## Summary
https://github.com/user-attachments/assets/1e75cc9d-d9d2-4ef2-99f9-34450f5d8de7
Add background incremental type checking (`tsc --watch`) to the SDK dev
mode, so type regressions are caught when the generated API client
changes — without requiring a full rebuild of source files.
Previously, removing a field from the data model would regenerate the
API client, but existing front components/logic functions referencing
the removed field wouldn't surface type errors (since their source
didn't change, esbuild wouldn't rebuild them).
## What changed
- **Background `tsc --watch`**: a long-lived TypeScript watcher runs
alongside esbuild watchers, incrementally re-checking all files when the
generated client changes. Only logs on state transitions (errors appear
/ errors clear) to stay quiet.
- **Atomic client generation**: API client is now generated into a temp
directory and swapped in atomically, avoiding a race condition where
`tsc --watch` could see an empty `generated/` directory
mid-regeneration.
- **Step decoupling**: orchestrator steps no longer receive
`uploadFilesStep` directly. Instead, they use callbacks (`onFileBuilt`,
`onApiClientGenerated`), and each step manages its own `builtFileInfos`
state.
- **`apiClientChecksum` omitted from `ApplicationConfig`**: it's a
build-time computed value, same as `packageJsonChecksum`.
<img width="327" height="177" alt="image"
src="https://github.com/user-attachments/assets/02bd25bb-fa41-42b0-8d96-01c51bd4580c"
/>
<img width="529" height="452" alt="image"
src="https://github.com/user-attachments/assets/61f6e968-365b-4a5b-8f2b-a8419d6b1bd3"
/>
