master planner: preserve state across mode switches

switchMode was resetting messages/proposal/swarm/runSteps/etc. every
time. Now it snapshots the current mode's slice into a ref before
loading the target mode's snapshot (or a fresh slice if the target
was never visited). Switching specialists → swarm → specialists keeps
the specialists chat intact.

Also route async /planner/chat responses to the mode the message was
sent in, not the currently-active mode — user can switch modes while
the reply is in flight without the assistant response landing in the
wrong chat.

frontend/src/components/dashboard/MasterPlannerModal.tsx

@@ -51,10 +51,38 @@ async function readSse(url: string, body: unknown, onEvt: (e: Record<string, unk
   }
 }
 
+// Per-mode chat/proposal state so switching modes preserves what was there.
+// Kept in a ref (not state) — restore reads it during switchMode and immediately
+// pushes into the individual setters below, so React re-renders once.
+type ModeSlice = {
+  messages: Msg[];
+  input: string;
+  proposal: Proposal | null;
+  swarm: SwarmSpec | null;
+  runSteps: Step[];
+  runStatus: string | null;
+  runFinal: string | null;
+  webhookUrl: string | null;
+  buildProg: { pct: number; label: string } | null;
+  error: string | null;
+};
+const emptySlice = (m: Mode): ModeSlice => ({
+  messages: [{ role: "planner", content: INTRO[m] }],
+  input: "",
+  proposal: null,
+  swarm: null,
+  runSteps: [],
+  runStatus: null,
+  runFinal: null,
+  webhookUrl: null,
+  buildProg: null,
+  error: null,
+});
+
 export function MasterPlannerModal({ onClose }: { onClose: () => void }) {
   const router = useRouter();
   const [mode, setMode] = useState<Mode>("specialists");
-  const [messages, setMessages] = useState<Msg[]>([{ role: "planner", content: INTRO.specialists }]);
+  const [messages, setMessages] = useState<Msg[]>(() => emptySlice("specialists").messages);
   const [input, setInput] = useState("");
   const [thinking, setThinking] = useState(false);
   const [proposal, setProposal] = useState<Proposal | null>(null);
@@ -69,6 +97,8 @@ export function MasterPlannerModal({ onClose }: { onClose: () => void }) {
   const [runFinal, setRunFinal] = useState<string | null>(null);
   const scrollRef = useRef<HTMLDivElement>(null);
   const esRef = useRef<EventSource | null>(null);
+  const snapshotsRef = useRef<Partial<Record<Mode, ModeSlice>>>({});
+  const modeRef = useRef<Mode>("specialists");
 
   useEffect(() => { const onKey = (e: KeyboardEvent) => { if (e.key === "Escape") onClose(); }; window.addEventListener("keydown", onKey); return () => window.removeEventListener("keydown", onKey); }, [onClose]);
   useEffect(() => { scrollRef.current?.scrollTo({ top: 1e9, behavior: "smooth" }); }, [messages, thinking]);
@@ -77,23 +107,64 @@ export function MasterPlannerModal({ onClose }: { onClose: () => void }) {
   function switchMode(m: Mode) {
     if (m === mode) return;
     esRef.current?.close();
-    setMode(m); setMessages([{ role: "planner", content: INTRO[m] }]); setInput("");
-    setProposal(null); setSwarm(null); setError(null); setBuildProg(null); setWebhookUrl(null);
-    setRunSteps([]); setRunStatus(null); setRunFinal(null);
+    // Snapshot the current mode before we blow it away.
+    snapshotsRef.current[mode] = {
+      messages, input, proposal, swarm, runSteps, runStatus, runFinal, webhookUrl, buildProg, error,
+    };
+    const next = snapshotsRef.current[m] ?? emptySlice(m);
+    setMode(m);
+    modeRef.current = m;
+    setMessages(next.messages);
+    setInput(next.input);
+    setProposal(next.proposal);
+    setSwarm(next.swarm);
+    setRunSteps(next.runSteps);
+    setRunStatus(next.runStatus);
+    setRunFinal(next.runFinal);
+    setWebhookUrl(next.webhookUrl);
+    setBuildProg(next.buildProg);
+    setError(next.error);
+    setThinking(false);
+    setBuilding(false);
   }
 
   async function send() {
     const text = input.trim();
     if (!text || thinking) return;
+    const originMode = mode;
     const next: Msg[] = [...messages, { role: "user", content: text }];
     setMessages(next); setInput(""); setThinking(true); setError(null);
+    // Route async writes to the mode the message was sent in — user may switch
+    // mid-flight; without this the reply lands in the wrong chat.
+    const routeMessages = (updater: (prev: Msg[]) => Msg[]) => {
+      if (modeRef.current === originMode) {
+        setMessages(updater);
+      } else {
+        const snap = snapshotsRef.current[originMode] ?? emptySlice(originMode);
+        snapshotsRef.current[originMode] = { ...snap, messages: updater(snap.messages) };
+      }
+    };
+    const routeProposal = (p: Proposal) => {
+      if (modeRef.current === originMode) setProposal(p);
+      else {
+        const snap = snapshotsRef.current[originMode] ?? emptySlice(originMode);
+        snapshotsRef.current[originMode] = { ...snap, proposal: p };
+      }
+    };
+    const routeSwarm = (sp: SwarmSpec) => {
+      if (modeRef.current === originMode) setSwarm(sp);
+      else {
+        const snap = snapshotsRef.current[originMode] ?? emptySlice(originMode);
+        snapshotsRef.current[originMode] = { ...snap, swarm: sp };
+      }
+    };
     try {
-      await readSse("/api/planner/chat", { mode, messages: next.map((m) => ({ role: m.role === "user" ? "user" : "assistant", content: m.content })) }, (e) => {
+      await readSse("/api/planner/chat", { mode: originMode, messages: next.map((m) => ({ role: m.role === "user" ? "user" : "assistant", content: m.content })) }, (e) => {
         if (e.stage === "error") setError(String(e.label || "error"));
         else if (e.stage === "done") {
-          if (e.reply) setMessages((m) => [...m, { role: "planner", content: String(e.reply) }]);
-          if (e.proposal) setProposal(e.proposal as Proposal);
-          if (e.swarm) setSwarm(e.swarm as SwarmSpec);
+          if (e.reply) routeMessages((m) => [...m, { role: "planner", content: String(e.reply) }]);
+          if (e.proposal) routeProposal(e.proposal as Proposal);
+          if (e.swarm) routeSwarm(e.swarm as SwarmSpec);
         }
       });
     } catch { setError("Network error"); }