | string) =>
+    date ? new Date(date).toISOString() : "",
+  getAgendaEventPosition: (_date: Date) => 0,
+  getNowLinePosition: (_date: Date) => 0,
+  getEventTimeFromPosition: (_y: number, dateInView: Dayjs) =>
+    dateInView.startOf("day"),
+  roundMinutesToNearestFifteen: (minutes: number) =>
+    Math.round(minutes / 15) * 15,
+  roundToNearestFifteenWithinHour: (minutes: number) =>
     Math.min(45, Math.round(minutes / 15) * 15),
-  getEventHeight: (_event) => 4,
+  getEventHeight: (_event: Pick<Schema_Event, "startDate" | "endDate">) => 4,
 }));
 
 mock.module("@web/ducks/events/selectors/event.selectors", () => ({
diff --git a/packages/web/src/common/hooks/useMainGridSelectionState.test.ts b/packages/web/src/common/hooks/useMainGridSelectionState.test.ts
index b19bf0f9e..82dd63074 100644
--- a/packages/web/src/common/hooks/useMainGridSelectionState.test.ts
+++ b/packages/web/src/common/hooks/useMainGridSelectionState.test.ts
@@ -16,10 +16,10 @@ describe("useMainGridSelectionState", () => {
       callback: TimerHandler,
     ) => {
       if (typeof callback === "function") {
-        timeoutCallback = callback;
+        timeoutCallback = () => callback();
       }
       return 1;
-    }) as typeof setTimeout);
+    }) as unknown as typeof setTimeout);
 
     act(() => {
       selecting$.next(false);
diff --git a/packages/web/src/common/hooks/useOpenAtCursor.test.ts b/packages/web/src/common/hooks/useOpenAtCursor.test.ts
index a60a067cd..0ce037bf2 100644
--- a/packages/web/src/common/hooks/useOpenAtCursor.test.ts
+++ b/packages/web/src/common/hooks/useOpenAtCursor.test.ts
@@ -34,10 +34,10 @@ describe("useOpenAtCursor", () => {
       callback: TimerHandler,
     ) => {
       if (typeof callback === "function") {
-        timeoutCallbacks.push(callback);
+        timeoutCallbacks.push(() => callback());
       }
       return timeoutCallbacks.length;
-    }) as typeof setTimeout);
+    }) as unknown as typeof setTimeout);
 
     // Reset state before each test
     open$.next(false);
diff --git a/packages/web/src/common/hooks/useVersionCheck.test.ts b/packages/web/src/common/hooks/useVersionCheck.test.ts
index aa63a404c..692c2a24f 100644
--- a/packages/web/src/common/hooks/useVersionCheck.test.ts
+++ b/packages/web/src/common/hooks/useVersionCheck.test.ts
@@ -71,7 +71,7 @@ describe("useVersionCheck", () => {
       ok: true,
       json: async () => ({ version: "dev" }),
     });
-    global.fetch = fetchMock as typeof fetch;
+    global.fetch = fetchMock as unknown as typeof fetch;
   });
 
   afterEach(() => {
diff --git a/packages/web/src/common/repositories/event/remote.event.repository.test.ts b/packages/web/src/common/repositories/event/remote.event.repository.test.ts
index a71d1bb5e..3f0d6526b 100644
--- a/packages/web/src/common/repositories/event/remote.event.repository.test.ts
+++ b/packages/web/src/common/repositories/event/remote.event.repository.test.ts
@@ -37,6 +37,7 @@ mock.module("@web/common/storage/adapter/adapter", () => ({
 
 const { RemoteEventRepository } =
   require("./remote.event.repository") as typeof import("./remote.event.repository");
+type RemoteEventRepositoryInstance = InstanceType<typeof RemoteEventRepository>;
 
 function createBackendUnavailableError(): Error {
   const error = new Error("Request failed");
@@ -45,7 +46,7 @@ function createBackendUnavailableError(): Error {
 }
 
 describe("RemoteEventRepository", () => {
-  let repository: RemoteEventRepository;
+  let repository: RemoteEventRepositoryInstance;
 
   beforeEach(() => {
     mockCreate.mockClear();
diff --git a/packages/web/src/common/storage/migrations/data/task-id-to-underscore-id.test.ts b/packages/web/src/common/storage/migrations/data/task-id-to-underscore-id.test.ts
index 425e7ba14..e8edeee84 100644
--- a/packages/web/src/common/storage/migrations/data/task-id-to-underscore-id.test.ts
+++ b/packages/web/src/common/storage/migrations/data/task-id-to-underscore-id.test.ts
@@ -26,7 +26,6 @@ function createMockAdapter(): MockedStorageAdapter {
     clearAllEvents: mock().mockResolvedValue(undefined),
     getMigrationRecords: mock().mockResolvedValue([]),
     setMigrationRecord: mock().mockResolvedValue(undefined),
-    close: mock(),
   };
 }
 
diff --git a/packages/web/src/common/storage/migrations/external/demo-data-seed.test.ts b/packages/web/src/common/storage/migrations/external/demo-data-seed.test.ts
index 0aa7acc3e..77696a8de 100644
--- a/packages/web/src/common/storage/migrations/external/demo-data-seed.test.ts
+++ b/packages/web/src/common/storage/migrations/external/demo-data-seed.test.ts
@@ -12,6 +12,7 @@ import { createMockStorageAdapter } from "@web/__tests__/utils/storage/mock-stor
 import {
   GridEventSchema,
   type Schema_GridEvent,
+  type Schema_WebEvent,
 } from "@web/common/types/web.event.types";
 import { demoDataSeedMigration } from "./demo-data-seed";
 import { afterEach, beforeEach, describe, expect, it, spyOn } from "bun:test";
@@ -48,7 +49,7 @@ describe("demoDataSeedMigration", () => {
     expect(adapter.putTasks).toHaveBeenCalled();
 
