diff --git a/src/lib/sounds/achievement.test.ts b/src/lib/sounds/achievement.test.ts
new file mode 100644
index 0000000..5a023f5
--- /dev/null
+++ b/src/lib/sounds/achievement.test.ts
@@ -0,0 +1,48 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NotificationType } from "$lib/notifications/types";
+
+const mockPlay = vi.fn();
+
+vi.mock("$lib/notifications", () => ({
+  soundPlayer: {
+    play: mockPlay,
+  },
+}));
+
+describe("achievement sounds", () => {
+  beforeEach(() => {
+    mockPlay.mockReset();
+  });
+
+  describe("playAchievementSound", () => {
+    it("plays the achievement notification sound", async () => {
+      const { playAchievementSound } = await import("./achievement");
+      playAchievementSound();
+      expect(mockPlay).toHaveBeenCalledWith(NotificationType.ACHIEVEMENT);
+    });
+  });
+
+  describe("testAchievementSound", () => {
+    it("calls playAchievementSound without throwing", async () => {
+      const { testAchievementSound } = await import("./achievement");
+      expect(() => testAchievementSound()).not.toThrow();
+      expect(mockPlay).toHaveBeenCalledWith(NotificationType.ACHIEVEMENT);
+    });
+
+    it("catches errors from the sound player gracefully", async () => {
+      mockPlay.mockImplementation(() => {
+        throw new Error("Audio not available");
+      });
+      const consoleErrorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+      const { testAchievementSound } = await import("./achievement");
+      expect(() => testAchievementSound()).not.toThrow();
+      expect(consoleErrorSpy).toHaveBeenCalledWith(
+        "Error playing achievement sound:",
+        expect.any(Error)
+      );
+
+      consoleErrorSpy.mockRestore();
+    });
+  });
+});
diff --git a/src/lib/stores/character.test.ts b/src/lib/stores/character.test.ts
new file mode 100644
index 0000000..4d3d794
--- /dev/null
+++ b/src/lib/stores/character.test.ts
@@ -0,0 +1,115 @@
+/* eslint-disable max-lines-per-function -- Test suites naturally have many cases */
+import { describe, it, expect, beforeEach, vi, afterEach } from "vitest";
+import { get } from "svelte/store";
+import { characterState, characterInfo } from "./character";
+
+describe("characterState store", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    characterState.reset();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  describe("initial state", () => {
+    it("starts in idle state", () => {
+      expect(get(characterState)).toBe("idle");
+    });
+  });
+
+  describe("setState", () => {
+    it("sets the character state", () => {
+      characterState.setState("thinking");
+      expect(get(characterState)).toBe("thinking");
+    });
+
+    it("can set any valid state", () => {
+      const states = ["idle", "thinking", "typing", "coding", "searching", "mcp", "permission", "success", "error"] as const;
+      for (const state of states) {
+        characterState.setState(state);
+        expect(get(characterState)).toBe(state);
+      }
+    });
+
+    it("cancels any active temporary state timer", () => {
+      characterState.setTemporaryState("success", 5000);
+      characterState.setState("thinking");
+
+      // Advance past the temporary state duration — should stay as thinking
+      vi.advanceTimersByTime(6000);
+      expect(get(characterState)).toBe("thinking");
+    });
+  });
+
+  describe("setTemporaryState", () => {
+    it("sets the character state immediately", () => {
+      characterState.setTemporaryState("success", 2000);
+      expect(get(characterState)).toBe("success");
+    });
+
+    it("reverts to idle after the specified duration", () => {
+      characterState.setTemporaryState("success", 2000);
+      vi.advanceTimersByTime(2000);
+      expect(get(characterState)).toBe("idle");
+    });
+
+    it("uses 2000ms as the default duration", () => {
+      characterState.setTemporaryState("error");
+      vi.advanceTimersByTime(1999);
+      expect(get(characterState)).toBe("error");
+      vi.advanceTimersByTime(1);
+      expect(get(characterState)).toBe("idle");
+    });
+
+    it("cancels a previous temporary state timer when a new one is set", () => {
+      characterState.setTemporaryState("success", 5000);
+      characterState.setTemporaryState("error", 1000);
+
