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/stats.test.ts

@@ -1,5 +1,7 @@
-import { describe, it, expect, beforeEach, vi } from "vitest";
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
 import { get } from "svelte/store";
+import { listen } from "@tauri-apps/api/event";
+import { invoke } from "@tauri-apps/api/core";
 import {
   stats,
   formattedStats,
@@ -9,8 +11,13 @@ import {
   estimateMessageCost,
   formatTokenCount,
   MODEL_PRICING,
+  checkBudget,
+  getBudgetStatusMessage,
+  getRemainingTokenBudget,
+  getRemainingCostBudget,
+  initStatsListener,
 } from "./stats";
-import type { UsageStats, ToolTokenStats } from "./stats";
+import type { UsageStats, ToolTokenStats, BudgetStatus } from "./stats";
 
 // Helper function to create ToolTokenStats for tests
 function toolStats(callCount: number, inputTokens = 0, outputTokens = 0): ToolTokenStats {
@@ -30,6 +37,12 @@ vi.mock("@tauri-apps/api/core", () => ({
   invoke: vi.fn(),
 }));
 
+vi.mock("./costTracking", () => ({
+  costTrackingStore: {
+    refresh: vi.fn().mockResolvedValue([]),
+  },
+}));
+
 describe("stats store", () => {
   beforeEach(() => {
     // Reset stats to default before each test
@@ -600,4 +613,282 @@ describe("stats store", () => {
       expect(MODEL_PRICING["claude-3-haiku-20240307"]).toEqual({ input: 0.25, output: 1.25 });
     });
   });
+
+  describe("checkBudget", () => {
+    const baseStats: UsageStats = {
+      total_input_tokens: 0,
+      total_output_tokens: 0,
+      total_cost_usd: 0,
+      session_input_tokens: 500,
+      session_output_tokens: 500,
+      session_cost_usd: 0.5,
+      model: null,
+      messages_exchanged: 0,
+      session_messages_exchanged: 0,
+      code_blocks_generated: 0,
+      session_code_blocks_generated: 0,
+      files_edited: 0,
+      session_files_edited: 0,
+      files_created: 0,
+      session_files_created: 0,
+      tools_usage: {},
+      session_tools_usage: {},
+      session_duration_seconds: 0,
+      context_tokens_used: 0,
+      context_window_limit: 200000,
+      context_utilisation_percent: 0,
+      potential_cache_hits: 0,
+      potential_cache_savings_tokens: 0,
+    };
+
+    it("returns ok when budget is disabled", () => {
+      const result = checkBudget(baseStats, false, 100, 1.0, 0.8);
+      expect(result).toEqual({ type: "ok" });
+    });
+
+    it("returns ok when under all budgets", () => {
+      const result = checkBudget(baseStats, true, 10000, 10.0, 0.8);
+      expect(result).toEqual({ type: "ok" });
+    });
+
+    it("returns exceeded when token budget is reached", () => {
+      const result = checkBudget(baseStats, true, 1000, null, 0.8);
+      expect(result).toEqual({ type: "exceeded", budget_type: "token" });
+    });
+
+    it("returns warning when token usage is above threshold", () => {
+      // session tokens = 1000, budget = 1100, threshold = 0.8 → 1000/1100 ≈ 0.909 > 0.8
+      const result = checkBudget(baseStats, true, 1100, null, 0.8);
+      expect(result.type).toBe("warning");
+      if (result.type === "warning") {
+        expect(result.budget_type).toBe("token");
+        expect(result.percent_used).toBeGreaterThan(80);
+      }
+    });
+
+    it("returns exceeded when cost budget is reached", () => {
+      const result = checkBudget(baseStats, true, null, 0.5, 0.8);
+      expect(result).toEqual({ type: "exceeded", budget_type: "cost" });
+    });
+
+    it("returns warning when cost usage is above threshold", () => {
+      // session cost = 0.5, budget = 0.55, threshold = 0.8 → 0.5/0.55 ≈ 0.909 > 0.8
+      const result = checkBudget(baseStats, true, null, 0.55, 0.8);
+      expect(result.type).toBe("warning");
+      if (result.type === "warning") {
