add numCtx (Context Window) setting to SESSION panel

- IChatSession/IChatTurn interfaces: add optional numCtx field
- Mongoose schemas: add numCtx field to ChatSession and ChatTurn
- API controller: validate numCtx (>=16384, multiple of 8192)
- ChatSessionService: persist numCtx on session, pass through to turn
- SessionPanel: add range slider for Context Window (hidden for OpenAI)
- Drone buildDroneModelConfig: prefer turn.numCtx over model defaults

gadget-code/frontend/src/components/SessionPanel.tsx

@@ -1,4 +1,4 @@
-import { ChatSessionMode, type AiProvider, type ChatSession } from '../lib/api';
+import { ChatSessionMode, type AiProvider, type ChatSession, type AiModel } from '../lib/api';
 import { WorkspaceMode } from '../lib/types';
 import WorkspaceModeIndicator from './WorkspaceModeIndicator';
 
@@ -10,6 +10,7 @@ interface SessionPanelProps {
   selectedProviderId: string;
   selectedModelId: string;
   sessionReasoningEffort: string;
+  sessionNumCtx: number;
   isEditingProvider: boolean;
   editProviderId: string;
   editModelId: string;
@@ -19,9 +20,12 @@ interface SessionPanelProps {
   isUpdatingName: boolean;
   isUpdatingMode: boolean;
   isUpdatingReasoning: boolean;
+  isUpdatingNumCtx: boolean;
   onWorkspaceModeChange: (mode: WorkspaceMode) => void;
   onModeChange: (e: React.ChangeEvent<HTMLSelectElement>) => void;
   onReasoningChange: (e: React.ChangeEvent<HTMLSelectElement>) => void;
+  onNumCtxChange: (e: React.ChangeEvent<HTMLInputElement>) => void;
+  onNumCtxCommit: (e: React.MouseEvent<HTMLInputElement> | React.TouchEvent<HTMLInputElement>) => void;
   onStartEditProvider: () => void;
   onSaveProvider: () => void;
   onCancelEditProvider: () => void;
@@ -36,6 +40,7 @@ interface SessionPanelProps {
   getSortedModels: (providerId: string) => AiProvider['models'];
   truncateModelName: (name: string, maxLength?: number) => string;
   getSelectedModelCapabilities: () => { hasThinking: boolean } | null;
+  getSelectedModel: () => AiModel | null;
 }
 
 export default function SessionPanel({
@@ -46,6 +51,7 @@ export default function SessionPanel({
   selectedProviderId,
   selectedModelId,
   sessionReasoningEffort,
+  sessionNumCtx,
   isEditingProvider,
   editProviderId,
   editModelId,
@@ -55,9 +61,12 @@ export default function SessionPanel({
   isUpdatingName,
   isUpdatingMode,
   isUpdatingReasoning,
+  isUpdatingNumCtx,
   onWorkspaceModeChange,
   onModeChange,
   onReasoningChange,
+  onNumCtxChange,
+  onNumCtxCommit,
   onStartEditProvider,
   onSaveProvider,
   onCancelEditProvider,
@@ -72,6 +81,7 @@ export default function SessionPanel({
   getSortedModels,
   truncateModelName,
   getSelectedModelCapabilities,
+  getSelectedModel,
 }: SessionPanelProps) {
   return (
     <div className="border-b border-border-subtle shrink-0">
@@ -261,6 +271,27 @@ export default function SessionPanel({
             <option value="high">High</option>
           </select>
         </div>
+        {providers.find(p => p._id === selectedProviderId)?.apiType !== 'openai' && (
+          <div>
+            <div className="text-xs text-text-muted">Context Window</div>
+            <div className="flex items-center gap-2 mt-1">
+              <input
+                type="range"
+                min={16384}
+                max={getSelectedModel()?.contextWindow || 131072}
+                step={8192}
+                value={sessionNumCtx}
+                onChange={onNumCtxChange}
+                onMouseUp={onNumCtxCommit}
+                onTouchEnd={onNumCtxCommit}
+                className="flex-1 h-2 bg-bg-tertiary rounded appearance-none cursor-pointer accent-brand"
+              />
+              <span className="text-xs text-text-secondary w-16 text-right tabular-nums">
+                {sessionNumCtx.toLocaleString()}
+              </span>
+            </div>
+          </div>
+        )}
       </div>
     </div>
   );

