fix(auth): consume a verification token that arrives without a page load (E9.5 S2)

Found in UAT. Navigating a tab that already runs the app to a URL differing only in
the fragment is a same-document navigation: nothing reloads, so the import-time entry
snapshot never sees the token. It sat unconsumed in the address bar and the previous
outcome stayed on screen -- the same silence this sprint set out to remove, wearing a
different hat. Pasting the emailed link into a running tab does exactly this, and our
verification mails were plain text until 0.78.8, which makes pasting the normal way to
use one.

A hashchange listener now picks up the new token, the guard tracks consumed tokens
rather than a single fired flag (still exactly one POST per token), and a fresh link
clears the standing outcome instead of leaving the old banner up.

frontend/src/lib/useVerifyEntry.ts

@@ -24,21 +24,42 @@ export type VerifyEntry = {
  * the fragment was then stripped, and the user got no signal at all — the link simply did nothing.
  * Incognito worked, which is why it survived so long.
  *
- * Fires exactly once. The token is single-use, so a second POST (a StrictMode remount, any re-render)
- * would 400 and wrongly flip a successful confirmation to "invalid".
+ * The link does not always arrive as a page LOAD. When the app is already open in the tab and the URL
+ * differs only in the fragment, the browser performs a same-document navigation — no reload, so the
+ * import-time snapshot never sees the new token. Pasting the emailed link into a running tab's address
+ * bar does exactly that, and our verification mails were plain text until 0.78.8, which makes pasting
+ * the normal way to use one. Without the `hashchange` listener below the token would sit unconsumed in
+ * the address bar: the same silence signed-in users met before, in a second disguise.
+ *
+ * Each token is posted exactly once. It is single-use, so a repeat POST (a StrictMode remount, any
+ * re-render) would 400 and wrongly flip a successful confirmation to "invalid".
  */
 export function useVerifyEntry(): VerifyEntry {
-  const token = entryHash.get("verify");
+  const [token, setToken] = useState<string | null>(() => entryHash.get("verify"));
   const [outcome, setOutcome] = useState<VerifyOutcome | null>(null);
   const [email, setEmail] = useState<string | null>(null);
-  const fired = useRef(false);
+  const consumed = useRef(new Set<string>());
+
+  useEffect(() => {
+    const onHashChange = () => {
+      const next = new URLSearchParams(window.location.hash.replace(/^#/, "")).get("verify");
+      if (next) setToken(next);
+    };
+    // replaceState (how clearEntryUrl strips the fragment) does NOT fire hashchange, so this cannot
+    // feed itself.
+    window.addEventListener("hashchange", onHashChange);
+    return () => window.removeEventListener("hashchange", onHashChange);
+  }, []);
 
   useEffect(() => {
     // Clear the address bar even with no token to consume: a `#reset=` fragment opened in a
     // signed-in browser is equally spent, and leaving either in history re-sends it on a reload.
     clearEntryUrl();
-    if (!token || fired.current) return;
-    fired.current = true;
+    if (!token || consumed.current.has(token)) return;
+    consumed.current.add(token);
+    // A second link arriving over an unread first outcome must not leave the OLD banner standing.
+    setOutcome(null);
+    setEmail(null);
     api
       .verifyEmail(token)
       .then((r) => {

frontend/src/lib/verifyEntry.dom.test.tsx

@@ -85,3 +85,52 @@ describe("confirming an emailed verification link", () => {
     expect(window.location.hash).toBe("");
   });
 });
+
+// The link does not always arrive as a page LOAD. Found in UAT on 2026-09-03: navigating a tab that
+// already runs the app to a URL differing only in the fragment is a same-document navigation, so
+// nothing reloads, the import-time snapshot never sees the token, and it sat unconsumed in the
+// address bar — the same silence the sprint set out to remove, wearing a different hat.
+describe("a verification link that arrives as a fragment-only navigation", () => {
+  it("consumes a token delivered by hashchange, and clears it from the address bar", async () => {
+    const verifyEmail = vi.fn().mockResolvedValue({ ok: true, email: "pasted@example.com" });
+    const outcome = await mountAt("/", verifyEmail);
+    expect(verifyEmail).not.toHaveBeenCalled();
+
+    await act(async () => {
+      window.history.replaceState(null, "", "/#verify=pasted-token");
+      window.dispatchEvent(new HashChangeEvent("hashchange"));
+    });
+
+    expect(verifyEmail).toHaveBeenCalledWith("pasted-token");
+    expect(outcome()).toBe("ok:pasted@example.com");
+    expect(window.location.hash).toBe("");
+  });
+
+  it("replaces a standing outcome rather than leaving the previous banner up", async () => {
+    const verifyEmail = vi
+      .fn()
+      .mockResolvedValueOnce({ ok: true, email: "first@example.com" })
+      .mockRejectedValueOnce(new Error("400"));
+    const outcome = await mountAt("/#verify=first-token", verifyEmail);
+    expect(outcome()).toBe("ok:first@example.com");
+
+    await act(async () => {
+      window.history.replaceState(null, "", "/#verify=spent-token");
+      window.dispatchEvent(new HashChangeEvent("hashchange"));
+    });
+
+    expect(outcome()).toBe("invalid:-");
+  });
+
+  it("posts a given token once even if the same fragment arrives again", async () => {
+    const verifyEmail = vi.fn().mockResolvedValue({ ok: true, email: "same@example.com" });
+    await mountAt("/#verify=same-token", verifyEmail);
+
+    await act(async () => {
+      window.history.replaceState(null, "", "/#verify=same-token");
+      window.dispatchEvent(new HashChangeEvent("hashchange"));
+    });
+
+    expect(verifyEmail).toHaveBeenCalledTimes(1);
+  });
+});