Problem

On a clean checkout, npm test in frontend/ai.client can fail in src/app/app.spec.ts with:

The injectable 'PlatformLocation' needs to be compiled using the JIT compiler, but '@angular/compiler' is not available

raised from import('./app') → @angular/router → @angular/common _platform_location-chunk. Both tests in the file fail (module-level import failure). The failure is flaky and environment/timing dependent.

Root cause

• @angular/build:unit-test builds specs with externalPackages: true, so @angular/* packages are never bundled/linked — vitest loads the raw npm fesm2022 files at runtime (_platform_location-chunk.mjs is a file shipped inside @angular/common 21.2).
• Those shipped chunks contain partial declarations (ɵɵngDeclareInjectable/ɵɵngDeclareFactory) that compile eagerly at module evaluation via getCompilerFacade — they require @angular/compiler the moment the module is evaluated, not at first injection.
• The compiler was only present incidentally: the builder's init-testbed setup imports @angular/core/testing, which transitively evaluates @angular/compiler. Nothing guarantees that ordering. app.spec.ts is uniquely exposed because it has no static Angular imports — when the evaluation order breaks, the whole file dies at import time.

Upstream reports of the same failure mode: angular/angular-cli#31993, angular/angular-cli#32095; the upstream remedy (angular/angular-cli#32304) is the same one applied here — guarantee the compiler is loaded.

Fix

• src/test-setup.ts — import '@angular/compiler';, wired via the test target's setupFiles in angular.json, so the JIT fallback is an explicit invariant in every vitest worker instead of an accident of import order.
• tsconfig.spec.json — includes the setup file in the spec TS program (the builder hard-errors otherwise).
• src/test-setup.spec.ts — guard spec mirroring app.spec.ts's shape (no static Angular imports): asserts the compiler facade is registered and that an unlinked partial-declared injectable actually JIT-compiles. If the setup file is ever removed, this fails deterministically instead of the suite failing flakily.
• shared-view.page.spec.ts — separate flake caught while soak-testing (1-in-9 full-suite runs): the file's first test pays the one-time dynamic page-chunk import and exceeded vitest's 5s default under parallel load (5011ms observed). Bumped that single test to 15s.

Verification

• 5 consecutive full ng test runs green (126 files / 1449 tests) on the pinned dependency tree (npm ci), including cold-cache runs (.angular/cache + node_modules/.vite removed).
• Confirmed setup-test-setup.js appears as a build entry point and runs before specs.
• Failure mode reproduced directly during diagnosis: a probe spec declaring an unlinked partial injectable fails/passes exactly according to compiler availability.

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