diff --git a/.github/workflows/typecheck.yml b/.github/workflows/typecheck.yml
new file mode 100644
index 00000000..ea9f5e38
--- /dev/null
+++ b/.github/workflows/typecheck.yml
@@ -0,0 +1,34 @@
+# ================================================================
+# Prismatica (opposite-osiris) — astro check on every pull request
+# ================================================================
+# The web image runs `astro build`, which strips types and never typechecks, so a
+# missing import ships as a runtime ReferenceError (5333085: themeIcon). The check
+# lives here, not in the Dockerfile: a type-only error blocks the merge, never a build.
+# Runs in the Dockerfile's own base image so Node and pnpm match it exactly.
+# ================================================================
+
+name: Typecheck
+
+on:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  astro-check:
+    name: 🔎 astro check
+    runs-on: ubuntu-latest
+    container: node:22-alpine
+    env:
+      TRACK_BINOCLE_IN_DOCKER: "1"
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install
+        run: |
+          corepack enable && corepack prepare pnpm@11.5.1 --activate
+          pnpm install --frozen-lockfile --ignore-scripts --config.node-linker=hoisted
+
+      - name: astro check
+        run: node_modules/.bin/astro check
diff --git a/src/lib/email-validation.ts b/src/lib/email-validation.ts
index afcbf562..5592cf25 100644
--- a/src/lib/email-validation.ts
+++ b/src/lib/email-validation.ts
@@ -1,8 +1,10 @@
 import { validateEmail } from '../hooks/useAuth';
 
+export type FieldValidationState = 'idle' | 'warning' | 'error' | 'success';
+
 export type EmailValidationResult = {
 	valid: boolean;
-	state: 'idle' | 'warning' | 'error' | 'success';
+	state: FieldValidationState;
 	message: string;
 };
 
diff --git a/src/scripts/main.ts b/src/scripts/main.ts
index 630f425c..70887d54 100644
--- a/src/scripts/main.ts
+++ b/src/scripts/main.ts
@@ -1284,7 +1284,7 @@ function messageMentions(message: string, ...needles: string[]): boolean {
 
 
 
-import { validateEmailFormat, type EmailValidationResult } from '../lib/email-validation';
+import { validateEmailFormat, type EmailValidationResult, type FieldValidationState } from '../lib/email-validation';
 
 function emailValidationResult(field: HTMLInputElement): EmailValidationResult {
 	return validateEmailFormat(field.value.trim(), field.required, field.validity.valid);