diff --git a/src/agent/context-window/guard.test.ts b/src/agent/context-window/guard.test.ts
new file mode 100644
index 00000000..7bc7ed42
--- /dev/null
+++ b/src/agent/context-window/guard.test.ts
@@ -0,0 +1,259 @@
+import { describe, it, expect } from "vitest";
+import {
+  CONTEXT_WINDOW_HARD_MIN_TOKENS,
+  CONTEXT_WINDOW_WARN_BELOW_TOKENS,
+  DEFAULT_CONTEXT_TOKENS,
+  resolveContextWindowInfo,
+  evaluateContextWindowGuard,
+  checkContextWindow,
+} from "./guard.js";
+
+describe("guard", () => {
+  describe("constants", () => {
+    it("should have correct hard minimum tokens", () => {
+      expect(CONTEXT_WINDOW_HARD_MIN_TOKENS).toBe(16_000);
+    });
+
+    it("should have correct warning threshold tokens", () => {
+      expect(CONTEXT_WINDOW_WARN_BELOW_TOKENS).toBe(32_000);
+    });
+
+    it("should have correct default context tokens", () => {
+      expect(DEFAULT_CONTEXT_TOKENS).toBe(200_000);
+    });
+  });
+
+  describe("resolveContextWindowInfo", () => {
+    it("should prioritize model context window", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: 100_000,
+        configContextTokens: 50_000,
+        defaultTokens: 200_000,
+      });
+
+      expect(result.tokens).toBe(100_000);
+      expect(result.source).toBe("model");
+    });
+
+    it("should fall back to config when model is undefined", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: undefined,
+        configContextTokens: 50_000,
+        defaultTokens: 200_000,
+      });
+
+      expect(result.tokens).toBe(50_000);
+      expect(result.source).toBe("config");
+    });
+
+    it("should fall back to default when both model and config are undefined", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: undefined,
+        configContextTokens: undefined,
+        defaultTokens: 150_000,
+      });
+
+      expect(result.tokens).toBe(150_000);
+      expect(result.source).toBe("default");
+    });
+
+    it("should use DEFAULT_CONTEXT_TOKENS when no default provided", () => {
+      const result = resolveContextWindowInfo({});
+
+      expect(result.tokens).toBe(DEFAULT_CONTEXT_TOKENS);
+      expect(result.source).toBe("default");
+    });
+
+    it("should ignore non-positive model values", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: 0,
+        configContextTokens: 50_000,
+      });
+
+      expect(result.tokens).toBe(50_000);
+      expect(result.source).toBe("config");
+    });
+
+    it("should ignore negative model values", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: -1000,
+        configContextTokens: 50_000,
+      });
+
+      expect(result.tokens).toBe(50_000);
+      expect(result.source).toBe("config");
+    });
+
+    it("should ignore NaN values", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: NaN,
+        configContextTokens: NaN,
+        defaultTokens: 100_000,
+      });
+
+      expect(result.tokens).toBe(100_000);
+      expect(result.source).toBe("default");
+    });
+
+    it("should ignore Infinity values", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: Infinity,
+        configContextTokens: 50_000,
+      });
+
+      expect(result.tokens).toBe(50_000);
+      expect(result.source).toBe("config");
+    });
+
+    it("should floor decimal values", () => {
+      const result = resolveContextWindowInfo({
+        modelContextWindow: 100_000.9,
+      });
+
+      expect(result.tokens).toBe(100_000);
+    });
+  });
+
+  describe("evaluateContextWindowGuard", () => {
+    it("should not warn or block when tokens are high enough", () => {
+      const result = evaluateContextWindowGuard({
+        info: { tokens: 100_000, source: "model" },
+      });
+
+      expect(result.shouldWarn).toBe(false);
+      expect(result.shouldBlock).toBe(false);
+      expect(result.tokens).toBe(100_000);
+      expect(result.source).toBe("model");
+    });
+
+    it("should warn but not block when tokens are between thresholds", () => {
+      const result = evaluateContextWindowGuard({
+        info: { tokens: 20_000, source: "config" },
+      });
+
+      expect(result.shouldWarn).toBe(true);
+      expect(result.shouldBlock).toBe(false);
+    });
+
+    it("should both warn and block when tokens are below hard minimum", () => {
+      const result = evaluateContextWindowGuard({
+        info: { tokens: 10_000, source: "default" },
+      });
+