+      // First timer would have fired at 5000ms but was cancelled
+      vi.advanceTimersByTime(1000);
+      expect(get(characterState)).toBe("idle");
+    });
+  });
+
+  describe("reset", () => {
+    it("resets the state to idle", () => {
+      characterState.setState("thinking");
+      characterState.reset();
+      expect(get(characterState)).toBe("idle");
+    });
+
+    it("cancels any pending temporary state timer", () => {
+      characterState.setTemporaryState("success", 5000);
+      characterState.reset();
+
+      // Should now be idle and should NOT revert again after timer fires
+      expect(get(characterState)).toBe("idle");
+      vi.advanceTimersByTime(5000);
+      expect(get(characterState)).toBe("idle");
+    });
+  });
+});
+
+describe("characterInfo derived store", () => {
+  beforeEach(() => {
+    characterState.reset();
+  });
+
+  it("returns the info object for the current state", () => {
+    const info = get(characterInfo);
+    expect(info).toBeDefined();
+    expect(typeof info.label).toBe("string");
+  });
+
+  it("updates when the character state changes", () => {
+    characterState.setState("thinking");
+    const thinkingInfo = get(characterInfo);
+
+    characterState.setState("idle");
+    const idleInfo = get(characterInfo);
+
+    expect(thinkingInfo.label).not.toBe(idleInfo.label);
+  });
+});
diff --git a/src/lib/stores/costTracking.test.ts b/src/lib/stores/costTracking.test.ts
new file mode 100644
index 0000000..b573856
--- /dev/null
+++ b/src/lib/stores/costTracking.test.ts
@@ -0,0 +1,98 @@
+/* eslint-disable max-lines-per-function -- Test suites naturally have many cases */
+import { describe, it, expect } from "vitest";
+import {
+  formatCost,
+  formatAlertType,
+  getAlertMessage,
+  type AlertType,
+  type CostAlert,
+} from "./costTracking";
+
+describe("formatCost", () => {
+  it("formats amounts below $0.01 to 4 decimal places", () => {
+    expect(formatCost(0)).toBe("$0.0000");
+    expect(formatCost(0.001)).toBe("$0.0010");
+    expect(formatCost(0.0099)).toBe("$0.0099");
+  });
+
+  it("formats amounts between $0.01 and $1 to 3 decimal places", () => {
+    expect(formatCost(0.01)).toBe("$0.010");
+    expect(formatCost(0.123)).toBe("$0.123");
+    expect(formatCost(0.999)).toBe("$0.999");
+  });
+
+  it("formats amounts $1 and above to 2 decimal places", () => {
+    expect(formatCost(1)).toBe("$1.00");
+    expect(formatCost(1.5)).toBe("$1.50");
+    expect(formatCost(100.99)).toBe("$100.99");
+  });
+});
+
+describe("formatAlertType", () => {
+  it("formats Daily as Today", () => {
+    expect(formatAlertType("Daily")).toBe("Today");
+  });
+
+  it("formats Weekly as This Week", () => {
+    expect(formatAlertType("Weekly")).toBe("This Week");
+  });
+
+  it("formats Monthly as This Month", () => {
+    expect(formatAlertType("Monthly")).toBe("This Month");
+  });
+
+  it("handles all AlertType values", () => {
+    const types: AlertType[] = ["Daily", "Weekly", "Monthly"];
+    const results = types.map(formatAlertType);
+    expect(results).toEqual(["Today", "This Week", "This Month"]);
+  });
+});
+
+describe("getAlertMessage", () => {
+  it("generates a message for a Daily alert", () => {
+    const alert: CostAlert = {
+      alert_type: "Daily",
+      threshold: 1.0,
+      current_cost: 1.5,
+    };
+    const message = getAlertMessage(alert);
+    expect(message).toContain("Today");
+    expect(message).toContain("$1.50");
+    expect(message).toContain("$1.00");
+  });
+
+  it("generates a message for a Weekly alert", () => {
+    const alert: CostAlert = {
+      alert_type: "Weekly",
+      threshold: 5.0,
+      current_cost: 6.0,
+    };
+    const message = getAlertMessage(alert);
+    expect(message).toContain("This Week");
+    expect(message).toContain("$6.00");
+    expect(message).toContain("$5.00");
+  });
+
+  it("generates a message for a Monthly alert", () => {
+    const alert: CostAlert = {
+      alert_type: "Monthly",
+      threshold: 20.0,
+      current_cost: 25.0,
+    };
+    const message = getAlertMessage(alert);
+    expect(message).toContain("This Month");
+    expect(message).toContain("$25.00");
+    expect(message).toContain("$20.00");
+  });
+
+  it("includes threshold and current cost in the message", () => {
+    const alert: CostAlert = {
