diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
new file mode 100644
index 0000000..0aff1b2
--- /dev/null
+++ b/.github/copilot-instructions.md
@@ -0,0 +1,61 @@
+## Copilot / AI Agent Instructions for this repository
+
+Purpose: quick, practical guidance so an AI coding agent can be productive immediately.
+
+- **Big picture**: This is a single-page Next.js (App Router) app that tracks bicycle wear parts. The UI lives under `app/` (React Server/Client components) and server logic is implemented as Next API Route handlers under `app/api/*` (files named `route.ts`). Database access is via Prisma + SQLite; the Prisma client is in `lib/prisma.ts` and schema in `prisma/schema.prisma`.
+
+- **Key directories / files**:
+  - `app/` — Next App Router. Routes and React components live here.
+    - `app/api/` — Route handlers (e.g. `app/api/bikes/route.ts`, `app/api/bikes/[id]/route.ts`). These are the server-side endpoints used by the frontend.
+    - `app/components/` — small client components. Note many components include `'use client'` at the top (e.g. `BikeDetail.tsx`).
+  - `lib/prisma.ts` — exports Prisma client; import this in route handlers.
+  - `lib/validations.ts` — Zod schemas used both server-side and in tests.
+  - `prisma/schema.prisma` — database schema (SQLite). Use Prisma commands after edits.
+  - `types/` — TypeScript types used across UI and APIs (e.g. `BikeWithParts`).
+  - `__tests__/` — Vitest tests; split into `api/` and `lib/` tests.
+
+- **Runtime & stack**:
+  - Uses Bun as the development runtime (`bun run dev` in README) but apps run as Next.js (v14). Keep using `bun` commands as the project expects.
+  - Tailwind CSS for styling, Zod for validation, Prisma for DB.
+
+- **Project-specific conventions and patterns**:
+  - Next App Router pattern: server code under `app/api/*` uses `route.ts` exports. Edit these when changing backend behavior.
+  - Client components explicitly use `'use client'`. If a component needs browser APIs or state/hooks, it must be a client component.
+  - The repo uses an import alias `@` mapped to the project root (see `vitest.config.ts`). Tests and code reference `@/` paths — preserve that style.
+  - Database changes: update `prisma/schema.prisma`, then run Prisma generate/push. The README suggests `bunx prisma generate` and `bunx prisma db push`.
+
+- **Developer workflows (commands)** — copyable examples:
+  - Install deps: `bun install`
+  - Dev server: `bun run dev` (runs `next dev`)
+  - Build: `bun run build`
+  - Prisma: `bunx prisma generate` then `bunx prisma db push` (or `bun run db:push` from package.json)
+  - Open DB UI: `bun run db:studio`
+
+- **Testing**:
+  - Tests run with Vitest. Root scripts in `package.json`:
+    - `bun run test` — runs `vitest run --exclude '**/validations.test.ts' && bun test __tests__/lib/validations.test.ts` (note: validations tests are run separately in this project).
+    - `bun run test:all` — runs `vitest run`.
+    - `bun run test:ui` — runs `vitest --ui`.
+  - `vitest.config.ts` sets `environment: 'node'`, `globals: true`, and the alias `@` to the project root — tests assume these settings.
+  - To run a single test file use: `vitest run __tests__/api/bikes.test.ts` or run the npm script with `bun run`.
+
+- **Editing APIs & DB changes**:
+  - When changing a route under `app/api/*`, update or add corresponding tests in `__tests__/api/*`.
+  - When changing `prisma/schema.prisma`, run `bunx prisma generate` and `bunx prisma db push`. Update any affected `lib/prisma.ts` usages if the client API changes.
+
+- **What to avoid / gotchas**:
+  - Do not assume a separate backend service — API routes are in-repo Next route handlers.
+  - Pay attention to client vs server components (`'use client'`). Moving code between them requires changing data fetching approaches.
+  - Tests rely on the `@` alias — preserve import paths like `@/lib/validations` rather than relative deep paths when modifying code.
+
+- **Where to look for examples**:
+  - API patterns: `app/api/bikes/route.ts` and `app/api/bikes/[id]/route.ts`.
+  - Prisma usage: `lib/prisma.ts` and `prisma/schema.prisma`.
+  - Validations: `lib/validations.ts` and `__tests__/lib/validations.test.ts`.
+  - Client component example: `app/components/BikeDetail.tsx` uses local state, child forms (`WearPartForm`) and lists (`WearPartList`).
+
+- **If something is unclear**: ask the maintainer these quick questions before making changes:
+  1. Do you want to keep using `bun` for tests and dev, or prefer `npm`/`pnpm` wrappers? (README uses `bun`.)
+ 2. Are there deployment targets or environment variables not in the repo? (DB URL / secrets)
+
+Be concise in edits: when changing API behavior, update `app/api/*` and the corresponding tests in `__tests__/api/` in the same PR.
diff --git a/__tests__/lib/validations.test.ts b/__tests__/lib/validations.test.ts
index 2015807..f6909ba 100644
--- a/__tests__/lib/validations.test.ts
+++ b/__tests__/lib/validations.test.ts
@@ -235,7 +235,8 @@ describe('Validation Schemas', () => {
           expect(result.data.purchaseDate).toBeInstanceOf(Date)
         } else {
           // If it's still a string, it should be parseable
-          expect(new Date(result.data.purchaseDate as string)).toBeInstanceOf(Date)
+          const parsed = new Date(String(result.data.purchaseDate))
+          expect(parsed).toBeInstanceOf(Date)
         }
       }
     })
diff --git a/app/bikes/[id]/page.tsx b/app/bikes/[id]/page.tsx
index 8701cc6..e71928b 100644
--- a/app/bikes/[id]/page.tsx
+++ b/app/bikes/[id]/page.tsx
@@ -45,6 +45,6 @@ export default function BikeDetailPage() {
     return null
   }
 
