Stabilize e2e against Vite dev hydration race

Two issues caused the same class of flake locally:

1. Default workers were CPU-count, but the journal/planner are served
   by Vite dev (not the production build CI uses). Cold-compiling
   `/api/auth/register` under N parallel hits produced 30s timeouts
   on a quarter of runs. Set workers to 1 in both environments for
   parity with CI.
2. Even sequentially, a button is clickable per Playwright's
   actionability check before React has hydrated its `onClick`. So
   the first click after a navigation could fire native form submit
   (or do nothing), which manifested as "URL never changed to /" or
   "menuitem Log Out never appeared". Add a `waitForHydration` helper
   that polls for React fibers (`__reactProps$<id>`) attached to a
   DOM node and call it after each cross-page navigation that ends
   in an interactive form or dropdown.

CI is unaffected (production builds hydrate fast and didn't expose
either bug), but the helper is harmless there.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

e2e/auth.test.ts

@@ -1,4 +1,4 @@
-import { test, expect, type CDPSession, type Page } from "./fixtures/test";
+import { test, expect, waitForHydration, type CDPSession, type Page } from "./fixtures/test";
 
 // Virtual authenticator helpers
 async function setupVirtualAuthenticator(cdp: CDPSession) {
@@ -23,6 +23,7 @@ async function removeVirtualAuthenticator(cdp: CDPSession, authenticatorId: stri
 async function registerUser(page: Page, email: string, username: string) {
   await page.goto("/auth/register");
   await expect(page.getByRole("heading", { name: "Register" })).toBeVisible();
+  await waitForHydration(page);
   await page.getByLabel("Email").click();
   await page.getByLabel("Email").fill(email);
   await page.getByLabel("Username").click();
@@ -39,6 +40,7 @@ async function logout(page: Page, accountLabel: string) {
   // The account cluster lives inside an avatar dropdown now. Click the
   // avatar (its aria-label is displayName || username), then click the
   // Log Out menuitem inside the popup.
+  await waitForHydration(page);
   await page.getByRole("navigation").getByRole("button", { name: accountLabel }).click();
   await page.getByRole("menuitem", { name: "Log Out" }).click();
   await expect(page.getByRole("navigation").getByRole("link", { name: "Sign In" })).toBeVisible({ timeout: 5000 });

e2e/explore.test.ts

@@ -1,4 +1,4 @@
-import { test, expect, type CDPSession, type Page } from "./fixtures/test";
+import { test, expect, waitForHydration, type CDPSession, type Page } from "./fixtures/test";
 
 async function setupVirtualAuthenticator(cdp: CDPSession) {
   await cdp.send("WebAuthn.enable");
@@ -17,6 +17,7 @@ async function setupVirtualAuthenticator(cdp: CDPSession) {
 async function registerUser(page: Page, email: string, username: string) {
   await page.goto("/auth/register");
   await expect(page.getByRole("heading", { name: "Register" })).toBeVisible();
+  await waitForHydration(page);
   await page.getByLabel("Email").fill(email);
   await page.getByLabel("Username").fill(username);
   await page.getByRole("checkbox").check();

e2e/fixtures/test.ts

@@ -74,5 +74,29 @@ export const test = base.extend({
   },
 });
 
+/**
+ * Wait until React has hydrated the current page. Vite dev injects scripts
+ * asynchronously, so a button/form is visible (and clickable per Playwright's
+ * actionability check) before its React `onClick`/`onSubmit` is wired up.
+ * Without this, the first click after navigation is a coin flip on a cold
+ * dev server — controlled inputs ignore the keystrokes and submit handlers
+ * never run, so the form posts empty fields or natively GETs to itself.
+ *
+ * Detects hydration by checking for React's `__reactProps$<id>` property
+ * which is attached during commit. CI uses production builds where this
+ * isn't a problem, but the check is cheap and harmless there.
+ */
+export async function waitForHydration(page: import("@playwright/test").Page) {
+  await page.waitForFunction(
+    () => {
+      const el = document.body.querySelector("button, input, form, a");
+      if (!el) return false;
+      return Object.keys(el).some((k) => k.startsWith("__reactProps$"));
+    },
+    null,
+    { timeout: 10000 },
+  );
+}
+
 export { expect };
 export type { CDPSession, Page } from "@playwright/test";

e2e/notifications.test.ts

@@ -1,4 +1,4 @@
-import { test, expect, type CDPSession, type Page } from "./fixtures/test";
+import { test, expect, waitForHydration, type CDPSession, type Page } from "./fixtures/test";
 
 async function setupVirtualAuthenticator(cdp: CDPSession) {
   await cdp.send("WebAuthn.enable");
@@ -17,6 +17,7 @@ async function setupVirtualAuthenticator(cdp: CDPSession) {
 async function registerUser(page: Page, email: string, username: string) {
   await page.goto("/auth/register");
   await expect(page.getByRole("heading", { name: "Register" })).toBeVisible();
+  await waitForHydration(page);
   await page.getByLabel("Email").fill(email);
   await page.getByLabel("Username").fill(username);
   await page.getByRole("checkbox").check();
@@ -63,6 +64,7 @@ test.describe("Notifications", () => {
 
     // A follows B (auto-accept).
     await page.goto(`/users/${bUsername}`);
+    await waitForHydration(page);
     await page.getByRole("button", { name: "Follow" }).click();
     await expect(page.getByRole("button", { name: "Unfollow" })).toBeVisible({ timeout: 5000 });
 

e2e/public-content.test.ts

@@ -1,4 +1,4 @@
-import { test, expect, type CDPSession, type Page } from "./fixtures/test";
+import { test, expect, waitForHydration, type CDPSession, type Page } from "./fixtures/test";
 
 // Reuses the virtual-authenticator + register helpers from auth.test.ts.
 // Inlined rather than factored out to keep this file independently runnable.
@@ -19,6 +19,7 @@ async function setupVirtualAuthenticator(cdp: CDPSession) {
 async function registerUser(page: Page, email: string, username: string) {
   await page.goto("/auth/register");
   await expect(page.getByRole("heading", { name: "Register" })).toBeVisible();
+  await waitForHydration(page);
   await page.getByLabel("Email").fill(email);
   await page.getByLabel("Username").fill(username);
   await page.getByRole("checkbox").check();

e2e/social.test.ts

@@ -1,4 +1,4 @@
-import { test, expect, type CDPSession, type Page } from "./fixtures/test";
+import { test, expect, waitForHydration, type CDPSession, type Page } from "./fixtures/test";
 
 // Inline virtual-authenticator + register helpers, mirroring the pattern
 // in auth.test.ts / public-content.test.ts so this file runs standalone.
@@ -19,6 +19,7 @@ async function setupVirtualAuthenticator(cdp: CDPSession) {
 async function registerUser(page: Page, email: string, username: string) {
   await page.goto("/auth/register");
   await expect(page.getByRole("heading", { name: "Register" })).toBeVisible();
+  await waitForHydration(page);
   await page.getByLabel("Email").fill(email);
   await page.getByLabel("Username").fill(username);
   await page.getByRole("checkbox").check();