+      alert_type: "Daily",
+      threshold: 0.005,
+      current_cost: 0.007,
+    };
+    const message = getAlertMessage(alert);
+    expect(message).toContain("$0.0070");
+    expect(message).toContain("$0.0050");
+  });
+});
diff --git a/src/lib/stores/historyRestore.test.ts b/src/lib/stores/historyRestore.test.ts
new file mode 100644
index 0000000..e298a64
--- /dev/null
+++ b/src/lib/stores/historyRestore.test.ts
@@ -0,0 +1,72 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import {
+  setShouldRestoreHistory,
+  setSavedHistory,
+  getShouldRestoreHistory,
+  getSavedHistory,
+  clearHistoryRestore,
+} from "./historyRestore";
+
+describe("historyRestore module", () => {
+  beforeEach(() => {
+    clearHistoryRestore();
+  });
+
+  describe("initial state", () => {
+    it("shouldRestoreHistory is false by default", () => {
+      expect(getShouldRestoreHistory()).toBe(false);
+    });
+
+    it("savedHistory is null by default", () => {
+      expect(getSavedHistory()).toBeNull();
+    });
+  });
+
+  describe("setShouldRestoreHistory", () => {
+    it("sets shouldRestoreHistory to true", () => {
+      setShouldRestoreHistory(true);
+      expect(getShouldRestoreHistory()).toBe(true);
+    });
+
+    it("sets shouldRestoreHistory to false", () => {
+      setShouldRestoreHistory(true);
+      setShouldRestoreHistory(false);
+      expect(getShouldRestoreHistory()).toBe(false);
+    });
+  });
+
+  describe("setSavedHistory", () => {
+    it("sets the saved history string", () => {
+      setSavedHistory("some history content");
+      expect(getSavedHistory()).toBe("some history content");
+    });
+
+    it("sets the saved history to null", () => {
+      setSavedHistory("some history content");
+      setSavedHistory(null);
+      expect(getSavedHistory()).toBeNull();
+    });
+  });
+
+  describe("clearHistoryRestore", () => {
+    it("resets shouldRestoreHistory to false", () => {
+      setShouldRestoreHistory(true);
+      clearHistoryRestore();
+      expect(getShouldRestoreHistory()).toBe(false);
+    });
+
+    it("resets savedHistory to null", () => {
+      setSavedHistory("some content");
+      clearHistoryRestore();
+      expect(getSavedHistory()).toBeNull();
+    });
+
+    it("clears both values at once", () => {
+      setShouldRestoreHistory(true);
+      setSavedHistory("history");
+      clearHistoryRestore();
+      expect(getShouldRestoreHistory()).toBe(false);
+      expect(getSavedHistory()).toBeNull();
+    });
+  });
+});
diff --git a/src/lib/stores/messageMode.test.ts b/src/lib/stores/messageMode.test.ts
new file mode 100644
index 0000000..7b3a703
--- /dev/null
+++ b/src/lib/stores/messageMode.test.ts
@@ -0,0 +1,56 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { get } from "svelte/store";
+import { messageMode, getCurrentMode } from "./messageMode";
+
+describe("messageMode store", () => {
+  beforeEach(() => {
+    messageMode.reset();
+  });
+
+  describe("initial state", () => {
+    it("defaults to chat mode", () => {
+      expect(get(messageMode)).toBe("chat");
+    });
+  });
+
+  describe("set", () => {
+    it("sets the mode to the given value", () => {
+      messageMode.set("plan");
+      expect(get(messageMode)).toBe("plan");
+    });
+
+    it("can set any arbitrary mode string", () => {
+      messageMode.set("auto");
+      expect(get(messageMode)).toBe("auto");
+    });
+  });
+
+  describe("reset", () => {
+    it("resets mode back to chat", () => {
+      messageMode.set("plan");
+      messageMode.reset();
+      expect(get(messageMode)).toBe("chat");
+    });
+  });
+});
+
+describe("getCurrentMode", () => {
+  beforeEach(() => {
+    messageMode.reset();
+  });
+
+  it("returns chat when in default state", () => {
+    expect(getCurrentMode()).toBe("chat");
+  });
+
+  it("returns the currently set mode", () => {
+    messageMode.set("plan");
+    expect(getCurrentMode()).toBe("plan");
+  });
+
+  it("returns chat after a reset", () => {
+    messageMode.set("auto");
+    messageMode.reset();
+    expect(getCurrentMode()).toBe("chat");
+  });
+});
diff --git a/src/lib/stores/notifications.test.ts b/src/lib/stores/notifications.test.ts
new file mode 100644
index 0000000..78132dd
--- /dev/null
+++ b/src/lib/stores/notifications.test.ts
@@ -0,0 +1,105 @@
