fix: RAG — UTF-8 chunk boundary, source dedupe, embed-model guard + reindex

- chunk(): byte splits that landed mid multibyte char silently dropped
  the whole chunk (accented/CJK lore). Back the boundary off to a char
  boundary; regression test included.
- add_document(): DELETE the source first — re-adding a file no longer
  doubles its chunks.
- chunks now record their embed_model (ALTER TABLE migration for old
  DBs); search skips chunks from a different model; rag_list reports it;
  new rag_reindex re-embeds everything, surfaced in the Lore panel as a
  mismatch banner with a one-click Reindex.

src/components/LorePanel.tsx

@@ -8,6 +8,7 @@ import { addToLore } from "../lib/lore";
 interface RagSource {
   source: string;
   chunks: number;
+  model: string;
 }
 
 interface RagHit {
@@ -39,8 +40,15 @@ export function LorePanel() {
   const [expanded, setExpanded] = useState<string | null>(null);
   const [chunks, setChunks] = useState<RagChunk[]>([]);
   const [loadingChunks, setLoadingChunks] = useState(false);
+  // ponytail: current embed model, to flag sources indexed with a different
+  // one (search skips those — garbage cosine scores). "" = still loading.
+  const [embedModel, setEmbedModel] = useState("");
+  const [reindexing, setReindexing] = useState(false);
   const { addToast } = useToast();
 
+  const stale =
+    embedModel !== "" && sources.some((s) => s.model !== "" && s.model !== embedModel);
+
   async function loadSources() {
     try {
       setSources(await invoke<RagSource[]>("rag_list"));
@@ -51,6 +59,9 @@ export function LorePanel() {
 
   useEffect(() => {
     loadSources();
+    invoke<{ embed_model: string }>("get_llm_config")
+      .then((c) => setEmbedModel(c.embed_model))
+      .catch(() => {});
   }, []);
 
   async function loadChunks(s: string) {
@@ -101,6 +112,18 @@ export function LorePanel() {
     loadSources();
   }
 
+  async function reindex() {
+    setReindexing(true);
+    try {
+      const r = await invoke<{ sources: number; chunks: number }>("rag_reindex");
+      addToast(`Reindexed ${r.sources} sources · ${r.chunks} chunks`, "success");
+      await loadSources();
+    } catch (e) {
+      addToast(`Reindex failed: ${e}`, "error");
+    }
+    setReindexing(false);
+  }
+
   // ponytail: file upload via native HTML input — no tauri-plugin-dialog
   // needed. Reads .md/.txt contents in the webview and indexes each file as
   // its own lore source. Multiple files supported.
@@ -214,6 +237,20 @@ export function LorePanel() {
         <div className="flex flex-col gap-2">
           <div className="flex items-center justify-between">
             <h3 className="font-heading text-[var(--color-gold-bright)] text-sm">Indexed Sources</h3>
+            {/* ponytail: embed-model mismatch banner — search silently skips
+                these chunks, so surface it with the one-click fix. */}
+            {stale && (
+              <div className="flex items-center gap-1.5">
+                <span className="text-[10px] text-[var(--color-gold-bright)]">Indexed with an old embedding model</span>
+                <button
+                  onClick={reindex}
+                  disabled={reindexing}
+                  className="rounded bg-[var(--color-gold-bright)] text-[var(--color-bg-deep)] px-2 py-0.5 text-[10px] font-semibold cursor-pointer disabled:opacity-50"
+                >
+                  {reindexing ? "Reindexing…" : "Reindex all"}
+                </button>
+              </div>
+            )}
             {sources.length > 0 && (
               confirmClear ? (
                 <div className="flex items-center gap-1">