+      expect(result.shouldWarn).toBe(true);
+      expect(result.shouldBlock).toBe(true);
+    });
+
+    it("should use custom thresholds", () => {
+      const result = evaluateContextWindowGuard({
+        info: { tokens: 5_000, source: "model" },
+        warnBelowTokens: 10_000,
+        hardMinTokens: 3_000,
+      });
+
+      expect(result.shouldWarn).toBe(true);
+      expect(result.shouldBlock).toBe(false);
+    });
+
+    it("should block with custom hard minimum", () => {
+      const result = evaluateContextWindowGuard({
+        info: { tokens: 5_000, source: "model" },
+        hardMinTokens: 8_000,
+      });
+
+      expect(result.shouldBlock).toBe(true);
+    });
+
+    it("should handle zero tokens", () => {
+      const result = evaluateContextWindowGuard({
+        info: { tokens: 0, source: "model" },
+      });
+
+      expect(result.shouldWarn).toBe(false);
+      expect(result.shouldBlock).toBe(false);
+      expect(result.tokens).toBe(0);
+    });
+
+    it("should floor negative tokens to zero", () => {
+      const result = evaluateContextWindowGuard({
+        info: { tokens: -1000, source: "model" },
+      });
+
+      expect(result.tokens).toBe(0);
+    });
+
+    it("should ensure minimum threshold of 1", () => {
+      // When tokens is 5 and thresholds are floored to 1,
+      // 5 >= 1 so shouldWarn and shouldBlock are false
+      const result = evaluateContextWindowGuard({
+        info: { tokens: 5, source: "model" },
+        warnBelowTokens: 0,
+        hardMinTokens: -100,
+      });
+
+      // 5 is not < 1, so neither warn nor block
+      expect(result.shouldWarn).toBe(false);
+      expect(result.shouldBlock).toBe(false);
+    });
+
+    it("should correctly apply floored threshold of 1", () => {
+      // With tokens = 0, the condition (tokens > 0 && tokens < 1) is false
+      // because tokens > 0 is false
+      const result = evaluateContextWindowGuard({
+        info: { tokens: 0, source: "model" },
+        warnBelowTokens: 0,
+        hardMinTokens: -100,
+      });
+
+      expect(result.shouldWarn).toBe(false);
+      expect(result.shouldBlock).toBe(false);
+    });
+  });
+
+  describe("checkContextWindow", () => {
+    it("should combine resolution and evaluation", () => {
+      const result = checkContextWindow({
+        modelContextWindow: 100_000,
+      });
+
+      expect(result.tokens).toBe(100_000);
+      expect(result.source).toBe("model");
+      expect(result.shouldWarn).toBe(false);
+      expect(result.shouldBlock).toBe(false);
+    });
+
+    it("should warn for low config tokens", () => {
+      const result = checkContextWindow({
+        configContextTokens: 25_000,
+      });
+
+      expect(result.tokens).toBe(25_000);
+      expect(result.source).toBe("config");
+      expect(result.shouldWarn).toBe(true);
+      expect(result.shouldBlock).toBe(false);
+    });
+
+    it("should block for very low tokens", () => {
+      const result = checkContextWindow({
+        modelContextWindow: 8_000,
+      });
+
+      expect(result.shouldBlock).toBe(true);
+    });
+
+    it("should use all custom parameters", () => {
+      const result = checkContextWindow({
+        modelContextWindow: undefined,
+        configContextTokens: undefined,
+        defaultTokens: 50_000,
+        warnBelowTokens: 60_000,
+        hardMinTokens: 40_000,
+      });
+
+      expect(result.tokens).toBe(50_000);
+      expect(result.source).toBe("default");
+      expect(result.shouldWarn).toBe(true);
+      expect(result.shouldBlock).toBe(false);
+    });
+  });
+});
diff --git a/src/agent/session/storage.test.ts b/src/agent/session/storage.test.ts
new file mode 100644
index 00000000..ee0f9765
--- /dev/null
+++ b/src/agent/session/storage.test.ts
@@ -0,0 +1,277 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { existsSync, mkdirSync, rmSync, writeFileSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import {
+  resolveBaseDir,
+  resolveSessionDir,
+  resolveSessionPath,
+  ensureSessionDir,
+  readEntries,
+  appendEntry,
+  writeEntries,
+} from "./storage.js";
+import type { SessionEntry } from "./types.js";
+
+describe("session/storage", () => {
+  const testBaseDir = join(tmpdir(), `multica-session-test-${Date.now()}`);
+
+  beforeEach(() => {
+    if (existsSync(testBaseDir)) {
+      rmSync(testBaseDir, { recursive: true });
+    }