gadget-code/frontend/src/lib/api.ts

@@ -358,6 +358,7 @@ export interface ChatSession {
   provider: string | AiProvider;
   selectedModel: string;
   reasoningEffort?: string;
+  numCtx?: number;
   stats: ChatSessionStats;
   pins: Array<{ _id?: string; content: string }>;
 }
@@ -421,6 +422,7 @@ export interface ChatTurn {
   session: string | ChatSession;
   provider: string | AiProvider;
   llm: string;
+  numCtx?: number;
   mode: ChatSessionMode;
   status: "processing" | "finished" | "aborted" | "error";
   prompts: ChatTurnPrompts;

gadget-code/frontend/src/pages/ChatSessionView.tsx

@@ -68,6 +68,8 @@ export default function ChatSessionView() {
   const [selectedProviderId, setSelectedProviderId] = useState<string>('');
   const [selectedModelId, setSelectedModelId] = useState<string>('');
   const [sessionReasoningEffort, setSessionReasoningEffort] = useState<string>('off');
+  const [sessionNumCtx, setSessionNumCtx] = useState<number>(131072);
+  const [isUpdatingNumCtx, setIsUpdatingNumCtx] = useState(false);
   const [isEditingProvider, setIsEditingProvider] = useState(false);
   const [editProviderId, setEditProviderId] = useState('');
   const [editModelId, setEditModelId] = useState('');
@@ -214,6 +216,15 @@ export default function ChatSessionView() {
         setSelectedProviderId(providerId || '');
         setSelectedModelId(sessionData.selectedModel || '');
         setSessionReasoningEffort(sessionData.reasoningEffort || 'off');
+
+        // Initialize numCtx: persisted value wins, otherwise model's contextWindow
+        if (sessionData.numCtx) {
+          setSessionNumCtx(sessionData.numCtx);
+        } else {
+          const provider = allProviders.find(p => p._id === providerId);
+          const model = provider?.models.find(m => m.id === sessionData.selectedModel);
+          setSessionNumCtx(model?.contextWindow || 131072);
+        }
         
         // Set connection state to connecting - will update on socket connect
         setConnectionState('connecting');
@@ -793,13 +804,16 @@ export default function ChatSessionView() {
     }
   };
 
-  const getSelectedModelCapabilities = useCallback(() => {
+  const getSelectedModel = useCallback(() => {
     const provider = providers.find(p => p._id === selectedProviderId);
     if (!provider) return null;
-    const model = provider.models.find(m => m.id === selectedModelId);
+    return provider.models.find(m => m.id === selectedModelId) || null;
-    return model?.capabilities || null;
   }, [providers, selectedProviderId, selectedModelId]);
 
+  const getSelectedModelCapabilities = useCallback(() => {
+    return getSelectedModel()?.capabilities || null;
+  }, [getSelectedModel]);
+
   const handleReasoningChange = async (e: React.ChangeEvent<HTMLSelectElement>) => {
     if (!session) return;
 
@@ -821,6 +835,28 @@ export default function ChatSessionView() {
     }
   };
 