     // Verify events were created (7 total: 5 today + 2 someday)
-    const eventsCall = adapter.putEvents.mock.calls[0][0];
+    const eventsCall = adapter.putEvents.mock.calls[0][0] as Schema_WebEvent[];
     expect(eventsCall).toHaveLength(7);
 
     // Verify tasks were created for 3 days
@@ -91,7 +92,7 @@ describe("demoDataSeedMigration", () => {
 
     await demoDataSeedMigration.migrate(adapter);
 
-    const eventsCall = adapter.putEvents.mock.calls[0][0];
+    const eventsCall = adapter.putEvents.mock.calls[0][0] as Schema_WebEvent[];
     const today = dayjs().toYearMonthDayString();
 
     // Check that at least one timed event starts today
@@ -110,7 +111,9 @@ describe("demoDataSeedMigration", () => {
     const yesterday = dayjs().subtract(1, "day").toYearMonthDayString();
     const tomorrow = dayjs().add(1, "day").toYearMonthDayString();
 
-    const putTasksCalls = adapter.putTasks.mock.calls;
+    const putTasksCalls = adapter.putTasks.mock.calls as Array<
+      [string, ReturnType<typeof createMockTask>[]]
+    >;
     const dateKeys = putTasksCalls.map((call) => call[0]);
 
     expect(dateKeys).toContain(today);
@@ -124,11 +127,15 @@ describe("demoDataSeedMigration", () => {
     await demoDataSeedMigration.migrate(adapter);
 
     const yesterday = dayjs().subtract(1, "day").toYearMonthDayString();
-    const putTasksCalls = adapter.putTasks.mock.calls;
+    const putTasksCalls = adapter.putTasks.mock.calls as Array<
+      [string, ReturnType<typeof createMockTask>[]]
+    >;
     const yesterdayCall = putTasksCalls.find((call) => call[0] === yesterday);
 
-    expect(yesterdayCall).toBeDefined();
-    const yesterdayTasks = yesterdayCall![1];
+    if (!yesterdayCall) {
+      throw new Error("Expected yesterday tasks to be seeded");
+    }
+    const yesterdayTasks = yesterdayCall[1];
     expect(yesterdayTasks.every((t) => t.status === "completed")).toBe(true);
   });
 
@@ -137,7 +144,7 @@ describe("demoDataSeedMigration", () => {
 
     await demoDataSeedMigration.migrate(adapter);
 
-    const eventsCall = adapter.putEvents.mock.calls[0][0];
+    const eventsCall = adapter.putEvents.mock.calls[0][0] as Schema_WebEvent[];
     const priorities = new Set(eventsCall.map((e) => e.priority));
 
     expect(priorities.has(Priorities.WORK)).toBe(true);
@@ -151,7 +158,7 @@ describe("demoDataSeedMigration", () => {
 
     await demoDataSeedMigration.migrate(adapter);
 
-    const eventsCall = adapter.putEvents.mock.calls[0][0];
+    const eventsCall = adapter.putEvents.mock.calls[0][0] as Schema_WebEvent[];
     const somedayEvents = eventsCall.filter((e) => e.isSomeday);
 
     expect(somedayEvents).toHaveLength(2);
@@ -162,7 +169,7 @@ describe("demoDataSeedMigration", () => {
 
     await demoDataSeedMigration.migrate(adapter);
 
-    const eventsCall = adapter.putEvents.mock.calls[0][0];
+    const eventsCall = adapter.putEvents.mock.calls[0][0] as Schema_WebEvent[];
     const allDayEvents = eventsCall.filter((e) => e.isAllDay);
 
     expect(allDayEvents).toHaveLength(1);
@@ -174,7 +181,7 @@ describe("demoDataSeedMigration", () => {
 
     await demoDataSeedMigration.migrate(adapter);
 
-    const eventsCall = adapter.putEvents.mock.calls[0][0];
+    const eventsCall = adapter.putEvents.mock.calls[0][0] as Schema_WebEvent[];
     const timedEvents = eventsCall.filter((e) => !e.isSomeday && !e.isAllDay);
 
     // RFC3339 offset format: "2026-02-19T16:30:00-08:00" (no milliseconds, offset instead of Z)
@@ -193,7 +200,7 @@ describe("demoDataSeedMigration", () => {
 
     await demoDataSeedMigration.migrate(adapter);
 
-    const eventsCall = adapter.putEvents.mock.calls[0][0];
+    const eventsCall = adapter.putEvents.mock.calls[0][0] as Schema_WebEvent[];
     const timedEvents = eventsCall.filter(
       (e) => !e.isSomeday && !e.isAllDay,
     ) as Schema_GridEvent[];
@@ -219,7 +226,7 @@ describe("demoDataSeedMigration", () => {
 
     await demoDataSeedMigration.migrate(adapter);
 