+/* eslint-disable @typescript-eslint/init-declarations -- Variables reassigned in beforeEach */
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { writable } from "svelte/store";
+
+const mockSetEnabled = vi.fn();
+const mockSetGlobalVolume = vi.fn();
+
+vi.mock("$lib/notifications", () => ({
+  soundPlayer: {
+    setEnabled: mockSetEnabled,
+    setGlobalVolume: mockSetGlobalVolume,
+  },
+}));
+
+// We need to control the config store's emitted values
+const configWritable = writable({
+  notifications_enabled: true,
+  notification_volume: 0.7,
+});
+
+vi.mock("./config", () => ({
+  configStore: {
+    config: { subscribe: configWritable.subscribe },
+  },
+}));
+
+describe("notifications sync store", () => {
+  beforeEach(async () => {
+    vi.resetModules();
+    mockSetEnabled.mockReset();
+    mockSetGlobalVolume.mockReset();
+    configWritable.set({ notifications_enabled: true, notification_volume: 0.7 });
+  });
+
+  afterEach(async () => {
+    // Re-import to clean up any lingering subscriptions
+    const { cleanupNotificationSync } = await import("./notifications");
+    cleanupNotificationSync();
+  });
+
+  describe("initNotificationSync", () => {
+    it("syncs soundPlayer enabled state from config on init", async () => {
+      const { initNotificationSync } = await import("./notifications");
+      initNotificationSync();
+      expect(mockSetEnabled).toHaveBeenCalledWith(true);
+    });
+
+    it("syncs soundPlayer volume from config on init", async () => {
+      const { initNotificationSync } = await import("./notifications");
+      initNotificationSync();
+      expect(mockSetGlobalVolume).toHaveBeenCalledWith(0.7);
+    });
+
+    it("updates soundPlayer when config changes", async () => {
+      const { initNotificationSync } = await import("./notifications");
+      initNotificationSync();
+
+      mockSetEnabled.mockReset();
+      mockSetGlobalVolume.mockReset();
+
+      configWritable.set({ notifications_enabled: false, notification_volume: 0.3 });
+
+      expect(mockSetEnabled).toHaveBeenCalledWith(false);
+      expect(mockSetGlobalVolume).toHaveBeenCalledWith(0.3);
+    });
+
+    it("does not register a duplicate subscription when called twice", async () => {
+      const { initNotificationSync } = await import("./notifications");
+      initNotificationSync();
+      initNotificationSync();
+
+      // Both calls should only produce one subscription (one initial sync)
+      expect(mockSetEnabled).toHaveBeenCalledTimes(1);
+    });
+  });
+
+  describe("cleanupNotificationSync", () => {
+    it("stops reacting to config changes after cleanup", async () => {
+      const { initNotificationSync, cleanupNotificationSync } = await import("./notifications");
+      initNotificationSync();
+      cleanupNotificationSync();
+
+      mockSetEnabled.mockReset();
+      configWritable.set({ notifications_enabled: false, notification_volume: 0.5 });
+
+      expect(mockSetEnabled).not.toHaveBeenCalled();
+    });
+
+    it("is safe to call when not initialised", async () => {
+      const { cleanupNotificationSync } = await import("./notifications");
+      expect(() => cleanupNotificationSync()).not.toThrow();
+    });
+
+    it("allows re-initialisation after cleanup", async () => {
+      const { initNotificationSync, cleanupNotificationSync } = await import("./notifications");
+      initNotificationSync();
+      cleanupNotificationSync();
+
+      mockSetEnabled.mockReset();
+      initNotificationSync();
+
+      expect(mockSetEnabled).toHaveBeenCalledTimes(1);
+    });
+  });
+});
diff --git a/src/lib/stores/search.test.ts b/src/lib/stores/search.test.ts
new file mode 100644
index 0000000..f46d3aa
--- /dev/null
+++ b/src/lib/stores/search.test.ts
@@ -0,0 +1,188 @@
+/* eslint-disable max-lines-per-function -- Test suites naturally have many cases */
+import { describe, it, expect, beforeEach } from "vitest";
+import { get } from "svelte/store";
+import { searchState, isSearchActive, searchQuery } from "./search";
+
+describe("searchState store", () => {
+  beforeEach(() => {
+    searchState.clear();
+  });
+
+  describe("initial state", () => {
+    it("starts with empty query", () => {
+      const state = get(searchState);
+      expect(state.query).toBe("");
+    });
+
