feat: multiple UI improvements, font settings, and memory file display names (#175)

## Summary

- **fix**: `show_thinking_blocks` setting now persists across sessions — it was defined on the TypeScript side but missing from the Rust `HikariConfig` struct, so serde silently dropped it on every save/load
- **feat**: Tool calls are now rendered as collapsible blocks matching the Extended Thinking block aesthetic, replacing the old inline dropdown approach
- **feat**: Add configurable max output tokens setting
- **feat**: Use random creative names for conversation tabs
- **test**: Significantly expanded frontend unit test coverage
- **docs**: Require tests for all changes in CLAUDE.md
- **feat**: Allow users to specify a custom terminal font (Closes #176)
- **feat**: Display friendly names for memory files derived from the first heading (Closes #177)
- **feat**: Add custom UI font support for the app chrome (buttons, labels, tabs)
- **fix**: Apply custom UI font to the full app interface — `.app-container` was hardcoded, blocking inheritance from `body`; also renamed "Custom Font" to "Custom Terminal Font" for clarity

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #175
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src/lib/stores/config.test.ts

@@ -1,12 +1,20 @@
-import { describe, it, expect, beforeEach, vi } from "vitest";
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
+import { get } from "svelte/store";
 import {
   configStore,
   maskPaths,
   clampFontSize,
   applyFontSize,
+  applyCustomFont,
+  applyCustomUiFont,
   applyTheme,
   applyCustomThemeColors,
   clearCustomThemeColors,
+  isDarkTheme,
+  isStreamerMode,
+  isCompactMode,
+  shouldHidePaths,
+  showThinkingBlocks,
   MIN_FONT_SIZE,
   MAX_FONT_SIZE,
   DEFAULT_FONT_SIZE,
@@ -15,12 +23,17 @@ import {
   type CustomThemeColors,
 } from "./config";
 import { invoke } from "@tauri-apps/api/core";
+import { readFile } from "@tauri-apps/plugin-fs";
 
 // Mock Tauri APIs
 vi.mock("@tauri-apps/api/core", () => ({
   invoke: vi.fn(),
 }));
 
+vi.mock("@tauri-apps/plugin-fs", () => ({
+  readFile: vi.fn(),
+}));
+
 describe("config store", () => {
   describe("font size constants", () => {
     it("has correct MIN_FONT_SIZE", () => {
@@ -196,9 +209,14 @@ describe("config store", () => {
         show_thinking_blocks: true,
         use_worktree: false,
         disable_1m_context: false,
+        max_output_tokens: null,
         trusted_workspaces: [],
         background_image_path: null,
         background_image_opacity: 0.3,
+        custom_font_path: null,
+        custom_font_family: null,
+        custom_ui_font_path: null,
+        custom_ui_font_family: null,
       };
 
       expect(config.model).toBe("claude-sonnet-4");
@@ -247,9 +265,14 @@ describe("config store", () => {
         show_thinking_blocks: true,
         use_worktree: false,
         disable_1m_context: false,
+        max_output_tokens: null,
         trusted_workspaces: [],
         background_image_path: null,
         background_image_opacity: 0.3,
+        custom_font_path: null,
+        custom_font_family: null,
+        custom_ui_font_path: null,
+        custom_ui_font_family: null,
       };
 
       expect(config.model).toBeNull();
@@ -797,9 +820,14 @@ describe("config store", () => {
         show_thinking_blocks: true,
         use_worktree: false,
         disable_1m_context: false,
+        max_output_tokens: null,
         trusted_workspaces: [],
         background_image_path: null,
         background_image_opacity: 0.3,
+        custom_font_path: null,
+        custom_font_family: null,
+        custom_ui_font_path: null,
+        custom_ui_font_family: null,
       };
 
       const mockInvokeImpl = vi.mocked(invoke);
@@ -840,4 +868,607 @@ describe("config store", () => {
       expect(lastSaved.font_size).toBe(16);
     });
   });
+
+  describe("loadConfig error path", () => {
+    it("resets to default config and logs error when loadConfig fails", async () => {
