feat(FN-1741): add memory compaction feature

- Add MemoryCompaction service in core for compacting agent memory stores
- Add POST /api/memory/compact route handler in dashboard server
- Add compactMemory frontend API wrapper in dashboard app
- Add Compact Memory button to SettingsModal UI
- Add comprehensive tests for the compaction service and routes

packages/dashboard/app/components/SettingsModal.tsx

@@ -2,7 +2,7 @@ import { useState, useEffect, useCallback, useRef } from "react";
 import { Globe, Folder } from "lucide-react";
 import { THINKING_LEVELS, PROMPT_KEY_CATALOG, isGlobalSettingsKey, isProjectSettingsKey } from "@fusion/core";
 import type { Settings, GlobalSettings, ThemeMode, ColorTheme, ModelPreset, NtfyNotificationEvent, PromptKey, AgentPromptsConfig } from "@fusion/core";
-import { fetchSettings, fetchSettingsByScope, updateSettings, updateGlobalSettings, fetchAuthStatus, loginProvider, logoutProvider, saveApiKey, clearApiKey, fetchModels, testNtfyNotification, fetchBackups, createBackup, exportSettings, importSettings, fetchMemory, saveMemory, fetchGlobalConcurrency, updateGlobalConcurrency } from "../api";
+import { fetchSettings, fetchSettingsByScope, updateSettings, updateGlobalSettings, fetchAuthStatus, loginProvider, logoutProvider, saveApiKey, clearApiKey, fetchModels, testNtfyNotification, fetchBackups, createBackup, exportSettings, importSettings, fetchMemory, saveMemory, fetchGlobalConcurrency, updateGlobalConcurrency, compactMemory } from "../api";
 import type { AuthProvider, ModelInfo, BackupListResponse, SettingsExportData, MemoryBackendCapabilities } from "../api";
 import { useMemoryBackendStatus } from "../hooks/useMemoryBackendStatus";
 import type { ToastType } from "../hooks/useToast";
@@ -151,6 +151,7 @@ export function SettingsModal({
   const [memoryContent, setMemoryContent] = useState("");
   const [memoryLoading, setMemoryLoading] = useState(false);
   const [memoryDirty, setMemoryDirty] = useState(false);
+  const [compactLoading, setCompactLoading] = useState(false);
 
   // Global concurrency state
   const [globalMaxConcurrent, setGlobalMaxConcurrent] = useState<number | undefined>(4);
@@ -777,6 +778,20 @@ export function SettingsModal({
     }
   }, [memoryContent, projectId, addToast]);
 
+  const handleCompactMemory = useCallback(async () => {
+    setCompactLoading(true);
+    try {
+      const { content } = await compactMemory(projectId);
+      setMemoryContent(content);
+      setMemoryDirty(true);
+      addToast("Memory compacted successfully", "success");
+    } catch (err: any) {
+      addToast(err?.message || "Failed to compact memory", "error");
+    } finally {
+      setCompactLoading(false);
+    }
+  }, [projectId, addToast]);
+
   const savePresetDraft = () => {
     if (!presetDraft) return;
 
@@ -2072,6 +2087,19 @@ export function SettingsModal({
                 <small className="field-error">Cannot save: {isMemoryEnabled ? "Backend is read-only" : "Memory is disabled"}</small>
               </div>
             )}
+
+            {isEditingAllowed && (
+              <div className="form-group">
+                <button
+                  type="button"
+                  className="btn btn-secondary btn-sm"
+                  onClick={handleCompactMemory}
+                  disabled={compactLoading}
+                >
+                  {compactLoading ? "Compacting…" : "Compact Memory"}
+                </button>
+              </div>
+            )}
           </>
         );
       }

packages/dashboard/app/components/__tests__/SettingsModal.test.tsx

@@ -70,6 +70,7 @@ vi.mock("../../api", () => ({
   importSettings: vi.fn(() => Promise.resolve({ success: true, globalCount: 0, projectCount: 0 })),
   fetchMemory: vi.fn(() => Promise.resolve({ content: "" })),
   saveMemory: vi.fn(() => Promise.resolve({ success: true })),
+  compactMemory: vi.fn(() => Promise.resolve({ content: "# Compacted Memory\n\nImportant content." })),
 }));
 
