diff --git a/web/shared.ts b/web/shared.ts
index d154d4a..b9090a3 100644
--- a/web/shared.ts
+++ b/web/shared.ts
@@ -1,6 +1,6 @@
 import { useParams } from 'react-router';
 
-// Which email is open is `/email/:emailId`. The route pair already existed, but the URL was a mirror
+// Which email is open is `/email/:id`. The route pair already existed, but the URL was a mirror
 // rather than the state: the selection lived in an `EMAIL_SELECTED` global and two effects copied it
 // back and forth with the route. That round-trip is what kept a row a `<button>` — nothing to link to,
 // no cmd-click, no middle-click — and it meant Back raced the effect that had just written the URL
@@ -9,5 +9,20 @@ import { useParams } from 'react-router';
 /** `search` carries the folder you are reading in (`?folder=sent`), which a bare pathname would drop. */
 export const emailPath = (id: string, search = '') => `/email/${encodeURIComponent(id)}${search}`;
 
-/** The open email, or null on the bare `/email` route — which is a real state, not one to redirect away. */
-export const useSelectedEmailId = (): string | null => useParams<{ emailId?: string }>().emailId ?? null;
+/**
+ * The open email, or null on the bare `/email` route — which is a real state, not one to redirect away.
+ *
+ * ── Why it reads `section` ──
+ *
+ * This asked for `emailId` while email was part of the platform and had its own `/email/:emailId` route.
+ * A plugin does not declare its routes: the platform mounts every one at `<route>` and `<route>/:section`,
+ * so the param arrives under the platform's name whatever the plugin means by it. Asking for `emailId`
+ * got `undefined` from the day email became a plugin — the reader then had no selection to show and sat on
+ * "Select an email to read" however many messages you clicked, with the list and the API both working.
+ *
+ * `emailId` is still accepted so the hook keeps working if this ever mounts under its own route again.
+ */
+export const useSelectedEmailId = (): string | null => {
+  const params = useParams<{ section?: string; emailId?: string }>();
+  return params.emailId ?? params.section ?? null;
+};