-    const eventsCall = adapter.putEvents.mock.calls[0][0];
+    const eventsCall = adapter.putEvents.mock.calls[0][0] as Schema_WebEvent[];
 
     for (const event of eventsCall) {
       if (!event.isSomeday && !event.isAllDay) {
diff --git a/packages/web/src/common/storage/migrations/external/localstorage-tasks.test.ts b/packages/web/src/common/storage/migrations/external/localstorage-tasks.test.ts
index e205474c3..88339f981 100644
--- a/packages/web/src/common/storage/migrations/external/localstorage-tasks.test.ts
+++ b/packages/web/src/common/storage/migrations/external/localstorage-tasks.test.ts
@@ -54,7 +54,6 @@ function createMockAdapter(): MockedStorageAdapter {
     clearAllEvents: mock().mockResolvedValue(undefined),
     getMigrationRecords: mock().mockResolvedValue([]),
     setMigrationRecord: mock().mockResolvedValue(undefined),
-    close: mock(),
   };
 }
 
@@ -199,6 +198,7 @@ describe("localStorageTasksMigration", () => {
 
     expect(localStorage.getItem(validKey)).toBeNull();
     expect(localStorage.getItem(invalidKey)).toBe("invalid json {{{");
+    consoleErrorSpy.mockRestore();
   });
 
   it("skips non-array parsed values and does not remove key", async () => {
diff --git a/packages/web/src/common/utils/app-init.util.test.ts b/packages/web/src/common/utils/app-init.util.test.ts
index d780e59c7..84e207ca7 100644
--- a/packages/web/src/common/utils/app-init.util.test.ts
+++ b/packages/web/src/common/utils/app-init.util.test.ts
@@ -44,7 +44,7 @@ describe("app-init.util", () => {
         timeoutCallback = () => callback();
       }
       return timeoutId;
-    }) as typeof setTimeout);
+    }) as unknown as typeof setTimeout);
   });
 
   afterEach(() => {
diff --git a/packages/web/src/common/utils/dom/event-emitter.util.test.ts b/packages/web/src/common/utils/dom/event-emitter.util.test.ts
index 174a19eaa..c920078fc 100644
--- a/packages/web/src/common/utils/dom/event-emitter.util.test.ts
+++ b/packages/web/src/common/utils/dom/event-emitter.util.test.ts
@@ -35,7 +35,7 @@ describe("event-emitter.util", () => {
           expect(val.x).toBe(100);
           expect(val.y).toBe(100);
           expect(val.element).toBe(mockElement);
-          expect(val.event).toBe(event);
+          expect(val.event as unknown).toBe(event);
           subscription.unsubscribe();
           resolve();
         });
diff --git a/packages/web/src/common/utils/dom/event-target-visibility.util.test.ts b/packages/web/src/common/utils/dom/event-target-visibility.util.test.ts
index 47797317e..cea3e954b 100644
--- a/packages/web/src/common/utils/dom/event-target-visibility.util.test.ts
+++ b/packages/web/src/common/utils/dom/event-target-visibility.util.test.ts
@@ -7,7 +7,8 @@ const mockIntersectionObserver = mock();
 const mockObserve = mock();
 const mockDisconnect = mock();
 
-global.IntersectionObserver = mockIntersectionObserver;
+global.IntersectionObserver =
+  mockIntersectionObserver as unknown as typeof IntersectionObserver;
 
 describe("onEventTargetVisibility", () => {
   beforeEach(() => {
@@ -40,7 +41,9 @@ describe("onEventTargetVisibility", () => {
       currentTarget: document.createElement("div"),
     } as SyntheticEvent<HTMLDivElement>;
 
-    let observerCallback: (entries: IntersectionObserverEntry[]) => void;
+    let observerCallback:
+      | ((entries: IntersectionObserverEntry[]) => void)
+      | undefined;
 
     mockIntersectionObserver.mockImplementation((callback) => {
       observerCallback = callback;
@@ -53,8 +56,11 @@ describe("onEventTargetVisibility", () => {
     const eventHandler = onEventTargetVisibility(mockCallback, true);
     eventHandler(mockEvent);
 
+    if (!observerCallback) {
+      throw new Error("Expected IntersectionObserver callback");
+    }
     // Simulate intersection observer callback with isIntersecting = true
-    observerCallback!([{ isIntersecting: true } as IntersectionObserverEntry]);
+    observerCallback([{ isIntersecting: true } as IntersectionObserverEntry]);
 
     expect(mockCallback).toHaveBeenCalledTimes(1);
     expect(mockDisconnect).toHaveBeenCalledTimes(1);
@@ -66,7 +72,9 @@ describe("onEventTargetVisibility", () => {
       currentTarget: document.createElement("div"),
     } as SyntheticEvent<HTMLDivElement>;
 
-    let observerCallback: (entries: IntersectionObserverEntry[]) => void;
+    let observerCallback:
+      | ((entries: IntersectionObserverEntry[]) => void)
+      | undefined;
 
     mockIntersectionObserver.mockImplementation((callback) => {
       observerCallback = callback;
@@ -79,8 +87,11 @@ describe("onEventTargetVisibility", () => {
     const eventHandler = onEventTargetVisibility(mockCallback, false);
     eventHandler(mockEvent);
 
+    if (!observerCallback) {
+      throw new Error("Expected IntersectionObserver callback");
+    }
     // Simulate intersection observer callback with isIntersecting = false
-    observerCallback!([{ isIntersecting: false } as IntersectionObserverEntry]);
+    observerCallback([{ isIntersecting: false } as IntersectionObserverEntry]);
 
     expect(mockCallback).toHaveBeenCalledTimes(1);
     expect(mockDisconnect).toHaveBeenCalledTimes(1);
@@ -92,7 +103,9 @@ describe("onEventTargetVisibility", () => {
       currentTarget: document.createElement("div"),
     } as SyntheticEvent<HTMLDivElement>;
 