+    mkdirSync(testBaseDir, { recursive: true });
+  });
+
+  afterEach(() => {
+    if (existsSync(testBaseDir)) {
+      rmSync(testBaseDir, { recursive: true });
+    }
+  });
+
+  describe("resolveBaseDir", () => {
+    it("should return custom baseDir when provided", () => {
+      const result = resolveBaseDir({ baseDir: "/custom/path" });
+      expect(result).toBe("/custom/path");
+    });
+
+    it("should return default path when no options provided", () => {
+      const result = resolveBaseDir();
+      expect(result).toContain(".super-multica");
+      expect(result).toContain("sessions");
+    });
+
+    it("should return default path when options is empty", () => {
+      const result = resolveBaseDir({});
+      expect(result).toContain("sessions");
+    });
+  });
+
+  describe("resolveSessionDir", () => {
+    it("should return session directory path", () => {
+      const result = resolveSessionDir("test-session", { baseDir: testBaseDir });
+      expect(result).toBe(join(testBaseDir, "test-session"));
+    });
+
+    it("should handle session IDs with special characters", () => {
+      const result = resolveSessionDir("session-123-abc", { baseDir: testBaseDir });
+      expect(result).toBe(join(testBaseDir, "session-123-abc"));
+    });
+  });
+
+  describe("resolveSessionPath", () => {
+    it("should return path to session.jsonl file", () => {
+      const result = resolveSessionPath("test-session", { baseDir: testBaseDir });
+      expect(result).toBe(join(testBaseDir, "test-session", "session.jsonl"));
+    });
+  });
+
+  describe("ensureSessionDir", () => {
+    it("should create session directory if it does not exist", () => {
+      const sessionId = "new-session";
+      ensureSessionDir(sessionId, { baseDir: testBaseDir });
+
+      const dir = join(testBaseDir, sessionId);
+      expect(existsSync(dir)).toBe(true);
+    });
+
+    it("should not fail if directory already exists", () => {
+      const sessionId = "existing-session";
+      const dir = join(testBaseDir, sessionId);
+      mkdirSync(dir, { recursive: true });
+
+      expect(() => ensureSessionDir(sessionId, { baseDir: testBaseDir })).not.toThrow();
+      expect(existsSync(dir)).toBe(true);
+    });
+  });
+
+  describe("readEntries", () => {
+    it("should return empty array for non-existent session", () => {
+      const entries = readEntries("non-existent", { baseDir: testBaseDir });
+      expect(entries).toEqual([]);
+    });
+
+    it("should return empty array for empty file", () => {
+      const sessionId = "empty-session";
+      const dir = join(testBaseDir, sessionId);
+      mkdirSync(dir, { recursive: true });
+      writeFileSync(join(dir, "session.jsonl"), "");
+
+      const entries = readEntries(sessionId, { baseDir: testBaseDir });
+      expect(entries).toEqual([]);
+    });
+
+    it("should parse valid JSONL entries", () => {
+      const sessionId = "valid-session";
+      const dir = join(testBaseDir, sessionId);
+      mkdirSync(dir, { recursive: true });
+
+      const entry1: SessionEntry = {
+        type: "message",
+        message: { role: "user", content: "Hello" },
+        timestamp: 1000,
+      };
+      const entry2: SessionEntry = {
+        type: "message",
+        message: { role: "assistant", content: "Hi there" },
+        timestamp: 2000,
+      };
+
+      writeFileSync(
+        join(dir, "session.jsonl"),
+        `${JSON.stringify(entry1)}\n${JSON.stringify(entry2)}\n`
+      );
+
+      const entries = readEntries(sessionId, { baseDir: testBaseDir });
+      expect(entries).toHaveLength(2);
+      expect(entries[0]).toEqual(entry1);
+      expect(entries[1]).toEqual(entry2);
+    });
+
+    it("should skip malformed lines", () => {
+      const sessionId = "malformed-session";
+      const dir = join(testBaseDir, sessionId);
+      mkdirSync(dir, { recursive: true });
+
+      const validEntry: SessionEntry = {
+        type: "message",
+        message: { role: "user", content: "Valid" },
+        timestamp: 1000,
+      };
+
+      writeFileSync(
+        join(dir, "session.jsonl"),
+        `${JSON.stringify(validEntry)}\nnot valid json\n{broken: json}\n`
+      );
+
+      const entries = readEntries(sessionId, { baseDir: testBaseDir });
+      expect(entries).toHaveLength(1);
+      expect(entries[0]).toEqual(validEntry);
+    });
+