+      vi.mocked(invoke).mockResolvedValue(null);
+      await configStore.updateConfig({ theme: "light" });
+
+      const consoleErrorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+      vi.mocked(invoke).mockRejectedValue(new Error("Backend unavailable"));
+
+      await configStore.loadConfig();
+
+      expect(configStore.getConfig().theme).toBe("dark");
+      expect(consoleErrorSpy).toHaveBeenCalledWith("Failed to load config:", expect.any(Error));
+      consoleErrorSpy.mockRestore();
+    });
+  });
+
+  describe("configStore sidebar methods", () => {
+    it("openSidebar sets isSidebarOpen to true", () => {
+      configStore.closeSidebar();
+      configStore.openSidebar();
+      expect(get(configStore.isSidebarOpen)).toBe(true);
+    });
+
+    it("closeSidebar sets isSidebarOpen to false", () => {
+      configStore.openSidebar();
+      configStore.closeSidebar();
+      expect(get(configStore.isSidebarOpen)).toBe(false);
+    });
+
+    it("toggleSidebar switches from false to true", () => {
+      configStore.closeSidebar();
+      configStore.toggleSidebar();
+      expect(get(configStore.isSidebarOpen)).toBe(true);
+    });
+
+    it("toggleSidebar switches from true to false", () => {
+      configStore.openSidebar();
+      configStore.toggleSidebar();
+      expect(get(configStore.isSidebarOpen)).toBe(false);
+    });
+  });
+
+  describe("configStore setTheme method", () => {
+    beforeEach(async () => {
+      vi.mocked(invoke).mockResolvedValue(null);
+    });
+
+    afterEach(() => {
+      vi.resetAllMocks();
+    });
+
+    it("setTheme updates the theme via invoke", async () => {
+      await configStore.setTheme("light");
+      expect(configStore.getConfig().theme).toBe("light");
+    });
+
+    it("setTheme with custom colors updates custom_theme_colors", async () => {
+      const colors: CustomThemeColors = {
+        bg_primary: "#001122",
+        bg_secondary: null,
+        bg_terminal: null,
+        accent_primary: null,
+        accent_secondary: null,
+        text_primary: null,
+        text_secondary: null,
+        border_color: null,
+      };
+
+      await configStore.setTheme("custom", colors);
+
+      expect(configStore.getConfig().theme).toBe("custom");
+      expect(configStore.getConfig().custom_theme_colors.bg_primary).toBe("#001122");
+    });
+  });
+
+  describe("configStore setCustomThemeColors with custom theme active", () => {
+    beforeEach(async () => {
+      vi.mocked(invoke).mockResolvedValue(null);
+      await configStore.setTheme("custom");
+    });
+
+    afterEach(() => {
+      vi.resetAllMocks();
+      clearCustomThemeColors();
+    });
+
+    it("applies custom colors to DOM when current theme is custom", async () => {
+      const colors: CustomThemeColors = {
+        bg_primary: "#aabbcc",
+        bg_secondary: null,
+        bg_terminal: null,
+        accent_primary: null,
+        accent_secondary: null,
+        text_primary: null,
+        text_secondary: null,
+        border_color: null,
+      };
+
+      await configStore.setCustomThemeColors(colors);
+
+      expect(document.documentElement.style.getPropertyValue("--bg-primary")).toBe("#aabbcc");
+    });
+  });
+
+  describe("configStore font size methods", () => {
+    beforeEach(async () => {
+      vi.mocked(invoke).mockResolvedValue(null);
+      await configStore.updateConfig({ font_size: DEFAULT_FONT_SIZE });
+      vi.resetAllMocks();
+      vi.mocked(invoke).mockResolvedValue(null);
+    });
+
+    afterEach(() => {
+      vi.resetAllMocks();
+    });
+
+    it("setFontSize updates to the given value", async () => {
+      await configStore.setFontSize(18);
+      expect(configStore.getConfig().font_size).toBe(18);
+    });
+
+    it("setFontSize clamps to minimum", async () => {
+      await configStore.setFontSize(1);
+      expect(configStore.getConfig().font_size).toBe(MIN_FONT_SIZE);
+    });
+
+    it("setFontSize clamps to maximum", async () => {
+      await configStore.setFontSize(99);