-    let observerCallback: (entries: IntersectionObserverEntry[]) => void;
+    let observerCallback:
+      | ((entries: IntersectionObserverEntry[]) => void)
+      | undefined;
 
     mockIntersectionObserver.mockImplementation((callback) => {
       observerCallback = callback;
@@ -105,8 +118,11 @@ describe("onEventTargetVisibility", () => {
     const eventHandler = onEventTargetVisibility(mockCallback, true);
     eventHandler(mockEvent);
 
+    if (!observerCallback) {
+      throw new Error("Expected IntersectionObserver callback");
+    }
     // Simulate intersection observer callback with isIntersecting = false (doesn't match expected true)
-    observerCallback!([{ isIntersecting: false } as IntersectionObserverEntry]);
+    observerCallback([{ isIntersecting: false } as IntersectionObserverEntry]);
 
     expect(mockCallback).not.toHaveBeenCalled();
     expect(mockDisconnect).not.toHaveBeenCalled();
@@ -118,7 +134,9 @@ describe("onEventTargetVisibility", () => {
       currentTarget: document.createElement("div"),
     } as SyntheticEvent<HTMLDivElement>;
 
-    let observerCallback: (entries: IntersectionObserverEntry[]) => void;
+    let observerCallback:
+      | ((entries: IntersectionObserverEntry[]) => void)
+      | undefined;
 
     mockIntersectionObserver.mockImplementation((callback) => {
       observerCallback = callback;
@@ -131,8 +149,11 @@ describe("onEventTargetVisibility", () => {
     const eventHandler = onEventTargetVisibility(mockCallback);
     eventHandler(mockEvent);
 
+    if (!observerCallback) {
+      throw new Error("Expected IntersectionObserver callback");
+    }
     // Simulate intersection observer callback with isIntersecting = false (matches default)
-    observerCallback!([{ isIntersecting: false } as IntersectionObserverEntry]);
+    observerCallback([{ isIntersecting: false } as IntersectionObserverEntry]);
 
     expect(mockCallback).toHaveBeenCalledTimes(1);
     expect(mockDisconnect).toHaveBeenCalledTimes(1);
@@ -144,7 +165,9 @@ describe("onEventTargetVisibility", () => {
       currentTarget: document.createElement("div"),
     } as SyntheticEvent<HTMLDivElement>;
 
-    let observerCallback: (entries: IntersectionObserverEntry[]) => void;
+    let observerCallback:
+      | ((entries: IntersectionObserverEntry[]) => void)
+      | undefined;
 
     mockIntersectionObserver.mockImplementation((callback) => {
       observerCallback = callback;
@@ -157,8 +180,11 @@ describe("onEventTargetVisibility", () => {
     const eventHandler = onEventTargetVisibility(mockCallback, true);
     eventHandler(mockEvent);
 
+    if (!observerCallback) {
+      throw new Error("Expected IntersectionObserver callback");
+    }
     // Simulate intersection observer callback with multiple entries
-    observerCallback!([
+    observerCallback([
       { isIntersecting: true } as IntersectionObserverEntry,
       { isIntersecting: false } as IntersectionObserverEntry,
     ]);
diff --git a/packages/web/src/common/utils/event/event.util.test.ts b/packages/web/src/common/utils/event/event.util.test.ts
index 1a186e465..200b01744 100644
--- a/packages/web/src/common/utils/event/event.util.test.ts
+++ b/packages/web/src/common/utils/event/event.util.test.ts
@@ -67,8 +67,9 @@ describe("_assembleGridEvent", () => {
   it("should successfully convert Someday event to Grid event by adding position field", () => {
     // Create a mock Someday event (without position field)
     const somedayEvent = createMockStandaloneEvent({
+      _id: new ObjectId().toString(),
       isSomeday: true,
-    }) as Schema_WebEvent;
+    }) as Schema_WebEvent & { _id: string };
 
     const generator = _assembleGridEvent(somedayEvent);
 
@@ -93,7 +94,10 @@ describe("_assembleGridEvent", () => {
 
 describe("addId", () => {
   it("should add a raw MongoID", () => {
-    const event = createMockStandaloneEvent() as Schema_GridEvent;
+    const event = {
+      ...createMockStandaloneEvent(),
+      _id: "existing-id",
+    } as Schema_GridEvent;
     const result = addId(event);
 
     expect(result._id).toBeDefined();
diff --git a/packages/web/src/common/utils/grid/assign.row.test.ts b/packages/web/src/common/utils/grid/assign.row.test.ts
index cdf388711..d7c175d97 100644
--- a/packages/web/src/common/utils/grid/assign.row.test.ts
+++ b/packages/web/src/common/utils/grid/assign.row.test.ts
@@ -116,7 +116,9 @@ describe("case: 10 multi-week events with identical times", () => {
 });
 
 describe("case: March 13-19", () => {
-  const { rowsCount, allDayEvents } = assignEventsToRow(mar13To19);
+  const { rowsCount, allDayEvents } = assignEventsToRow(
+    mar13To19 as Parameters<typeof assignEventsToRow>[0],
+  );
   it("uses 5 rows", () => {
     expect(rowsCount).toBe(5);
   });
diff --git a/packages/web/src/common/validators/grid.event.validator.test.ts b/packages/web/src/common/validators/grid.event.validator.test.ts
index 23090aa8c..ef4c39403 100644
--- a/packages/web/src/common/validators/grid.event.validator.test.ts
+++ b/packages/web/src/common/validators/grid.event.validator.test.ts
@@ -73,6 +73,6 @@ describe("validateGridEvent", () => {
       },
     };
 