 // Mock useMemoryBackendStatus hook
@@ -3686,4 +3687,129 @@ describe("Prompts section", () => {
       expect(globalPayload.defaultModelId).toBeNull();
     });
   });
+
+  describe("Memory section - Compact Memory", () => {
+    it("renders Compact Memory button in memory section", async () => {
+      render(<SettingsModal onClose={onClose} addToast={addToast} />);
+      await waitFor(() => expect(fetchSettings).toHaveBeenCalled());
+
+      // Navigate to Memory section
+      const memorySection = screen.getByText("Memory");
+      fireEvent.click(memorySection);
+
+      await waitFor(() => {
+        // Should show Compact Memory button
+        expect(screen.getByText("Compact Memory")).toBeInTheDocument();
+      });
+    });
+
+    it("calls compactMemory when Compact Memory button is clicked", async () => {
+      const { compactMemory } = await import("../../api");
+      (compactMemory as ReturnType<typeof vi.fn>).mockResolvedValueOnce({
+        content: "# Compacted Memory\n\nImportant content.",
+      });
+
+      render(<SettingsModal onClose={onClose} addToast={addToast} />);
+      await waitFor(() => expect(fetchSettings).toHaveBeenCalled());
+
+      // Navigate to Memory section
+      const memorySection = screen.getByText("Memory");
+      fireEvent.click(memorySection);
+
+      await waitFor(() => {
+        // Click Compact Memory button
+        const compactBtn = screen.getByText("Compact Memory");
+        fireEvent.click(compactBtn);
+      });
+
+      await waitFor(() => {
+        expect(compactMemory).toHaveBeenCalled();
+      });
+    });
+
+    it("updates editor content after successful compaction", async () => {
+      const { compactMemory } = await import("../../api");
+      const newContent = "# Compacted Memory\n\nImportant content.";
+      (compactMemory as ReturnType<typeof vi.fn>).mockResolvedValueOnce({
+        content: newContent,
+      });
+
+      render(<SettingsModal onClose={onClose} addToast={addToast} />);
+      await waitFor(() => expect(fetchSettings).toHaveBeenCalled());
+
+      // Navigate to Memory section
+      const memorySection = screen.getByText("Memory");
+      fireEvent.click(memorySection);
+
+      await waitFor(() => {
+        // Click Compact Memory button
+        const compactBtn = screen.getByText("Compact Memory");
+        fireEvent.click(compactBtn);
+      });
+
+      await waitFor(() => {
+        // Should show success toast
+        expect(addToast).toHaveBeenCalledWith("Memory compacted successfully", "success");
+      });
+    });
+
+    it("disables button while compacting", async () => {
+      let resolveCompact: (value: { content: string }) => void;
+      const { compactMemory } = await import("../../api");
+      (compactMemory as ReturnType<typeof vi.fn>).mockImplementation(
+        () => new Promise((resolve) => { resolveCompact = resolve; })
+      );
+
+      render(<SettingsModal onClose={onClose} addToast={addToast} />);
+      await waitFor(() => expect(fetchSettings).toHaveBeenCalled());
+
+      // Navigate to Memory section
+      const memorySection = screen.getByText("Memory");
+      fireEvent.click(memorySection);
+
+      await waitFor(() => {
+        // Click Compact Memory button
+        const compactBtn = screen.getByText("Compact Memory");
+        fireEvent.click(compactBtn);
+      });
+
+      await waitFor(() => {
+        // Button should show loading text
+        expect(screen.getByText("Compacting…")).toBeInTheDocument();
+      });
+
+      // Complete the promise
+      resolveCompact!({ content: "# Compacted Memory\n\nImportant content." });
+
+      await waitFor(() => {
+        // Button should be back to normal
+        expect(screen.getByText("Compact Memory")).toBeInTheDocument();
+      });
+    });
+
+    it("shows error toast when compaction fails", async () => {
+      const { compactMemory } = await import("../../api");
+      (compactMemory as ReturnType<typeof vi.fn>).mockRejectedValueOnce(
+        new Error("AI service unavailable")
+      );
+
+      render(<SettingsModal onClose={onClose} addToast={addToast} />);
+      await waitFor(() => expect(fetchSettings).toHaveBeenCalled());
+
+      // Navigate to Memory section
+      const memorySection = screen.getByText("Memory");
+      fireEvent.click(memorySection);
+
+      await waitFor(() => {
+        // Click Compact Memory button
+        const compactBtn = screen.getByText("Compact Memory");
+        fireEvent.click(compactBtn);
+      });
+
+      await waitFor(() => {
+        // Should show error toast
+        expect(addToast).toHaveBeenCalledWith("AI service unavailable", "error");
+      });
+    });
+  });
 });