+      expect(configStore.getConfig().font_size).toBe(MAX_FONT_SIZE);
+    });
+
+    it("increaseFontSize increases font size by 2", async () => {
+      await configStore.increaseFontSize();
+      expect(configStore.getConfig().font_size).toBe(DEFAULT_FONT_SIZE + 2);
+    });
+
+    it("increaseFontSize does not exceed maximum", async () => {
+      await configStore.setFontSize(MAX_FONT_SIZE);
+      await configStore.increaseFontSize();
+      expect(configStore.getConfig().font_size).toBe(MAX_FONT_SIZE);
+    });
+
+    it("decreaseFontSize decreases font size by 2", async () => {
+      await configStore.decreaseFontSize();
+      expect(configStore.getConfig().font_size).toBe(DEFAULT_FONT_SIZE - 2);
+    });
+
+    it("decreaseFontSize does not go below minimum", async () => {
+      await configStore.setFontSize(MIN_FONT_SIZE);
+      await configStore.decreaseFontSize();
+      expect(configStore.getConfig().font_size).toBe(MIN_FONT_SIZE);
+    });
+
+    it("resetFontSize restores the default font size", async () => {
+      await configStore.setFontSize(20);
+      await configStore.resetFontSize();
+      expect(configStore.getConfig().font_size).toBe(DEFAULT_FONT_SIZE);
+    });
+  });
+
+  describe("configStore removeAutoGrantedTool", () => {
+    beforeEach(async () => {
+      vi.mocked(invoke).mockResolvedValue(null);
+      await configStore.updateConfig({ auto_granted_tools: [] });
+      vi.resetAllMocks();
+      vi.mocked(invoke).mockResolvedValue(null);
+    });
+
+    afterEach(() => {
+      vi.resetAllMocks();
+    });
+
+    it("removes an existing tool", async () => {
+      await configStore.addAutoGrantedTool("Bash");
+      await configStore.removeAutoGrantedTool("Bash");
+      expect(configStore.getConfig().auto_granted_tools).not.toContain("Bash");
+    });
+
+    it("is a no-op when the tool is not in the list", async () => {
+      await configStore.removeAutoGrantedTool("NonExistentTool");
+      expect(configStore.getConfig().auto_granted_tools).toEqual([]);
+    });
+  });
+
+  describe("configStore toggle methods", () => {
+    beforeEach(async () => {
+      vi.mocked(invoke).mockResolvedValue(null);
+      await configStore.updateConfig({ streamer_mode: false, compact_mode: false });
+      vi.resetAllMocks();
+      vi.mocked(invoke).mockResolvedValue(null);
+    });
+
+    afterEach(() => {
+      vi.resetAllMocks();
+    });
+
+    it("toggleStreamerMode flips streamer_mode from false to true", async () => {
+      await configStore.toggleStreamerMode();
+      expect(configStore.getConfig().streamer_mode).toBe(true);
+    });
+
+    it("toggleStreamerMode flips streamer_mode from true to false", async () => {
+      await configStore.updateConfig({ streamer_mode: true });
+      await configStore.toggleStreamerMode();
+      expect(configStore.getConfig().streamer_mode).toBe(false);
+    });
+
+    it("toggleCompactMode flips compact_mode from false to true", async () => {
+      await configStore.toggleCompactMode();
+      expect(configStore.getConfig().compact_mode).toBe(true);
+    });
+
+    it("toggleCompactMode flips compact_mode from true to false", async () => {
+      await configStore.updateConfig({ compact_mode: true });
+      await configStore.toggleCompactMode();
+      expect(configStore.getConfig().compact_mode).toBe(false);
+    });
+
+    it("setCompactMode enables compact mode", async () => {
+      await configStore.setCompactMode(true);
+      expect(configStore.getConfig().compact_mode).toBe(true);
+    });
+
+    it("setCompactMode disables compact mode", async () => {
+      await configStore.updateConfig({ compact_mode: true });
+      await configStore.setCompactMode(false);
+      expect(configStore.getConfig().compact_mode).toBe(false);
+    });
+  });
+
+  describe("derived stores (live subscriptions)", () => {
+    beforeEach(async () => {
+      vi.mocked(invoke).mockResolvedValue(null);
+    });
+
+    afterEach(() => {
+      vi.resetAllMocks();
+    });
+