-    expect(() => validateGridEvent(event)).toThrow();
+    expect(() => validateGridEvent(event as Schema_GridEvent)).toThrow();
   });
 });
diff --git a/packages/web/src/components/DND/DNDContext.test.tsx b/packages/web/src/components/DND/DNDContext.test.tsx
index 7a65fc180..76cebae8e 100644
--- a/packages/web/src/components/DND/DNDContext.test.tsx
+++ b/packages/web/src/components/DND/DNDContext.test.tsx
@@ -10,7 +10,14 @@ import {
   spyOn,
 } from "bun:test";
 
-const DndContext = mock(({ children }: { children: ReactNode }) => (
+type MockDndContextProps = {
+  children: ReactNode;
+  onDragAbort: () => void;
+  onDragCancel: () => void;
+  onDragEnd: () => void;
+};
+
+const DndContext = mock(({ children }: MockDndContextProps) => (
   <div data-testid="dnd-context">{children}</div>
 ));
 const usePointerPosition = mock();
diff --git a/packages/web/src/components/HeaderInfoIcon/HeaderInfoIcon.test.tsx b/packages/web/src/components/HeaderInfoIcon/HeaderInfoIcon.test.tsx
index 4accd07ed..2c6780cef 100644
--- a/packages/web/src/components/HeaderInfoIcon/HeaderInfoIcon.test.tsx
+++ b/packages/web/src/components/HeaderInfoIcon/HeaderInfoIcon.test.tsx
@@ -46,7 +46,7 @@ const mockUseConnectGoogle = mock(
   }),
 );
 const mockShouldShowAnonymousCalendarChangeSignUpPrompt = mock(() => false);
-const mockSubscribeToAuthState = mock(() => () => {});
+const mockSubscribeToAuthState = mock((_listener: () => void) => () => {});
 const mockClearAnonymousCalendarChangeSignUpPrompt = mock();
 const mockClearAuthenticationState = mock();
 const mockGetAuthState = mock();
diff --git a/packages/web/src/components/SyncEventsOverlay/SyncEventsOverlay.test.tsx b/packages/web/src/components/SyncEventsOverlay/SyncEventsOverlay.test.tsx
index edb89ea0c..0d5c36c52 100644
--- a/packages/web/src/components/SyncEventsOverlay/SyncEventsOverlay.test.tsx
+++ b/packages/web/src/components/SyncEventsOverlay/SyncEventsOverlay.test.tsx
@@ -89,10 +89,10 @@ describe("SyncEventsOverlay", () => {
       if (typeof callback === "function") {
         pendingTimers.push(() => callback());
       }
-      return 1 as ReturnType<typeof setTimeout>;
-    }) as typeof setTimeout);
+      return 1;
+    }) as unknown as typeof setTimeout);
     clearTimeoutSpy = spyOn(globalThis, "clearTimeout").mockImplementation(
-      (() => undefined) as typeof clearTimeout,
+      (() => undefined) as unknown as typeof clearTimeout,
     );
     document.body.removeAttribute("data-app-locked");
   });
diff --git a/packages/web/src/ducks/events/sagas/event.sagas.prompt.test.ts b/packages/web/src/ducks/events/sagas/event.sagas.prompt.test.ts
index 03dfb6b2f..5331420cc 100644
--- a/packages/web/src/ducks/events/sagas/event.sagas.prompt.test.ts
+++ b/packages/web/src/ducks/events/sagas/event.sagas.prompt.test.ts
@@ -38,9 +38,10 @@ const { createEvent, editEvent } =
   require("./event.sagas") as typeof import("./event.sagas");
 
 describe("event sign-up prompt failure paths", () => {
+  const mockEventId = "event-1";
   const mockEvent = {
     ...createMockStandaloneEvent(),
-    _id: "event-1",
+    _id: mockEventId,
     isSomeday: false,
   } as Schema_Event;
 
@@ -106,7 +107,7 @@ describe("event sign-up prompt failure paths", () => {
           events: {
             entities: {
               value: {
-                [mockEvent._id]: mockEvent,
+                [mockEventId]: mockEvent,
               },
             },
             pendingEvents: { eventIds: [] },
diff --git a/packages/web/src/ducks/events/sagas/event.sagas.test.ts b/packages/web/src/ducks/events/sagas/event.sagas.test.ts
index a1771cb65..0b406e3ca 100644
--- a/packages/web/src/ducks/events/sagas/event.sagas.test.ts
+++ b/packages/web/src/ducks/events/sagas/event.sagas.test.ts
@@ -244,7 +244,7 @@ describe("createEvent saga - optimistic rendering", () => {
 
   it("should keep event in state during API call", async () => {
     // Create a promise that we can control
-    let resolveApiCall: (value: ApiResponse<void>) => void;
+    let resolveApiCall!: (value: ApiResponse<void>) => void;
     const apiPromise = new Promise<ApiResponse<void>>((resolve) => {
       resolveApiCall = resolve;
     });
@@ -283,7 +283,7 @@ describe("createEvent saga - optimistic rendering", () => {
     expect(dayEventIdsDuringCall).toContain(optimisticId);
 
     // Resolve the API call
-    resolveApiCall?.({
+    resolveApiCall({
       status: 200,
     } as ApiResponse<void>);
 
@@ -552,7 +552,9 @@ describe("pending events state management", () => {
 
       iterator.next();
       expect(
-        iterator.next(stateAfterCreate.events.entities.value?.[eventId]).value,
+        iterator.next(
+          stateAfterCreate.events.entities.value?.[eventId] as never,
+        ).value,
       ).toEqual(put(pendingEventsSlice.actions.add(eventId)));
     });
 