+    it("starts inactive", () => {
+      const state = get(searchState);
+      expect(state.isActive).toBe(false);
+    });
+
+    it("starts with zero match count", () => {
+      const state = get(searchState);
+      expect(state.matchCount).toBe(0);
+    });
+
+    it("starts with zero current match index", () => {
+      const state = get(searchState);
+      expect(state.currentMatchIndex).toBe(0);
+    });
+  });
+
+  describe("setQuery", () => {
+    it("sets the query string", () => {
+      searchState.setQuery("hello");
+      expect(get(searchState).query).toBe("hello");
+    });
+
+    it("activates the store when query is non-empty", () => {
+      searchState.setQuery("hello");
+      expect(get(searchState).isActive).toBe(true);
+    });
+
+    it("deactivates the store when query is empty", () => {
+      searchState.setQuery("hello");
+      searchState.setQuery("");
+      expect(get(searchState).isActive).toBe(false);
+    });
+
+    it("resets currentMatchIndex to 0 on each query change", () => {
+      searchState.setQuery("hello");
+      searchState.setMatchCount(5);
+      searchState.nextMatch();
+      searchState.nextMatch();
+      searchState.setQuery("world");
+      expect(get(searchState).currentMatchIndex).toBe(0);
+    });
+  });
+
+  describe("setMatchCount", () => {
+    it("updates the match count", () => {
+      searchState.setMatchCount(7);
+      expect(get(searchState).matchCount).toBe(7);
+    });
+
+    it("does not reset currentMatchIndex", () => {
+      searchState.setQuery("test");
+      searchState.setMatchCount(5);
+      searchState.nextMatch();
+      searchState.setMatchCount(10);
+      expect(get(searchState).currentMatchIndex).toBe(1);
+    });
+  });
+
+  describe("nextMatch", () => {
+    it("advances to the next match index", () => {
+      searchState.setMatchCount(5);
+      searchState.nextMatch();
+      expect(get(searchState).currentMatchIndex).toBe(1);
+    });
+
+    it("wraps around to 0 after the last match", () => {
+      searchState.setMatchCount(3);
+      searchState.nextMatch();
+      searchState.nextMatch();
+      searchState.nextMatch();
+      expect(get(searchState).currentMatchIndex).toBe(0);
+    });
+
+    it("stays at 0 when match count is 0", () => {
+      searchState.setMatchCount(0);
+      searchState.nextMatch();
+      expect(get(searchState).currentMatchIndex).toBe(0);
+    });
+  });
+
+  describe("previousMatch", () => {
+    it("goes to the previous match index", () => {
+      searchState.setMatchCount(5);
+      searchState.nextMatch();
+      searchState.nextMatch();
+      searchState.previousMatch();
+      expect(get(searchState).currentMatchIndex).toBe(1);
+    });
+
+    it("wraps around to last match when at index 0", () => {
+      searchState.setMatchCount(5);
+      searchState.previousMatch();
+      expect(get(searchState).currentMatchIndex).toBe(4);
+    });
+
+    it("stays at 0 when match count is 0", () => {
+      searchState.setMatchCount(0);
+      searchState.previousMatch();
+      expect(get(searchState).currentMatchIndex).toBe(0);
+    });
+  });
+
+  describe("clear", () => {
+    it("resets query to empty string", () => {
+      searchState.setQuery("hello");
+      searchState.clear();
+      expect(get(searchState).query).toBe("");
+    });
+
+    it("resets isActive to false", () => {
+      searchState.setQuery("hello");
+      searchState.clear();
+      expect(get(searchState).isActive).toBe(false);
+    });
+
+    it("resets matchCount to 0", () => {
+      searchState.setMatchCount(10);
+      searchState.clear();
+      expect(get(searchState).matchCount).toBe(0);
+    });
+
+    it("resets currentMatchIndex to 0", () => {
+      searchState.setMatchCount(5);
+      searchState.nextMatch();
+      searchState.nextMatch();
+      searchState.clear();
+      expect(get(searchState).currentMatchIndex).toBe(0);
+    });
+  });
+});
+
+describe("isSearchActive derived store", () => {
+  beforeEach(() => {
+    searchState.clear();
+  });
+
+  it("is false initially", () => {
+    expect(get(isSearchActive)).toBe(false);
+  });
+
+  it("is true when query is set", () => {
+    searchState.setQuery("test");
+    expect(get(isSearchActive)).toBe(true);
+  });
+
+  it("is false after clearing", () => {
