A one-developer UI library rebuilt the template type-checking Angular ships by default

The habits show up in specific places. An agent trained on millions of Vue components and Angular modules reaches for a reactive store, and it adds its own submit listener beside the one the library already owns ^[4]. The core skill file that ships with @relax.js/core opens with the failure mode in one sentence: "Patterns carried over from React compile, type-check and do nothing" ^[5]. jgauffin has not used the framework whose idioms keep appearing. "I have not written React myself, but I have watched agents write it unprompted, and it is what they reach for when nobody tells them otherwise," he wrote ^[6].

What makes that class of error expensive is the size of the agent's feedback loop. It cannot open a browser. It reads files, greps for names, runs the type checker and runs the tests, so anything observable only at runtime is invisible to it ^[9]. A template expression that fails to resolve prints an empty string: a blank spot on the page for a human, a passing test for the agent ^[13].

jgauffin lists the four bugs that cost him the most time in Vue and Angular: a watch that fired a tick later than he thought, a computed that never recalculated because its dependency was read behind a condition, change detection that did not run because the update came from outside the zone, and an ngOnInit that assumed an @Input arriving on the next cycle ^[10]. None of them are visible in the file where the symptom appears, and the cause sits in the framework's scheduler, found with a breakpoint in DevTools ^[11]. An agent instead concludes the file it opened is correct and starts changing things speculatively. "That is the most expensive thing an agent does: producing plausible edits in the wrong place," he wrote ^[12]. His alternative is code where the update is this.nameSpan.textContent = user.name at the place where user changed; a reviewer or an agent can verify that by reading ^[22].

He also throws out the usual argument for a small library on its own terms. Fitting in the context window is true and beside the point, he writes, because an agent needs correct memory of the framework's behaviour, and that memory rots with every major version ^[18]. What he wants is greppability: r-click="save()" in a template is one grep from save, and a connection that is not a shared literal name is one the agent will guess at ^[17].

The price of the string template is visible in what had to be built. Angular's compiler and vue-tsc make a template typo a build error before anything runs ^[7]; in a library where the template is a string, {{user.naem}} stays a string until the page renders ^[8]. Two pieces now cover that. Quiet failures report through a single error channel, and a test helper turns the channel into assertions ^[14]. npx @relax.js/core check resolves every template expression against the TypeScript types at the call site and prints tsc-style lines ^[15]. The second one reproduces, for string templates, the check the Angular and Vue toolchains already run in the build ^[20].

Two conditions have to hold for this to transfer. Your templates need call sites typed well enough that a checker can resolve expressions against them ^[15], and the bugs eating your review time need to be the scheduler-timing kind, since those are the ones an explicit update removes ^[10][22]. The post does not report error counts or a measured comparison between the two setups, so this is one developer's account of his own projects ^[21].