@@ -587,7 +589,7 @@ describe("pending events state management", () => {
       } as never);
 
       iterator.next();
-      expect(iterator.next(existingEvent).value).toEqual(
+      expect(iterator.next(existingEvent as never).value).toEqual(
         put(pendingEventsSlice.actions.add(eventId)),
       );
       expect(iterator.next().value).toEqual(
@@ -636,7 +638,7 @@ describe("pending events state management", () => {
       } as never);
 
       iterator.next();
-      expect(iterator.next(existingEvent).value).toEqual(
+      expect(iterator.next(existingEvent as never).value).toEqual(
         put(pendingEventsSlice.actions.add(eventId)),
       );
       expect(iterator.next().value).toEqual(
diff --git a/packages/web/src/views/Calendar/components/Draft/hooks/actions/submit.parser.test.ts b/packages/web/src/views/Calendar/components/Draft/hooks/actions/submit.parser.test.ts
index d563fdf99..e608d09e8 100644
--- a/packages/web/src/views/Calendar/components/Draft/hooks/actions/submit.parser.test.ts
+++ b/packages/web/src/views/Calendar/components/Draft/hooks/actions/submit.parser.test.ts
@@ -5,23 +5,60 @@ import {
 } from "@web/common/types/web.event.types";
 import { afterAll, describe, expect, it, mock } from "bun:test";
 
+const createMockGridPosition = (): Schema_GridEvent["position"] => ({
+  isOverlapping: false,
+  totalEventsInGroup: 1,
+  widthMultiplier: 1,
+  horizontalOrder: 1,
+  dragOffset: { x: 0, y: 0 },
+  initialX: null,
+  initialY: null,
+});
+
+const createMockGridEvent = (
+  overrides: Partial<Schema_GridEvent> = {},
+): Schema_GridEvent => ({
+  _id: "test-grid-event-id",
+  title: "Test Grid Event",
+  startDate: "2024-01-15T10:00:00Z",
+  endDate: "2024-01-15T11:00:00Z",
+  isAllDay: false,
+  isSomeday: false,
+  origin: Origin.COMPASS,
+  priority: Priorities.UNASSIGNED,
+  user: "test-user",
+  position: createMockGridPosition(),
+  ...overrides,
+});
+
+const createMockSomedayEvent = (
+  overrides: Partial<Schema_SomedayEvent> = {},
+): Schema_SomedayEvent => ({
+  _id: "test-someday-event-id",
+  title: "Test Someday Event",
+  startDate: "2024-01-15T10:00:00Z",
+  endDate: "2024-01-15T11:00:00Z",
+  isAllDay: false,
+  isSomeday: true,
+  origin: Origin.COMPASS,
+  priority: Priorities.UNASSIGNED,
+  user: "test-user",
+  order: 1,
+  ...overrides,
+});
+
 const validateGridEvent = mock(
   (event: Schema_GridEvent): Schema_GridEvent => event,
 );
 const validateSomedayEvent = mock(
   (event: Schema_SomedayEvent): Schema_SomedayEvent => event,
 );
-const assembleGridEvent = mock((event: Partial<Schema_GridEvent>) => ({
-  ...event,
-  position: {
-    isOverlapping: false,
-    widthMultiplier: 1,
-    horizontalOrder: 1,
-    dragOffset: { y: 0 },
-    initialX: null,
-    initialY: null,
-  },
-}));
+const assembleGridEvent = mock((event: Partial<Schema_GridEvent>) =>
+  createMockGridEvent({
+    ...event,
+    position: event.position ?? createMockGridPosition(),
+  }),
+);
 
 mock.module("@web/common/validators/grid.event.validator", () => ({
   validateGridEvent,
@@ -39,45 +76,6 @@ const { OnSubmitParser, parseSomedayEventBeforeSubmit, prepEventBeforeSubmit } =
   require("./submit.parser") as typeof import("./submit.parser");
 