+    it("isDarkTheme is true when theme is dark", async () => {
+      await configStore.updateConfig({ theme: "dark" });
+      expect(get(isDarkTheme)).toBe(true);
+    });
+
+    it("isDarkTheme is false when theme is not dark", async () => {
+      await configStore.updateConfig({ theme: "light" });
+      expect(get(isDarkTheme)).toBe(false);
+    });
+
+    it("isStreamerMode reflects streamer_mode config", async () => {
+      await configStore.updateConfig({ streamer_mode: true });
+      expect(get(isStreamerMode)).toBe(true);
+      await configStore.updateConfig({ streamer_mode: false });
+      expect(get(isStreamerMode)).toBe(false);
+    });
+
+    it("isCompactMode reflects compact_mode config", async () => {
+      await configStore.updateConfig({ compact_mode: true });
+      expect(get(isCompactMode)).toBe(true);
+      await configStore.updateConfig({ compact_mode: false });
+      expect(get(isCompactMode)).toBe(false);
+    });
+
+    it("shouldHidePaths is true when both streamer flags are enabled", async () => {
+      await configStore.updateConfig({ streamer_mode: true, streamer_hide_paths: true });
+      expect(get(shouldHidePaths)).toBe(true);
+    });
+
+    it("shouldHidePaths is false when streamer_mode is disabled", async () => {
+      await configStore.updateConfig({ streamer_mode: false, streamer_hide_paths: true });
+      expect(get(shouldHidePaths)).toBe(false);
+    });
+
+    it("showThinkingBlocks is true when show_thinking_blocks is enabled", async () => {
+      await configStore.updateConfig({ show_thinking_blocks: true });
+      expect(get(showThinkingBlocks)).toBe(true);
+    });
+
+    it("showThinkingBlocks is false when show_thinking_blocks is disabled", async () => {
+      await configStore.updateConfig({ show_thinking_blocks: false });
+      expect(get(showThinkingBlocks)).toBe(false);
+    });
+  });
+
+  describe("applyCustomFont", () => {
+    const readFileMock = vi.mocked(readFile);
+
+    beforeEach(() => {
+      // Remove any style element left by previous tests
+      document.getElementById("hikari-custom-font")?.remove();
+      document.documentElement.style.removeProperty("--terminal-font-family");
+      readFileMock.mockReset();
+    });
+
+    it("removes CSS variable when both path and family are null", async () => {
+      document.documentElement.style.setProperty("--terminal-font-family", "'SomeFont', monospace");
+      await applyCustomFont(null, null);
+      expect(document.documentElement.style.getPropertyValue("--terminal-font-family")).toBe("");
+    });
+
+    it("removes CSS variable when both path and family are empty strings", async () => {
+      document.documentElement.style.setProperty("--terminal-font-family", "'SomeFont', monospace");
+      await applyCustomFont("", "");
+      expect(document.documentElement.style.getPropertyValue("--terminal-font-family")).toBe("");
+      expect(document.getElementById("hikari-custom-font")).toBeNull();
+    });
+
+    it("injects @import for a CSS stylesheet URL", async () => {
+      await applyCustomFont("https://fonts.googleapis.com/css2?family=Fira+Code", "Fira Code");
+      const style = document.getElementById("hikari-custom-font");
+      expect(style).not.toBeNull();
+      expect(style?.textContent).toContain(
+        "@import url('https://fonts.googleapis.com/css2?family=Fira+Code')"
+      );
+      expect(document.documentElement.style.getPropertyValue("--terminal-font-family")).toBe(
+        "'Fira Code', monospace"
+      );
+    });
+
+    it("injects @font-face for a direct font file URL (.woff2)", async () => {
+      await applyCustomFont("https://example.com/fonts/myfont.woff2", "MyFont");
+      const style = document.getElementById("hikari-custom-font");
+      expect(style).not.toBeNull();
+      expect(style?.textContent).toContain("@font-face");
+      expect(style?.textContent).toContain("url('https://example.com/fonts/myfont.woff2')");
+      expect(style?.textContent).toContain("'MyFont'");