+        expect(result.budget_type).toBe("cost");
+      }
+    });
+
+    it("checks token budget before cost budget", () => {
+      // Both budgets exceeded, but token should be reported first
+      const result = checkBudget(baseStats, true, 500, 0.1, 0.8);
+      expect(result).toEqual({ type: "exceeded", budget_type: "token" });
+    });
+
+    it("returns ok when no budgets are set", () => {
+      const result = checkBudget(baseStats, true, null, null, 0.8);
+      expect(result).toEqual({ type: "ok" });
+    });
+  });
+
+  describe("getBudgetStatusMessage", () => {
+    it("returns null for ok status", () => {
+      const status: BudgetStatus = { type: "ok" };
+      expect(getBudgetStatusMessage(status)).toBeNull();
+    });
+
+    it("returns exceeded message for token budget", () => {
+      const status: BudgetStatus = { type: "exceeded", budget_type: "token" };
+      const message = getBudgetStatusMessage(status);
+      expect(message).toContain("token");
+      expect(message).toContain("exceeded");
+    });
+
+    it("returns exceeded message for cost budget", () => {
+      const status: BudgetStatus = { type: "exceeded", budget_type: "cost" };
+      const message = getBudgetStatusMessage(status);
+      expect(message).toContain("cost");
+      expect(message).toContain("exceeded");
+    });
+
+    it("returns warning message with percentage for token budget", () => {
+      const status: BudgetStatus = { type: "warning", budget_type: "token", percent_used: 85.5 };
+      const message = getBudgetStatusMessage(status);
+      expect(message).toContain("token");
+      expect(message).toContain("86%");
+    });
+
+    it("returns warning message with percentage for cost budget", () => {
+      const status: BudgetStatus = { type: "warning", budget_type: "cost", percent_used: 90 };
+      const message = getBudgetStatusMessage(status);
+      expect(message).toContain("cost");
+      expect(message).toContain("90%");
+    });
+  });
+
+  describe("getRemainingTokenBudget", () => {
+    const baseStats: UsageStats = {
+      total_input_tokens: 0,
+      total_output_tokens: 0,
+      total_cost_usd: 0,
+      session_input_tokens: 300,
+      session_output_tokens: 200,
+      session_cost_usd: 0,
+      model: null,
+      messages_exchanged: 0,
+      session_messages_exchanged: 0,
+      code_blocks_generated: 0,
+      session_code_blocks_generated: 0,
+      files_edited: 0,
+      session_files_edited: 0,
+      files_created: 0,
+      session_files_created: 0,
+      tools_usage: {},
+      session_tools_usage: {},
+      session_duration_seconds: 0,
+      context_tokens_used: 0,
+      context_window_limit: 200000,
+      context_utilisation_percent: 0,
+      potential_cache_hits: 0,
+      potential_cache_savings_tokens: 0,
+    };
+
+    it("returns null when no token budget is set", () => {
+      expect(getRemainingTokenBudget(baseStats, null)).toBeNull();
+    });
+
+    it("returns the remaining tokens when under budget", () => {
+      // session tokens = 500, budget = 1000 → remaining = 500
+      expect(getRemainingTokenBudget(baseStats, 1000)).toBe(500);
+    });
+
+    it("returns 0 when at or over budget", () => {
+      expect(getRemainingTokenBudget(baseStats, 500)).toBe(0);
+      expect(getRemainingTokenBudget(baseStats, 400)).toBe(0);
+    });
+  });
+
+  describe("getRemainingCostBudget", () => {
+    const baseStats: UsageStats = {
+      total_input_tokens: 0,
+      total_output_tokens: 0,
+      total_cost_usd: 0,
+      session_input_tokens: 0,
+      session_output_tokens: 0,
+      session_cost_usd: 0.3,
+      model: null,
+      messages_exchanged: 0,
+      session_messages_exchanged: 0,
+      code_blocks_generated: 0,