 describe("submit.parser", () => {
-  const createMockGridEvent = (
-    overrides: Partial<Schema_GridEvent> = {},
-  ): Schema_GridEvent => ({
-    _id: "test-grid-event-id",
-    title: "Test Grid Event",
-    startDate: "2024-01-15T10:00:00Z",
-    endDate: "2024-01-15T11:00:00Z",
-    isAllDay: false,
-    isSomeday: false,
-    origin: Origin.COMPASS,
-    priority: Priorities.UNASSIGNED,
-    user: "test-user",
-    position: {
-      isOverlapping: false,
-      widthMultiplier: 1,
-      horizontalOrder: 1,
-      dragOffset: { y: 0 },
-      initialX: null,
-      initialY: null,
-    },
-    ...overrides,
-  });
-
-  const createMockSomedayEvent = (
-    overrides: Partial<Schema_SomedayEvent> = {},
-  ): Schema_SomedayEvent => ({
-    _id: "test-someday-event-id",
-    title: "Test Someday Event",
-    startDate: "2024-01-15T10:00:00Z",
-    endDate: "2024-01-15T11:00:00Z",
-    isAllDay: false,
-    isSomeday: true,
-    origin: Origin.COMPASS,
-    priority: Priorities.UNASSIGNED,
-    user: "test-user",
-    order: 1,
-    ...overrides,
-  });
-
   describe("OnSubmitParser", () => {
     describe("constructor", () => {
       it("should initialize with a grid event", () => {
@@ -276,9 +274,10 @@ describe("submit.parser", () => {
       const draft = createMockGridEvent({
         position: {
           isOverlapping: true,
+          totalEventsInGroup: 2,
           widthMultiplier: 0.5,
           horizontalOrder: 2,
-          dragOffset: { y: 10 },
+          dragOffset: { x: 0, y: 10 },
           initialX: 100,
           initialY: 200,
         },
diff --git a/packages/web/src/views/Calendar/components/Draft/hooks/actions/useDraftActions.test.ts b/packages/web/src/views/Calendar/components/Draft/hooks/actions/useDraftActions.test.ts
index 68b00c724..d615485e2 100644
--- a/packages/web/src/views/Calendar/components/Draft/hooks/actions/useDraftActions.test.ts
+++ b/packages/web/src/views/Calendar/components/Draft/hooks/actions/useDraftActions.test.ts
@@ -50,9 +50,10 @@ const createDraft = (
   user: "user-1",
   position: {
     isOverlapping: false,
+    totalEventsInGroup: 1,
     widthMultiplier: 1,
     horizontalOrder: 1,
-    dragOffset: { y: 0 },
+    dragOffset: { x: 0, y: 0 },
     initialX: null,
     initialY: null,
   },
@@ -134,7 +135,7 @@ describe("useDraftActions", () => {
       reason: null,
       value: {
         count: 1,
-        data: [draft._id],
+        data: ["event-1"],
         offset: 0,
         page: 1,
         pageSize: 1,
diff --git a/packages/web/src/views/Calendar/components/Draft/hooks/effects/useDraftEffects.test.ts b/packages/web/src/views/Calendar/components/Draft/hooks/effects/useDraftEffects.test.ts
index 7c6f88a40..0774ab217 100644
--- a/packages/web/src/views/Calendar/components/Draft/hooks/effects/useDraftEffects.test.ts
+++ b/packages/web/src/views/Calendar/components/Draft/hooks/effects/useDraftEffects.test.ts
@@ -24,9 +24,10 @@ const createDraft = (
   user: "user-1",
   position: {
     isOverlapping: false,
+    totalEventsInGroup: 1,
     widthMultiplier: 1,
     horizontalOrder: 1,
-    dragOffset: { y: 0 },
+    dragOffset: { x: 0, y: 0 },
     initialX: null,
     initialY: null,
   },
diff --git a/packages/web/src/views/Calendar/components/Event/Grid/GridEventPreview/snap.grid.test.ts b/packages/web/src/views/Calendar/components/Event/Grid/GridEventPreview/snap.grid.test.ts
index 80ece4c4d..35f48df17 100644
--- a/packages/web/src/views/Calendar/components/Event/Grid/GridEventPreview/snap.grid.test.ts
+++ b/packages/web/src/views/Calendar/components/Event/Grid/GridEventPreview/snap.grid.test.ts
@@ -15,9 +15,6 @@ describe("snapToGrid", () => {
       y: 0,
       bottom: 0,
       right: 0,
-      toJSON: () => {
-        throw new Error("Function not implemented.");
-      },
     },
     hourHeight: 60,
     colWidths: Array(7).fill(100) as number[],
diff --git a/packages/web/src/views/Day/components/Toasts/UndoToast/UndoDeleteToast.test.tsx b/packages/web/src/views/Day/components/Toasts/UndoToast/UndoDeleteToast.test.tsx
index 480e57546..0e120153f 100644
--- a/packages/web/src/views/Day/components/Toasts/UndoToast/UndoDeleteToast.test.tsx
+++ b/packages/web/src/views/Day/components/Toasts/UndoToast/UndoDeleteToast.test.tsx
@@ -3,7 +3,12 @@ import "@testing-library/jest-dom";
 import { fireEvent, render, screen } from "@testing-library/react";
 import { getModifierKeyTestId } from "@web/common/utils/shortcut/shortcut.util";
 
-const toastMock = mock(() => "test-toast-id");
+type ToastMock = ReturnType<typeof mock> & {
+  dismiss: ReturnType<typeof mock>;
+  update: ReturnType<typeof mock>;
+};
+
+const toastMock = mock(() => "test-toast-id") as ToastMock;
 toastMock.dismiss = mock();
 toastMock.update = mock();
 
@@ -50,7 +55,10 @@ describe("UndoDeleteToast", () => {
       );
 
       const toastButton = screen.getByText("Deleted").closest("button");
-      fireEvent.click(toastButton!);
+      if (!toastButton) {
+        throw new Error("Expected toast button");
+      }
+      fireEvent.click(toastButton);
 
       expect(mockOnRestore).toHaveBeenCalledTimes(1);
     });
@@ -63,7 +71,10 @@ describe("UndoDeleteToast", () => {
       );
 
       const toastButton = screen.getByText("Deleted").closest("button");
-      fireEvent.click(toastButton!);
+      if (!toastButton) {
+        throw new Error("Expected toast button");
+      }
+      fireEvent.click(toastButton);
 
       expect(toastMock.dismiss).toHaveBeenCalledWith(testToastId);
     });
diff --git a/packages/web/src/views/Day/context/__tests__/DNDTasksContext.test.tsx b/packages/web/src/views/Day/context/__tests__/DNDTasksContext.test.tsx
index 82b6f9ccc..ebc0cf9f6 100644
--- a/packages/web/src/views/Day/context/__tests__/DNDTasksContext.test.tsx
+++ b/packages/web/src/views/Day/context/__tests__/DNDTasksContext.test.tsx
@@ -116,9 +116,12 @@ describe("DNDTasksProvider", () => {
     expect(screen.getByTestId("context-value")).toHaveTextContent(
       "has-context",
     );
-    expect(contextValue).toBeDefined();
-    expect(typeof contextValue.onDragStart).toBe("function");
-    expect(typeof contextValue.onDragEnd).toBe("function");
+    const value = contextValue as DNDTasksContextValue | null;
+    if (!value) {
+      throw new Error("Expected DND tasks context to be available");
+    }
+    expect(typeof value.onDragStart).toBe("function");
+    expect(typeof value.onDragEnd).toBe("function");
   });
 