+      expect(document.documentElement.style.getPropertyValue("--terminal-font-family")).toBe(
+        "'MyFont', monospace"
+      );
+    });
+
+    it("injects @font-face for a direct font file URL (.ttf)", async () => {
+      await applyCustomFont("https://example.com/fonts/myfont.ttf", "MyTtfFont");
+      const style = document.getElementById("hikari-custom-font");
+      expect(style).not.toBeNull();
+      expect(style?.textContent).toContain("@font-face");
+      expect(style?.textContent).toContain("url('https://example.com/fonts/myfont.ttf')");
+      expect(style?.textContent).toContain("'MyTtfFont'");
+    });
+
+    it("uses HikariCustomFont as fallback family for direct font URLs when family is empty", async () => {
+      await applyCustomFont("https://example.com/fonts/myfont.woff2", "");
+      const style = document.getElementById("hikari-custom-font");
+      expect(style?.textContent).toContain("'HikariCustomFont'");
+    });
+
+    it("reads local file and injects @font-face with data URL", async () => {
+      const fakeData = new Uint8Array([72, 101, 108, 108, 111]); // "Hello"
+      readFileMock.mockResolvedValueOnce(fakeData);
+
+      await applyCustomFont("/home/naomi/.fonts/MyFont.ttf", "MyFont");
+
+      expect(readFileMock).toHaveBeenCalledWith("/home/naomi/.fonts/MyFont.ttf");
+      const style = document.getElementById("hikari-custom-font");
+      expect(style).not.toBeNull();
+      expect(style?.textContent).toContain("@font-face");
+      expect(style?.textContent).toContain("data:font/ttf;base64,");
+      expect(style?.textContent).toContain("'MyFont'");
+      expect(document.documentElement.style.getPropertyValue("--terminal-font-family")).toBe(
+        "'MyFont', monospace"
+      );
+    });
+
+    it("uses HikariCustomFont as fallback family for local files when family is empty", async () => {
+      const fakeData = new Uint8Array([1, 2, 3]);
+      readFileMock.mockResolvedValueOnce(fakeData);
+
+      await applyCustomFont("/home/naomi/.fonts/MyFont.woff2", "");
+
+      const style = document.getElementById("hikari-custom-font");
+      expect(style?.textContent).toContain("'HikariCustomFont'");
+      expect(style?.textContent).toContain("font/woff2");
+    });
+
+    it("sets CSS variable when only family is provided (no path)", async () => {
+      await applyCustomFont("", "SystemFont");
+      expect(document.documentElement.style.getPropertyValue("--terminal-font-family")).toBe(
+        "'SystemFont', monospace"
+      );
+      expect(document.getElementById("hikari-custom-font")).toBeNull();
+    });
+
+    it("replaces a previously injected style element", async () => {
+      await applyCustomFont("https://fonts.googleapis.com/css2?family=Fira+Code", "Fira Code");
+      expect(document.getElementById("hikari-custom-font")).not.toBeNull();
+
+      await applyCustomFont("https://fonts.googleapis.com/css2?family=Roboto+Mono", "Roboto Mono");
+      const styles = document.querySelectorAll("#hikari-custom-font");
+      expect(styles.length).toBe(1);
+      expect(styles[0].textContent).toContain("Roboto+Mono");
+    });
+
+    it("uses correct MIME type for .otf local files", async () => {
+      readFileMock.mockResolvedValueOnce(new Uint8Array([1]));
+      await applyCustomFont("/fonts/MyFont.otf", "OtfFont");
+      const style = document.getElementById("hikari-custom-font");
+      expect(style?.textContent).toContain("font/otf");
+    });
+
+    it("falls back to font/ttf MIME for unknown extension local files", async () => {
+      readFileMock.mockResolvedValueOnce(new Uint8Array([1]));
+      await applyCustomFont("/fonts/MyFont.xyz", "XyzFont");
+      const style = document.getElementById("hikari-custom-font");
+      expect(style?.textContent).toContain("font/ttf");
+    });
+  });
+
+  describe("setCustomFont", () => {
+    const readFileMock = vi.mocked(readFile);
+    const invokeMock = vi.mocked(invoke);
+
+    beforeEach(() => {
+      document.getElementById("hikari-custom-font")?.remove();
