feat(search): support from:username with no body text

Typing "from:jared" with no additional text now shows all cached
messages from that user across all rooms.

- SearchInput: call onSearch() even when only from: tokens were
  extracted (no remaining body text), passing an empty string term
- useLocalMessageSearch: introduce senderOnlyMode (empty term +
  senders set) which searches ALL rooms instead of encrypted-only,
  and skips text matching — just filters by sender
- MessageSearch: define hasActiveSearch / senderOnlyMode flags;
  use them to enable local search and fix placeholder/loading/results
  conditions; adapt local results section header and description

Server-side search is skipped in sender-only mode (Matrix search API
requires a search_term); results come from the local event cache.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/message-search/MessageSearch.tsx

@@ -213,12 +213,21 @@ export function MessageSearch({
     [msgSearchParams.rooms, searchPathSearchParams.global, allRooms, rooms],
   );
 
-  // Run synchronous client-side search over encrypted rooms immediately.
+  // term === undefined  → no search started
+  // term === ''         → sender-only search (from:user with no body text)
+  // term === 'foo'      → normal text search
+  const hasActiveSearch =
+    msgSearchParams.term !== undefined || !!msgSearchParams.senders?.length;
+  const senderOnlyMode = !msgSearchParams.term && !!msgSearchParams.senders?.length;
+
+  // Run synchronous client-side search immediately.
+  // In text-search mode: covers encrypted rooms only (server handles plaintext).
+  // In sender-only mode: covers all rooms (server has no sender-only search).
   // cacheVersion in deps so it re-runs after "Load more" paginates new events.
   const localResult = useMemo(() => {
-    if (!msgSearchParams.term) return null;
+    if (!hasActiveSearch) return null;
     return searchLocalMessages({
-      term: msgSearchParams.term,
+      term: msgSearchParams.term ?? '',
       roomIds: localSearchRooms,
       senders: msgSearchParams.senders,
     });
@@ -404,19 +413,19 @@ export function MessageSearch({
         />
       </Box>
 
-      {!msgSearchParams.term && status === 'pending' && (
+      {!hasActiveSearch && (
         <PageHeroEmpty>
           <PageHeroSection>
             <PageHero
               icon={<Icon size="600" src={Icons.Message} />}
               title="Search Messages"
-              subTitle="Find helpful messages in your community by searching with related keywords."
+              subTitle="Find helpful messages in your community by searching with related keywords, or type from:@user to see all messages from someone."
             />
           </PageHeroSection>
         </PageHeroEmpty>
       )}
 
-      {msgSearchParams.term && groups.length === 0 && status === 'success' && (
+      {hasActiveSearch && !senderOnlyMode && groups.length === 0 && status === 'success' && (
         <Box direction="Column" gap="200">
           <Box
             className={ContainerColor({ variant: 'Warning' })}
@@ -450,7 +459,7 @@ export function MessageSearch({
         </Box>
       )}
 
-      {((msgSearchParams.term && status === 'pending') ||
+      {((!senderOnlyMode && msgSearchParams.term && status === 'pending') ||
         (groups.length > 0 && vItems.length === 0)) && (
         <Box direction="Column" gap="100">
           {[...Array(8).keys()].map((key) => (
@@ -460,6 +469,7 @@ export function MessageSearch({
       )}
 
       {msgSearchParams.term &&
+        !senderOnlyMode &&
         localResult &&
         localResult.encryptedRoomsCount > 0 &&
         vItems.length > 0 && (
@@ -524,20 +534,24 @@ export function MessageSearch({
         </Box>
       )}
 
-      {localResult && localResult.encryptedRoomsCount > 0 && (
+      {localResult && (senderOnlyMode ? localResult.groups.length > 0 : localResult.encryptedRoomsCount > 0) && (
         <Box direction="Column" gap="300">
           <Box direction="Column" gap="200">
             <Box alignItems="Center" gap="200">
-              <Icon size="200" src={Icons.Lock} />
-              <Text size="H5">Encrypted Rooms</Text>
-              <Text size="T200" style={{ opacity: 0.55 }}>
-                {`${localResult.searchedRoomsCount} / ${localResult.encryptedRoomsCount} cached`}
-              </Text>
+              <Icon size="200" src={senderOnlyMode ? Icons.User : Icons.Lock} />
+              <Text size="H5">{senderOnlyMode ? 'Messages from user' : 'Encrypted Rooms'}</Text>
+              {!senderOnlyMode && (
+                <Text size="T200" style={{ opacity: 0.55 }}>
+                  {`${localResult.searchedRoomsCount} / ${localResult.encryptedRoomsCount} cached`}
+                </Text>
+              )}
             </Box>
             <Text size="T300" priority="300">
-              {localResult.groups.length > 0
-                ? `Showing locally cached messages from ${localResult.searchedRoomsCount} encrypted room${localResult.searchedRoomsCount !== 1 ? 's' : ''}. Load more history below to extend coverage.`
-                : `No matches in your local cache. Load messages below to search further back.`}
+              {senderOnlyMode
+                ? `Showing locally cached messages from this user across all rooms. Open more rooms or load history below to extend coverage.`
+                : localResult.groups.length > 0
+                  ? `Showing locally cached messages from ${localResult.searchedRoomsCount} encrypted room${localResult.searchedRoomsCount !== 1 ? 's' : ''}. Load more history below to extend coverage.`
+                  : `No matches in your local cache. Load messages below to search further back.`}
             </Text>
             <Line size="300" variant="Surface" />
           </Box>