Merge bug/messaging-stale-thread-on-account-switch

Fix: switching accounts no longer lands the new user on a stale chat thread inherited
from the previous account (an empty self-thread where new messages never appeared).
Clear _sub/_ov from history.state before the switch reload + guard partnerId===meId.
User-confirmed on localdev with two real accounts.

frontend/src/components/Messages.tsx

@@ -22,7 +22,9 @@ export default function Messages({ meId }: { meId: number }) {
   // the module (open() pushes an entry; back() = history.back()).
   const { view, open, back } = useHistorySubview<View>("list");
 
-  if (typeof view === "object") {
+  // Guard against a stale sub-view whose partnerId is the current user's own id (you can't
+  // message yourself). This can be inherited across an account switch — fall back to the list.
+  if (typeof view === "object" && view.partnerId !== meId) {
     return (
       <PageThread
         meId={meId}

frontend/src/components/NavSidebar.tsx

@@ -112,6 +112,14 @@ export default function NavSidebar({
   async function switchTo(id: number) {
     try {
       await api.switchAccount(id);
+      // Drop the previous account's in-module sub-view/overlay before the reload (which would
+      // otherwise preserve history.state across the swap). Otherwise the new account lands on a
+      // stale sub-view — e.g. an open chat thread whose partnerId belongs to the OLD identity
+      // (often the new account's own id → an empty self-thread). Start at the module root instead.
+      const st = { ...(window.history.state || {}) };
+      delete st._sub;
+      delete st._ov;
+      window.history.replaceState(st, "");
       location.reload(); // cleanest way to reload all per-user state for the new account
     } catch {
       /* a revoked/removed account — leave the popover open */