+      document.documentElement.style.removeProperty("--terminal-font-family");
+      readFileMock.mockReset();
+      invokeMock.mockResolvedValue(undefined);
+    });
+
+    it("saves config and applies the font", async () => {
+      await configStore.setCustomFont(null, null);
+      await configStore.setCustomFont(
+        "https://fonts.googleapis.com/css2?family=Fira+Code",
+        "Fira Code"
+      );
+
+      expect(invokeMock).toHaveBeenCalledWith(
+        "save_config",
+        expect.objectContaining({
+          config: expect.objectContaining({
+            custom_font_path: "https://fonts.googleapis.com/css2?family=Fira+Code",
+            custom_font_family: "Fira Code",
+          }),
+        })
+      );
+      expect(document.documentElement.style.getPropertyValue("--terminal-font-family")).toBe(
+        "'Fira Code', monospace"
+      );
+    });
+
+    it("clears font when called with nulls", async () => {
+      document.documentElement.style.setProperty("--terminal-font-family", "'SomeFont', monospace");
+      await configStore.setCustomFont(null, null);
+
+      expect(document.documentElement.style.getPropertyValue("--terminal-font-family")).toBe("");
+      expect(invokeMock).toHaveBeenCalledWith(
+        "save_config",
+        expect.objectContaining({
+          config: expect.objectContaining({
+            custom_font_path: null,
+            custom_font_family: null,
+          }),
+        })
+      );
+    });
+  });
+
+  describe("applyCustomUiFont", () => {
+    const readFileMock = vi.mocked(readFile);
+
+    beforeEach(() => {
+      document.getElementById("hikari-custom-ui-font")?.remove();
+      document.documentElement.style.removeProperty("--ui-font-family");
+      document.body.style.removeProperty("font-family");
+      readFileMock.mockReset();
+    });
+
+    it("removes CSS variable and body font-family when both path and family are null", async () => {
+      document.documentElement.style.setProperty("--ui-font-family", "'SomeFont', sans-serif");
+      document.body.style.setProperty("font-family", "'SomeFont', sans-serif");
+      await applyCustomUiFont(null, null);
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe("");
+      expect(document.body.style.getPropertyValue("font-family")).toBe("");
+    });
+
+    it("removes CSS variable and body font-family when both path and family are empty strings", async () => {
+      document.documentElement.style.setProperty("--ui-font-family", "'SomeFont', sans-serif");
+      document.body.style.setProperty("font-family", "'SomeFont', sans-serif");
+      await applyCustomUiFont("", "");
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe("");
+      expect(document.body.style.getPropertyValue("font-family")).toBe("");
+      expect(document.getElementById("hikari-custom-ui-font")).toBeNull();
+    });
+
+    it("injects @import for a CSS stylesheet URL and applies font to body", async () => {
+      await applyCustomUiFont("https://fonts.googleapis.com/css2?family=Inter", "Inter");
+      const style = document.getElementById("hikari-custom-ui-font");
+      expect(style).not.toBeNull();
+      expect(style?.textContent).toContain(
+        "@import url('https://fonts.googleapis.com/css2?family=Inter')"
+      );
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'Inter', sans-serif"
+      );
+      expect(document.body.style.getPropertyValue("font-family")).toBe('"Inter", sans-serif');
+    });
+
+    it("injects @font-face for a direct font file URL (.woff2) and applies font to body", async () => {
+      await applyCustomUiFont("https://example.com/fonts/Inter.woff2", "Inter");
+      const style = document.getElementById("hikari-custom-ui-font");
+      expect(style).not.toBeNull();
+      expect(style?.textContent).toContain("@font-face");
+      expect(style?.textContent).toContain("url('https://example.com/fonts/Inter.woff2')");
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'Inter', sans-serif"
+      );
