diff --git a/tests/lib/session-parser.test.ts b/tests/lib/session-parser.test.ts
new file mode 100644
index 0000000..5bb9e19
--- /dev/null
+++ b/tests/lib/session-parser.test.ts
@@ -0,0 +1,314 @@
+/**
+ * Tests for session-parser.ts
+ */
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { writeFileSync, mkdirSync, rmSync, statSync } from "fs";
+import { join } from "path";
+import { tmpdir } from "os";
+import { randomUUID } from "crypto";
+import {
+  parseSession,
+  parseSessionAsync,
+  findSessionFiles,
+  parseAllSessions,
+} from "../../src/lib/session-parser.js";
+
+// ── Helpers ────────────────────────────────────────────────────────────────
+
+function tmpDir(): string {
+  const dir = join(tmpdir(), `preflight-test-${randomUUID()}`);
+  mkdirSync(dir, { recursive: true });
+  return dir;
+}
+
+function writeJsonl(dir: string, name: string, records: any[]): string {
+  const p = join(dir, name);
+  writeFileSync(p, records.map((r) => JSON.stringify(r)).join("\n") + "\n");
+  return p;
+}
+
+// ── Fixtures ───────────────────────────────────────────────────────────────
+
+const SUMMARY_RECORD = {
+  type: "summary",
+  sessionId: "sess-001",
+  gitBranch: "main",
+};
+
+const USER_PROMPT = {
+  type: "user",
+  timestamp: "2026-03-16T10:00:00Z",
+  message: { content: "Fix the login bug" },
+};
+
+const ASSISTANT_TEXT = {
+  type: "assistant",
+  timestamp: "2026-03-16T10:00:05Z",
+  model: "claude-3.5-sonnet",
+  message: { content: [{ type: "text", text: "I'll fix the login bug now." }] },
+};
+
+const ASSISTANT_WITH_TOOL = {
+  type: "assistant",
+  timestamp: "2026-03-16T10:00:10Z",
+  message: {
+    content: [
+      { type: "text", text: "Let me read the file." },
+      { type: "tool_use", name: "Read", input: { path: "src/login.ts" } },
+    ],
+  },
+};
+
+const ASSISTANT_WITH_SUBAGENT = {
+  type: "assistant",
+  timestamp: "2026-03-16T10:00:15Z",
+  message: {
+    content: [
+      { type: "tool_use", name: "Task", input: { task: "refactor auth" } },
+    ],
+  },
+};
+
+const TOOL_RESULT_OK = {
+  type: "tool_result",
+  timestamp: "2026-03-16T10:00:12Z",
+  tool_use_id: "tu-1",
+  content: "file contents here",
+};
+
+const TOOL_RESULT_ERROR = {
+  type: "tool_result",
+  timestamp: "2026-03-16T10:00:12Z",
+  tool_use_id: "tu-2",
+  is_error: true,
+  content: "ENOENT: no such file",
+};
+
+const COMPACTION = {
+  type: "system",
+  timestamp: "2026-03-16T12:00:00Z",
+  subtype: "compaction",
+  message: { content: "Context compacted" },
+};
+
+const CORRECTION_PROMPT = {
+  type: "user",
+  timestamp: "2026-03-16T10:00:20Z",
+  message: { content: "No, I meant the signup page, not login" },
+};
+
+// ── Tests ──────────────────────────────────────────────────────────────────
+
+describe("session-parser", () => {
+  let dir: string;
+
+  beforeEach(() => {
+    dir = tmpDir();
+  });
+
+  afterEach(() => {
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  describe("parseSession (sync)", () => {
+    it("parses user prompts", () => {
+      const f = writeJsonl(dir, "test.jsonl", [USER_PROMPT]);
+      const events = parseSession(f, "/test/project", "project");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("prompt");
+      expect(events[0].content).toBe("Fix the login bug");
+      expect(events[0].timestamp).toBe("2026-03-16T10:00:00.000Z");
+    });
+
+    it("parses assistant text responses", () => {
+      const f = writeJsonl(dir, "test.jsonl", [ASSISTANT_TEXT]);
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("assistant");
+      expect(events[0].content).toContain("fix the login bug");
+      const meta = JSON.parse(events[0].metadata);
+      expect(meta.model).toBe("claude-3.5-sonnet");
+    });
+
+    it("extracts tool_call events from assistant messages", () => {
+      const f = writeJsonl(dir, "test.jsonl", [ASSISTANT_WITH_TOOL]);
+      const events = parseSession(f, "/test", "test");
+      const toolEvents = events.filter((e) => e.type === "tool_call");
+      expect(toolEvents).toHaveLength(1);
+      expect(toolEvents[0].content).toContain("Read");
+    });
+
+    it("identifies sub_agent_spawn from Task tool", () => {
+      const f = writeJsonl(dir, "test.jsonl", [ASSISTANT_WITH_SUBAGENT]);
+      const events = parseSession(f, "/test", "test");
+      const spawns = events.filter((e) => e.type === "sub_agent_spawn");
+      expect(spawns).toHaveLength(1);
+      expect(spawns[0].content).toContain("Task");
+    });
+
+    it("captures error tool results", () => {
+      const f = writeJsonl(dir, "test.jsonl", [TOOL_RESULT_ERROR]);
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("error");
+      expect(events[0].content).toContain("ENOENT");
+    });
+
+    it("ignores successful tool results", () => {
+      const f = writeJsonl(dir, "test.jsonl", [TOOL_RESULT_OK]);
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(0);
+    });
+
+    it("detects compaction events", () => {
+      const f = writeJsonl(dir, "test.jsonl", [COMPACTION]);
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("compaction");