+  const handleNumCtxChange = (e: React.ChangeEvent<HTMLInputElement>) => {
+    setSessionNumCtx(parseInt(e.target.value, 10));
+  };
+
+  const handleNumCtxCommit = async (e: React.MouseEvent<HTMLInputElement> | React.TouchEvent<HTMLInputElement>) => {
+    if (!session || isUpdatingNumCtx) return;
+
+    const newValue = parseInt(e.currentTarget.value, 10);
+    setIsUpdatingNumCtx(true);
+    try {
+      const updatedSession = await chatSessionApi.update(session._id, {
+        numCtx: newValue
+      });
+      setSession(updatedSession);
+      showToast(`Context window set to ${newValue.toLocaleString()}`);
+    } catch (err) {
+      showToast(`Failed to change context window: ${err instanceof Error ? err.message : 'Unknown error'}`);
+    } finally {
+      setIsUpdatingNumCtx(false);
+    }
+  };
+
   const getProviderName = (id: string) => {
     return providers.find(p => p._id === id)?.name ?? 'None';
   };
@@ -859,6 +895,13 @@ export default function ChatSessionView() {
       setSession(updatedSession);
       setSelectedProviderId(editProviderId);
       setSelectedModelId(editModelId);
+
+      // Reset numCtx to new model's max context window
+      const newProvider = providers.find(p => p._id === editProviderId);
+      const newModel = newProvider?.models.find(m => m.id === editModelId);
+      const newMaxCtx = newModel?.contextWindow || 131072;
+      setSessionNumCtx(newMaxCtx);
+
       setIsEditingProvider(false);
       showToast('Provider and model updated');
     } catch (err) {
@@ -1173,6 +1216,7 @@ export default function ChatSessionView() {
           selectedProviderId={selectedProviderId}
           selectedModelId={selectedModelId}
           sessionReasoningEffort={sessionReasoningEffort}
+          sessionNumCtx={sessionNumCtx}
           isEditingProvider={isEditingProvider}
           editProviderId={editProviderId}
           editModelId={editModelId}
@@ -1182,9 +1226,12 @@ export default function ChatSessionView() {
           isUpdatingName={isUpdatingName}
           isUpdatingMode={isUpdatingMode}
           isUpdatingReasoning={isUpdatingReasoning}
+          isUpdatingNumCtx={isUpdatingNumCtx}
           onWorkspaceModeChange={handleWorkspaceModeChange}
           onModeChange={handleModeChange}
           onReasoningChange={handleReasoningChange}
+          onNumCtxChange={handleNumCtxChange}
+          onNumCtxCommit={handleNumCtxCommit}
           onStartEditProvider={handleStartEditProvider}
           onSaveProvider={handleSaveProvider}
           onCancelEditProvider={handleCancelEditProvider}
@@ -1199,6 +1246,7 @@ export default function ChatSessionView() {
           getSortedModels={getSortedModels}
           truncateModelName={truncateModelName}
           getSelectedModelCapabilities={getSelectedModelCapabilities}
+          getSelectedModel={getSelectedModel}
         />
 
         <ProjectPanel

gadget-code/src/controllers/api/v1/chat-session.ts

@@ -179,6 +179,7 @@ class ChatSessionController extends DtpController {
         selectedModel: string;
         mode: ChatSessionMode;
         reasoningEffort: "off" | "low" | "medium" | "high";
+        numCtx: number;
       }> = {};
 
       if (updates.name !== undefined) {
@@ -204,6 +205,12 @@ class ChatSessionController extends DtpController {
         }
         allowedUpdates.reasoningEffort = updates.reasoningEffort;
       }
+      if (updates.numCtx !== undefined) {
+        if (typeof updates.numCtx !== "number" || !Number.isInteger(updates.numCtx) || updates.numCtx < 16384 || updates.numCtx % 8192 !== 0) {
+          throw new Error(`Invalid numCtx: ${updates.numCtx}. Must be an integer >= 16384 and a multiple of 8192.`);
+        }
+        allowedUpdates.numCtx = updates.numCtx;
+      }
 
       const session = await ChatSessionService.update(
         res.locals.chatSession._id,

gadget-code/src/models/chat-session.ts

@@ -30,6 +30,7 @@ export const ChatSessionSchema = new Schema<IChatSession>({
     enum: ["off", "low", "medium", "high"],
     default: "off",
   },
+  numCtx: { type: Number },
   stats: {
     turnCount: { type: Number, default: 0, required: true },
     toolCallCount: { type: Number, default: 0, required: true },