+      expect(document.body.style.getPropertyValue("font-family")).toBe('"Inter", sans-serif');
+    });
+
+    it("uses HikariCustomUiFont as fallback family and applies it to body", async () => {
+      await applyCustomUiFont("https://example.com/fonts/Inter.woff2", "");
+      const style = document.getElementById("hikari-custom-ui-font");
+      expect(style?.textContent).toContain("'HikariCustomUiFont'");
+      expect(document.body.style.getPropertyValue("font-family")).toBe(
+        '"HikariCustomUiFont", sans-serif'
+      );
+    });
+
+    it("reads local file and embeds as data URL, applies font to body", async () => {
+      const fakeData = new Uint8Array([104, 101, 108, 108, 111]);
+      readFileMock.mockResolvedValueOnce(fakeData);
+
+      await applyCustomUiFont("/home/naomi/.fonts/Inter.ttf", "Inter");
+
+      expect(readFileMock).toHaveBeenCalledWith("/home/naomi/.fonts/Inter.ttf");
+      const style = document.getElementById("hikari-custom-ui-font");
+      expect(style?.textContent).toContain("data:font/ttf;base64,");
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'Inter', sans-serif"
+      );
+      expect(document.body.style.getPropertyValue("font-family")).toBe('"Inter", sans-serif');
+    });
+
+    it("sets CSS variable and body font-family when only family is provided (no path)", async () => {
+      await applyCustomUiFont("", "SystemUiFont");
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'SystemUiFont', sans-serif"
+      );
+      expect(document.body.style.getPropertyValue("font-family")).toBe(
+        '"SystemUiFont", sans-serif'
+      );
+    });
+
+    it("replaces a previously injected style element", async () => {
+      await applyCustomUiFont("https://fonts.googleapis.com/css2?family=Inter", "Inter");
+      expect(document.getElementById("hikari-custom-ui-font")).not.toBeNull();
+
+      await applyCustomUiFont("https://fonts.googleapis.com/css2?family=Roboto", "Roboto");
+      const styles = document.querySelectorAll("#hikari-custom-ui-font");
+      expect(styles.length).toBe(1);
+      expect(styles[0].textContent).toContain("Roboto");
+    });
+  });
+
+  describe("setCustomUiFont", () => {
+    const readFileMock = vi.mocked(readFile);
+    const invokeMock = vi.mocked(invoke);
+
+    beforeEach(() => {
+      document.getElementById("hikari-custom-ui-font")?.remove();
+      document.documentElement.style.removeProperty("--ui-font-family");
+      document.body.style.removeProperty("font-family");
+      readFileMock.mockReset();
+      invokeMock.mockResolvedValue(undefined);
+    });
+
+    it("saves config and applies the UI font", async () => {
+      await configStore.setCustomUiFont(null, null);
+      await configStore.setCustomUiFont("https://fonts.googleapis.com/css2?family=Inter", "Inter");
+
+      expect(invokeMock).toHaveBeenCalledWith(
+        "save_config",
+        expect.objectContaining({
+          config: expect.objectContaining({
+            custom_ui_font_path: "https://fonts.googleapis.com/css2?family=Inter",
+            custom_ui_font_family: "Inter",
+          }),
+        })
+      );
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'Inter', sans-serif"
+      );
+      expect(document.body.style.getPropertyValue("font-family")).toBe('"Inter", sans-serif');
+    });
+
+    it("clears UI font when called with nulls", async () => {
+      document.documentElement.style.setProperty("--ui-font-family", "'SomeFont', sans-serif");
+      document.body.style.setProperty("font-family", "'SomeFont', sans-serif");
+      await configStore.setCustomUiFont(null, null);
+
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe("");
+      expect(document.body.style.getPropertyValue("font-family")).toBe("");
+      expect(invokeMock).toHaveBeenCalledWith(
+        "save_config",
+        expect.objectContaining({
+          config: expect.objectContaining({
+            custom_ui_font_path: null,
+            custom_ui_font_family: null,
+          }),
+        })
+      );
+    });
+  });
 });