+    searchState.setQuery("test");
+    searchState.clear();
+    expect(get(isSearchActive)).toBe(false);
+  });
+});
+
+describe("searchQuery derived store", () => {
+  beforeEach(() => {
+    searchState.clear();
+  });
+
+  it("is empty string initially", () => {
+    expect(get(searchQuery)).toBe("");
+  });
+
+  it("reflects the current query", () => {
+    searchState.setQuery("my search");
+    expect(get(searchQuery)).toBe("my search");
+  });
+
+  it("is empty after clearing", () => {
+    searchState.setQuery("test");
+    searchState.clear();
+    expect(get(searchQuery)).toBe("");
+  });
+});
diff --git a/src/lib/stores/stats.test.ts b/src/lib/stores/stats.test.ts
index 37259b7..c1da40b 100644
--- a/src/lib/stores/stats.test.ts
+++ b/src/lib/stores/stats.test.ts
@@ -9,8 +9,12 @@ import {
   estimateMessageCost,
   formatTokenCount,
   MODEL_PRICING,
+  checkBudget,
+  getBudgetStatusMessage,
+  getRemainingTokenBudget,
+  getRemainingCostBudget,
 } 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 {
@@ -600,4 +604,201 @@ 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);
+    });
+  });
 });
diff --git a/src/lib/stores/todos.test.ts b/src/lib/stores/todos.test.ts
new file mode 100644
index 0000000..0c65886
--- /dev/null
+++ b/src/lib/stores/todos.test.ts
@@ -0,0 +1,93 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { get } from "svelte/store";
+import { emitMockEvent } from "../../../vitest.setup";
+import { todos, initializeTodoListener, cleanupTodoListener } from "./todos";
+import type { TodoItem } from "./todos";
+
+describe("todos store", () => {
+  beforeEach(() => {
+    cleanupTodoListener();
+    todos.clear();
+  });
+
+  describe("initial state", () => {
+    it("starts with an empty list", () => {
+      expect(get(todos)).toEqual([]);
+    });
+  });
+
+  describe("set and clear", () => {
+    it("can set todos directly", () => {
+      const items: TodoItem[] = [
+        { content: "Task 1", status: "pending", activeForm: "Doing task 1" },
+        { content: "Task 2", status: "in_progress", activeForm: "Doing task 2" },
+      ];
+      todos.set(items);
+      expect(get(todos)).toEqual(items);
+    });
+
+    it("clear resets to empty array", () => {
+      todos.set([{ content: "Task", status: "completed", activeForm: "Doing task" }]);
+      todos.clear();
+      expect(get(todos)).toEqual([]);
+    });
+  });
+
+  describe("update", () => {
+    it("can update todos with a callback", () => {
+      const initial: TodoItem[] = [
+        { content: "Task 1", status: "pending", activeForm: "Doing task 1" },
+      ];
+      todos.set(initial);
+      todos.update((current) => [
+        ...current,
+        { content: "Task 2", status: "completed", activeForm: "Doing task 2" },
+      ]);
+      expect(get(todos)).toHaveLength(2);
+    });
+  });
+
+  describe("initializeTodoListener", () => {
+    it("listens for claude:todo-update events", async () => {
+      await initializeTodoListener();
+
+      const newTodos: TodoItem[] = [
+        { content: "Backend task", status: "in_progress", activeForm: "Running backend task" },
+      ];
+      emitMockEvent("claude:todo-update", { todos: newTodos });
+
+      expect(get(todos)).toEqual(newTodos);
+    });
+
+    it("does not register a duplicate listener when called twice", async () => {
+      await initializeTodoListener();
+      await initializeTodoListener();
+
+      const newTodos: TodoItem[] = [
+        { content: "Task", status: "pending", activeForm: "Doing task" },
+      ];
+      emitMockEvent("claude:todo-update", { todos: newTodos });
+
+      // Should only have been set once (not doubled)
+      expect(get(todos)).toEqual(newTodos);
+    });
+  });
+
+  describe("cleanupTodoListener", () => {
+    it("stops listening for events after cleanup", async () => {
+      await initializeTodoListener();
+      cleanupTodoListener();
+
+      emitMockEvent("claude:todo-update", {
+        todos: [{ content: "Task", status: "pending", activeForm: "Doing task" }],
+      });
+
+      // Should not have been updated since we cleaned up
+      expect(get(todos)).toEqual([]);
+    });
+
+    it("is safe to call when not initialised", () => {
+      expect(() => cleanupTodoListener()).not.toThrow();
+    });
+  });
+});