Which piece owns
which job?

This reference introduces vocabulary; it does not mark these concepts as mastered. Each definition points back to the lesson that explains it.

Choose by responsibility

Trace a failure to the right boundary

• The page loads but data is fake: inspect the tRPC procedure and shared query; the starter begins with placeholders.
• A binding exists in TypeScript but fails at runtime: inspect the selected environment, actual binding configuration, and entrypoint initialization.
• A changed link redirects to an old URL: inspect cached configuration and invalidation, then the authoritative database record.
• The redirect works but analytics are missing: inspect the producer send, consumer validation, errors, retries, and dead-letter path.
• The AI reports unknown availability: inspect the saved page text and screenshot before rewriting the prompt.
• A workflow fails after screenshot support: inspect non-stream step-result size and apply lesson 34’s R2-first artifact handling.
• A new live-map tab is empty: distinguish the tutorial’s initial-history gap from failure to receive new events.
• Checkout succeeds but the plan does not update: inspect the matching Stripe mode, webhook delivery, signing secret, and subscription record.
• A paid feature is available to everyone: inspect server entitlement checks; billing alone does not enforce a quota.

Added diagnostic prompts based on the course demonstrations; use the relevant lesson to verify the actual failure in your implementation.

Vocabulary

Worker

Server-side code invoked by requests or other events; the hosting unit for the course’s two services. Lesson 04

Entrypoint

The exported handler or class through which the runtime invokes an application, workflow, or object. Lesson 05

Binding

A configured connection exposed to Worker code for accessing a resource or another service. Lesson 06

Monorepo

One repository containing multiple applications and shared packages; shared source does not imply one deployment. Lesson 02

TanStack Router

The UI’s navigation and route-loading layer. Lesson 07

TanStack Query

Client-side management of server data, including cached queries and invalidation after mutations. Lesson 07

tRPC

Typed communication between the TypeScript frontend and server procedures. Lesson 07

Zod

Runtime schema validation used to check actual values at API, queue, and AI-output boundaries. Lesson 23

D1

The SQL database for links, click records, evaluations, and authentication/subscription tables. Lesson 08

Drizzle

The typed SQL/data-access layer used to query D1 from shared Data Ops code. Lesson 09

KV

A key-value store used here as a read cache for link configuration; it is eventually consistent. Lesson 17

R2

Object storage used here for rendered HTML, extracted text, and screenshots. Lesson 31

Queue

A durable handoff between a producer and consumer once a message has been accepted. Lesson 19

Dead-letter queue

A recovery destination for messages that exhaust the configured delivery retries. Lesson 24

Idempotency

Designing an operation so repeating the same logical event does not add an unintended extra effect. Lesson 24

Workflow

An execution composed of named steps with persisted progress and retry behavior. Lesson 25

Browser Rendering

The course’s name for the remote browser service used to load pages and collect evidence. Lesson 27

Workers AI

The model service used to classify extracted destination-page content. Lesson 28

Durable Object

An addressable stateful coordinator; the same object identity selects the same logical state. Lesson 35

Alarm

A persisted future invocation associated with a Durable Object. Repeating work needs an explicit scheduling policy. Lesson 38

WebSocket

A persistent two-way connection used here to push click updates to dashboard viewers. Lesson 41

Service binding

An internal connection between Workers; it is distinct from a browser’s public URL. Lesson 44

Authentication

Establishing the identity represented by a request/session. Lesson 49

Authorization

Deciding whether that identity may access a record or perform an operation. Lesson 52

Webhook

An HTTP event notification sent by a service such as Stripe to the application. Lesson 56

Entitlement

The feature or quota a plan grants; the server must enforce it separately from taking payment. Lesson 59

Migration

A controlled change to a database schema or runtime resource definition; the two uses must be distinguished. Lesson 45

CPU time / wall time

Active computation versus total elapsed duration, which can include waiting for I/O. Lesson 04

Six quick checks

Choose from memory, then explain why the other two choices do not fit.

Build in layers

Suggested practice sequence: first make one link persist and redirect correctly. Then add one observable queued event. Next add an evaluation whose saved evidence you can inspect. Add coordinated scheduling and live updates only after those paths make sense. Finish with explicit identity, billing synchronization, entitlement rules, and tests for the failures you can name. This is added study guidance, not a claim that all those final checks are completed by the recording.