+      session_code_blocks_generated: 0,
+      files_edited: 0,
+      session_files_edited: 0,
+      files_created: 0,
+      session_files_created: 0,
+      tools_usage: {},
+      session_tools_usage: {},
+      session_duration_seconds: 0,
+      context_tokens_used: 0,
+      context_window_limit: 200000,
+      context_utilisation_percent: 0,
+      potential_cache_hits: 0,
+      potential_cache_savings_tokens: 0,
+    };
+
+    it("returns null when no cost budget is set", () => {
+      expect(getRemainingCostBudget(baseStats, null)).toBeNull();
+    });
+
+    it("returns the remaining cost when under budget", () => {
+      // session cost = 0.3, budget = 1.0 → remaining = 0.7
+      expect(getRemainingCostBudget(baseStats, 1.0)).toBeCloseTo(0.7, 5);
+    });
+
+    it("returns 0 when at or over budget", () => {
+      expect(getRemainingCostBudget(baseStats, 0.3)).toBe(0);
+      expect(getRemainingCostBudget(baseStats, 0.2)).toBe(0);
+    });
+  });
+
+  describe("initStatsListener", () => {
+    const emptyStats: UsageStats = {
+      total_input_tokens: 0,
+      total_output_tokens: 0,
+      total_cost_usd: 0,
+      session_input_tokens: 0,
+      session_output_tokens: 0,
+      session_cost_usd: 0,
+      model: null,
+      messages_exchanged: 0,
+      session_messages_exchanged: 0,
+      code_blocks_generated: 0,
+      session_code_blocks_generated: 0,
+      files_edited: 0,
+      session_files_edited: 0,
+      files_created: 0,
+      session_files_created: 0,
+      tools_usage: {},
+      session_tools_usage: {},
+      session_duration_seconds: 0,
+      context_tokens_used: 0,
+      context_window_limit: 200000,
+      context_utilisation_percent: 0,
+      potential_cache_hits: 0,
+      potential_cache_savings_tokens: 0,
+    };
+
+    afterEach(() => {
+      vi.resetAllMocks();
+    });
+
+    it("registers a listener for the claude:stats event", async () => {
+      vi.mocked(listen).mockResolvedValue(vi.fn());
+      vi.mocked(invoke).mockResolvedValue(emptyStats);
+
+      await initStatsListener();
+
+      expect(listen).toHaveBeenCalledWith("claude:stats", expect.any(Function));
+    });
+
+    it("updates the stats store when the listener callback fires", async () => {
+      let capturedCallback: ((event: unknown) => void) | undefined;
+      vi.mocked(listen).mockImplementation(async (_event, callback) => {
+        capturedCallback = callback as (event: unknown) => void;
+        return () => {};
+      });
+      vi.mocked(invoke).mockResolvedValue(emptyStats);
+
+      await initStatsListener();
+
+      const newStats = { ...emptyStats, total_input_tokens: 9999 };
+      capturedCallback!({ payload: { stats: newStats } });
+
+      expect(get(stats).total_input_tokens).toBe(9999);
+    });
+
+    it("loads persisted stats from the backend on initialisation", async () => {
+      const persistedStats = { ...emptyStats, total_input_tokens: 5000 };
+      vi.mocked(listen).mockResolvedValue(vi.fn());
+      vi.mocked(invoke).mockResolvedValue(persistedStats);
+
+      await initStatsListener();
+
+      expect(invoke).toHaveBeenCalledWith("get_persisted_stats");
+      expect(get(stats).total_input_tokens).toBe(5000);
+    });
+
+    it("handles a failed invoke gracefully and logs the error", async () => {
+      const error = new Error("Failed to get stats");
+      vi.mocked(listen).mockResolvedValue(vi.fn());
+      vi.mocked(invoke).mockRejectedValue(error);
+
+      const consoleErrorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+      await initStatsListener();
+
+      expect(consoleErrorSpy).toHaveBeenCalledWith("Failed to load initial stats:", error);
+      consoleErrorSpy.mockRestore();
+    });
+  });
 });