backend/tsconfig.json had no incremental setting, so every tsc run
re-checked the full project from cold. The two frontend tsconfigs
already declared a tsBuildInfoFile path under node_modules/.tmp/ but
without incremental: true the file was never written, and the path
itself sits inside node_modules where npm ci wipes it on every fresh
install — neither of which actually persists incremental state.
Add incremental: true to all three configs and drop the broken
tsBuildInfoFile overrides. TypeScript's default places the buildinfo
next to the tsconfig (e.g. backend/tsconfig.tsbuildinfo); the root
.gitignore already covers *.tsbuildinfo so nothing leaks into git.
Local cold-vs-warm tsc --noEmit on the backend dropped from ~3.0s
to ~1.4s — ~2x speedup on the warm path. CI builds are still cold
because runners do not cache the buildinfo between jobs; that is a
separate workflow change.
Anso