gadget-code/src/models/chat-turn.ts

@@ -69,6 +69,7 @@ export const ChatTurnSchema = new Schema<IChatTurn>({
     enum: ["off", "low", "medium", "high"],
     default: "off",
   },
+  numCtx: { type: Number },
   mode: {
     type: String,
     enum: ChatSessionMode,

gadget-code/src/services/chat-session.ts

@@ -202,6 +202,7 @@ class ChatSessionService extends DtpService {
       selectedModel: string;
       mode: ChatSessionMode;
       reasoningEffort: ReasoningEffort;
+      numCtx: number;
     }>,
   ): Promise<IChatSession> {
     const session = await ChatSession.findById(chatSessionId);
@@ -230,6 +231,9 @@ class ChatSessionService extends DtpService {
     if (updates.reasoningEffort !== undefined) {
       session.reasoningEffort = updates.reasoningEffort;
     }
+    if (updates.numCtx !== undefined) {
+      session.numCtx = updates.numCtx;
+    }
 
     await session.save();
 
@@ -276,6 +280,7 @@ class ChatSessionService extends DtpService {
       provider: session.provider,
       llm: session.selectedModel,
       reasoningEffort: (session as IChatSession).reasoningEffort || "off",
+      numCtx: (session as IChatSession).numCtx,
       mode: session.mode,
       status: ChatTurnStatus.Processing,
       prompts: {

gadget-drone/src/services/agent.ts

@@ -218,7 +218,7 @@ class AgentService extends GadgetService {
           try {
             response = await AiService.chat(
               turn.provider,
-              this.buildDroneModelConfig(turn.provider, turn.llm, currentReasoning),
+              this.buildDroneModelConfig(turn.provider, turn.llm, currentReasoning, turn.numCtx),
               chatOptions,
               this.makeStreamHandler(socket),
             );
@@ -474,6 +474,7 @@ class AgentService extends GadgetService {
     provider: IAiProvider | GadgetId,
     modelId: string,
     reasoning: boolean | "low" | "medium" | "high",
+    numCtxOverride?: number,
   ): Omit<IDroneModelConfig, "provider"> {
     const settings = this.getModelSettings(provider, modelId);
     return {
@@ -484,7 +485,7 @@ class AgentService extends GadgetService {
         topP: settings?.topP ?? 0.9,
         topK: settings?.topK ?? 40,
         numPredict: settings?.numPredict ?? -1,         // -1 = unlimited (Ollama)
-        numCtx: settings?.numCtx ?? 131072,             // 128k fallback
+        numCtx: numCtxOverride ?? settings?.numCtx ?? 131072, // session override > model settings > 128k fallback
         maxCompletionTokens: settings?.maxCompletionTokens ?? 16384, // 16k fallback
       },
     };
@@ -626,7 +627,7 @@ class AgentService extends GadgetService {
 
         const response = await AiService.chat(
           provider,
-          this.buildDroneModelConfig(provider, turn.llm, false),
+          this.buildDroneModelConfig(provider, turn.llm, false, turn.numCtx),
           chatOptions,
           streamHandler,
         );

packages/api/src/interfaces/chat-session.ts

@@ -35,6 +35,7 @@ export interface IChatSession {
   provider: IAiProvider | GadgetId;
   selectedModel: string;
   reasoningEffort?: ReasoningEffort;
+  numCtx?: number;
   stats: {
     turnCount: number;
     toolCallCount: number;

packages/api/src/interfaces/chat-turn.ts

@@ -86,6 +86,7 @@ export interface IChatTurn {
   provider: IAiProvider | GadgetId;
   llm: string; // id/name of the model used to process the prompt
   reasoningEffort?: ReasoningEffort;
+  numCtx?: number;
   mode: ChatSessionMode;
   status: ChatTurnStatus;
   prompts: IChatTurnPrompts;