A rejected form still looks fine on screen

Validation code is written once, glanced at in the browser with one obviously-bad value, and never driven again. The bug that ships is never the value you tried. It's the one you didn't: a submit button that isn't disabled until the field blurs, a button that's disabled only by CSS and still clickable, or a handler that fires the request before the check finishes.

Reticle can drive the real form and check all three failure points at once. Not set up? Follow the reticle skill: it installs Reticle, asks the user before init changes the app's files, and proves one flow.

Read this before you start: the browser's own validation can mask the app's

required, pattern, type="email" and friends stop the browser at the constraint-validation bubble before your app's JS ever runs. If you assert on that native tooltip, you've verified the browser, not the code you're supposed to be testing. Confirm the error you're checking is the app's own element (a testid, a role, a rendered string), not a :invalid pseudo-state, before you trust the verdict. If the form relies on native validation alone with no app-level check behind it, that's the finding: say so, don't paper over it with a predicate that happens to pass.

Trigger the rejection

Name the consequence before you act, same as any Reticle drive:

reticle_look({ action: "page", sessionId, mode: "interactive" })   // get refs for the field and submit control

reticle_act_and_wait({ sessionId, ref, action: "fill", args: { value: "<invalid>" }, until: { kind: "allOf", predicates: [
  { kind: "element", query: { testid: "field-error" } },
  { kind: "element", query: { role: "button", name: "Submit" }, state: "disabled" },
]}})