+    it("should handle meta entries", () => {
+      const sessionId = "meta-session";
+      const dir = join(testBaseDir, sessionId);
+      mkdirSync(dir, { recursive: true });
+
+      const metaEntry: SessionEntry = {
+        type: "meta",
+        meta: { provider: "anthropic", model: "claude-3" },
+        timestamp: 1000,
+      };
+
+      writeFileSync(join(dir, "session.jsonl"), `${JSON.stringify(metaEntry)}\n`);
+
+      const entries = readEntries(sessionId, { baseDir: testBaseDir });
+      expect(entries).toHaveLength(1);
+      expect(entries[0]).toEqual(metaEntry);
+    });
+
+    it("should handle compaction entries", () => {
+      const sessionId = "compaction-session";
+      const dir = join(testBaseDir, sessionId);
+      mkdirSync(dir, { recursive: true });
+
+      const compactionEntry: SessionEntry = {
+        type: "compaction",
+        removed: 10,
+        kept: 5,
+        timestamp: 1000,
+        tokensRemoved: 500,
+        tokensKept: 200,
+        reason: "tokens",
+      };
+
+      writeFileSync(join(dir, "session.jsonl"), `${JSON.stringify(compactionEntry)}\n`);
+
+      const entries = readEntries(sessionId, { baseDir: testBaseDir });
+      expect(entries).toHaveLength(1);
+      expect(entries[0]).toEqual(compactionEntry);
+    });
+  });
+
+  describe("appendEntry", () => {
+    it("should create file and append entry", async () => {
+      const sessionId = "append-session";
+      const entry: SessionEntry = {
+        type: "message",
+        message: { role: "user", content: "Hello" },
+        timestamp: 1000,
+      };
+
+      await appendEntry(sessionId, entry, { baseDir: testBaseDir });
+
+      const filePath = join(testBaseDir, sessionId, "session.jsonl");
+      expect(existsSync(filePath)).toBe(true);
+
+      const content = readFileSync(filePath, "utf8");
+      expect(content).toBe(`${JSON.stringify(entry)}\n`);
+    });
+
+    it("should append to existing file", async () => {
+      const sessionId = "append-existing";
+      const entry1: SessionEntry = {
+        type: "message",
+        message: { role: "user", content: "First" },
+        timestamp: 1000,
+      };
+      const entry2: SessionEntry = {
+        type: "message",
+        message: { role: "assistant", content: "Second" },
+        timestamp: 2000,
+      };
+
+      await appendEntry(sessionId, entry1, { baseDir: testBaseDir });
+      await appendEntry(sessionId, entry2, { baseDir: testBaseDir });
+
+      const entries = readEntries(sessionId, { baseDir: testBaseDir });
+      expect(entries).toHaveLength(2);
+      expect(entries[0]).toEqual(entry1);
+      expect(entries[1]).toEqual(entry2);
+    });
+  });
+
+  describe("writeEntries", () => {
+    it("should write all entries to file", async () => {
+      const sessionId = "write-session";
+      const entries: SessionEntry[] = [
+        { type: "message", message: { role: "user", content: "One" }, timestamp: 1000 },
+        { type: "message", message: { role: "assistant", content: "Two" }, timestamp: 2000 },
+      ];
+
+      await writeEntries(sessionId, entries, { baseDir: testBaseDir });
+
+      const readBack = readEntries(sessionId, { baseDir: testBaseDir });
+      expect(readBack).toHaveLength(2);
+      expect(readBack).toEqual(entries);
+    });
+
+    it("should overwrite existing entries", async () => {
+      const sessionId = "overwrite-session";
+
+      await writeEntries(
+        sessionId,
+        [{ type: "message", message: { role: "user", content: "Old" }, timestamp: 1000 }],
+        { baseDir: testBaseDir }
+      );
+
+      const newEntries: SessionEntry[] = [
+        { type: "message", message: { role: "user", content: "New" }, timestamp: 2000 },
+      ];
+      await writeEntries(sessionId, newEntries, { baseDir: testBaseDir });
+
+      const entries = readEntries(sessionId, { baseDir: testBaseDir });
+      expect(entries).toHaveLength(1);
+      expect((entries[0] as any).message.content).toBe("New");
+    });
+
+    it("should handle empty entries array", async () => {
+      const sessionId = "empty-write";
+      await writeEntries(sessionId, [], { baseDir: testBaseDir });
+
+      const filePath = join(testBaseDir, sessionId, "session.jsonl");
+      expect(existsSync(filePath)).toBe(true);
+      expect(readFileSync(filePath, "utf8")).toBe("");
+    });
+  });
+});