-  return <BikeDetail bike={bike} onUpdate={fetchBike} />
+  return <BikeDetail bike={bike} onUpdate={() => fetchBike(params.id as string)} />
 }
 
diff --git a/app/components/BikeDetail.tsx b/app/components/BikeDetail.tsx
index 66070d3..1b68aaf 100644
--- a/app/components/BikeDetail.tsx
+++ b/app/components/BikeDetail.tsx
@@ -91,7 +91,12 @@ export default function BikeDetail({ bike, onUpdate }: BikeDetailProps) {
 
         <WearPartList
           bikeId={bike.id}
-          parts={bike.wearParts}
+          parts={bike.wearParts.map((p) => ({
+            // ensure each part has a `maintenanceHistory` array to satisfy WearPartList prop types
+            ...p,
+            // some server queries may not include maintenanceHistory; default to empty array
+            maintenanceHistory: (p as any).maintenanceHistory ?? [],
+          }))}
           bikeCurrentMileage={bike.currentMileage}
           onUpdate={onUpdate}
         />
diff --git a/package.json b/package.json
index 12bd95b..9411f09 100644
--- a/package.json
+++ b/package.json
@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "private": true,
   "scripts": {
-    "dev": "next dev",
+    "dev": "next dev --port 3001",
     "build": "next build",
     "start": "next start",
     "lint": "next lint",
diff --git a/types/index.ts b/types/index.ts
index 7915ee6..fcc1d01 100644
--- a/types/index.ts
+++ b/types/index.ts
@@ -1,14 +1,14 @@
 import { Bike, WearPart, MaintenanceHistory } from '@prisma/client'
 
-export type BikeWithParts = Bike & {
-  wearParts: WearPart[]
-}
-
 export type WearPartWithHistory = WearPart & {
   maintenanceHistory: MaintenanceHistory[]
   bike: Bike
 }
 
+export type BikeWithParts = Bike & {
+  wearParts: WearPartWithHistory[]
+}
+
 export type MaintenanceHistoryWithPart = MaintenanceHistory & {
   wearPart: WearPart
 }