   it("should call setSelectedTaskIndex and announce on drag start", () => {
diff --git a/packages/web/src/views/Day/hooks/events/useAgendaInteractionsAtCursor.test.ts b/packages/web/src/views/Day/hooks/events/useAgendaInteractionsAtCursor.test.ts
index 5e9b1c437..faee240c4 100644
--- a/packages/web/src/views/Day/hooks/events/useAgendaInteractionsAtCursor.test.ts
+++ b/packages/web/src/views/Day/hooks/events/useAgendaInteractionsAtCursor.test.ts
@@ -1,4 +1,7 @@
-import { type useFloating } from "@floating-ui/react";
+import {
+  type useFloating,
+  type useInteractions as useFloatingInteractions,
+} from "@floating-ui/react";
 import { renderHook } from "@testing-library/react";
 import { afterAll, beforeEach, describe, expect, it, mock } from "bun:test";
 
@@ -40,7 +43,11 @@ describe("useAgendaInteractionsAtCursor", () => {
     const mockHover = {};
     const mockFocus = {};
     const mockDismiss = {};
-    const mockInteractions = { getReferenceProps: mock() };
+    const mockInteractions = {
+      getFloatingProps: mock(),
+      getItemProps: mock(),
+      getReferenceProps: mock(),
+    } as ReturnType<typeof useFloatingInteractions>;
 
     useClick.mockReturnValue(mockClick);
     useHover.mockReturnValue(mockHover);
diff --git a/packages/web/src/views/Day/util/time/time.util.test.ts b/packages/web/src/views/Day/util/time/time.util.test.ts
index d98f36d28..43bb84108 100644
--- a/packages/web/src/views/Day/util/time/time.util.test.ts
+++ b/packages/web/src/views/Day/util/time/time.util.test.ts
@@ -34,7 +34,7 @@ describe("setupMinuteSync", () => {
         intervalCallback = () => callback();
       }
       return intervalId;
-    }) as typeof setInterval);
+    }) as unknown as typeof setInterval);
     setTimeoutSpy = spyOn(globalThis, "setTimeout").mockImplementation(((
       callback: TimerHandler,
     ) => {
@@ -42,7 +42,7 @@ describe("setupMinuteSync", () => {
         timeoutCallback = () => callback();
       }
       return timeoutId;
-    }) as typeof setTimeout);
+    }) as unknown as typeof setTimeout);
   });
 
   afterEach(() => {
diff --git a/packages/web/src/views/Forms/EventForm/DateControlsSection/RecurrenceSection/RecurrenceSection.test.tsx b/packages/web/src/views/Forms/EventForm/DateControlsSection/RecurrenceSection/RecurrenceSection.test.tsx
index 88e6f5db3..7447286e2 100644
--- a/packages/web/src/views/Forms/EventForm/DateControlsSection/RecurrenceSection/RecurrenceSection.test.tsx
+++ b/packages/web/src/views/Forms/EventForm/DateControlsSection/RecurrenceSection/RecurrenceSection.test.tsx
@@ -3,6 +3,7 @@ import userEvent from "@testing-library/user-event";
 import { useCallback, useState } from "react";
 import { ThemeProvider } from "styled-components";
 import { Origin, Priorities } from "@core/constants/core.constants";
+import { type Schema_Event } from "@core/types/event.types";
 import { SessionContext } from "@web/auth/compass/session/SessionProvider";
 import {
   markBackendUnavailable,
@@ -36,7 +37,7 @@ function renderRecurrenceSection({
   const setEventSpy = mock();
 
   function Harness() {
-    const [event, setEvent] = useState<Schema_GridEvent | null>(baseEvent());
+    const [event, setEvent] = useState<Schema_Event | null>(baseEvent());
     const handleSetEvent = useCallback<typeof setEvent>((nextEvent) => {
       setEventSpy(nextEvent);
       setEvent(nextEvent);
diff --git a/packages/web/tsconfig.test.json b/packages/web/tsconfig.test.json
new file mode 100644
index 000000000..81fdd9bd8
--- /dev/null
+++ b/packages/web/tsconfig.test.json
@@ -0,0 +1,28 @@
+{
+  "extends": "./tsconfig.json",
+  "include": [
+    "./declaration.d.ts",
+    "./src/**/*.d.ts",
+    "./src/**/*.test.ts",
+    "./src/**/*.test.tsx",
+    "./src/**/*.test.utils.ts",
+    "./src/**/*.test.utils.tsx",
+    "./src/**/*.spec.ts",
+    "./src/**/*.spec.tsx",
+    "./src/**/*.test-util.ts",
+    "./src/**/*.test-util.tsx"
+  ],
+  "compilerOptions": {
+    "noEmit": true,
+    "target": "ES2022",
+    "module": "ES2022",
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "skipLibCheck": true,
+    "allowSyntheticDefaultImports": true,
+    "paths": {
+      "@web/*": ["./src/*"],
+      "@core/*": ["../core/src/*"],
+      "@backend/*": ["../backend/src/*"]
+    }
+  }
+}