+    });
+
+    it("detects corrections after assistant messages", () => {
+      const f = writeJsonl(dir, "test.jsonl", [
+        USER_PROMPT,
+        ASSISTANT_TEXT,
+        CORRECTION_PROMPT,
+      ]);
+      const events = parseSession(f, "/test", "test");
+      const corrections = events.filter((e) => e.type === "correction");
+      expect(corrections).toHaveLength(1);
+      expect(corrections[0].content).toContain("signup page");
+    });
+
+    it("reads branch and sessionId from summary records", () => {
+      const f = writeJsonl(dir, "test.jsonl", [SUMMARY_RECORD, USER_PROMPT]);
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].branch).toBe("main");
+      expect(events[0].session_id).toBe("sess-001");
+    });
+
+    it("handles empty files", () => {
+      const f = writeJsonl(dir, "test.jsonl", []);
+      writeFileSync(f, "");
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(0);
+    });
+
+    it("skips malformed JSON lines gracefully", () => {
+      const f = join(dir, "bad.jsonl");
+      writeFileSync(f, '{"type":"user","timestamp":"2026-01-01T00:00:00Z","message":{"content":"hi"}}\n{bad json\n');
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("prompt");
+    });
+
+    it("normalizes epoch timestamps", () => {
+      const record = {
+        type: "user",
+        timestamp: 1742122800, // epoch seconds
+        message: { content: "test epoch" },
+      };
+      const f = writeJsonl(dir, "test.jsonl", [record]);
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(1);
+      // Should be a valid ISO string
+      expect(events[0].timestamp).toMatch(/^\d{4}-\d{2}-\d{2}T/);
+    });
+
+    it("handles string content (not array) in messages", () => {
+      const record = {
+        type: "user",
+        timestamp: "2026-03-16T10:00:00Z",
+        message: { content: "plain string content" },
+      };
+      const f = writeJsonl(dir, "test.jsonl", [record]);
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].content).toBe("plain string content");
+    });
+
+    it("handles user message with no content gracefully", () => {
+      const record = {
+        type: "user",
+        timestamp: "2026-03-16T10:00:00Z",
+        message: { content: "" },
+      };
+      const f = writeJsonl(dir, "test.jsonl", [record]);
+      const events = parseSession(f, "/test", "test");
+      expect(events).toHaveLength(0); // empty content should be skipped
+    });
+  });
+
+  describe("parseSessionAsync", () => {
+    it("produces same results as sync parser", async () => {
+      const records = [SUMMARY_RECORD, USER_PROMPT, ASSISTANT_TEXT, ASSISTANT_WITH_TOOL, TOOL_RESULT_ERROR, COMPACTION];
+      const f = writeJsonl(dir, "test.jsonl", records);
+      const syncEvents = parseSession(f, "/test", "test");
+      const asyncEvents = await parseSessionAsync(f, "/test", "test");
+
+      expect(asyncEvents.length).toBe(syncEvents.length);
+      for (let i = 0; i < syncEvents.length; i++) {
+        expect(asyncEvents[i].type).toBe(syncEvents[i].type);
+        expect(asyncEvents[i].content).toBe(syncEvents[i].content);
+      }
+    });
+  });
+
+  describe("findSessionFiles", () => {
+    it("finds .jsonl files in directory", () => {
+      writeJsonl(dir, "session-a.jsonl", [USER_PROMPT]);
+      writeJsonl(dir, "session-b.jsonl", [USER_PROMPT]);
+      writeFileSync(join(dir, "notes.txt"), "not a session");
+      const files = findSessionFiles(dir);
+      expect(files).toHaveLength(2);
+      expect(files.every((f) => f.path.endsWith(".jsonl"))).toBe(true);
+    });
+
+    it("finds subagent session files", () => {
+      const subDir = join(dir, "parent-uuid", "subagents");
+      mkdirSync(subDir, { recursive: true });
+      writeJsonl(subDir, "sub-agent.jsonl", [USER_PROMPT]);
+      const files = findSessionFiles(dir);
+      expect(files).toHaveLength(1);
+      expect(files[0].sessionId).toBe("sub-agent");
+    });
+
+    it("returns empty for nonexistent directory", () => {
+      const files = findSessionFiles("/nonexistent/path");
+      expect(files).toHaveLength(0);
+    });
+  });
+
+  describe("parseAllSessions", () => {
+    it("parses all session files and sorts by timestamp", () => {
+      const early = {
+        type: "user",
+        timestamp: "2026-03-15T08:00:00Z",
+        message: { content: "early" },
+      };
+      const late = {
+        type: "user",
+        timestamp: "2026-03-16T20:00:00Z",
+        message: { content: "late" },
+      };
+      writeJsonl(dir, "sess-late.jsonl", [late]);
+      writeJsonl(dir, "sess-early.jsonl", [early]);
+      const events = parseAllSessions(dir);
+      expect(events).toHaveLength(2);
+      expect(events[0].content).toBe("early");
+      expect(events[1].content).toBe("late");
+    });
+
+    it("filters by since date", () => {
+      const old = {
+        type: "user",
+        timestamp: "2026-01-01T00:00:00Z",
+        message: { content: "old" },
+      };
+      const p = writeJsonl(dir, "old.jsonl", [old]);
+      // Set mtime to the past
+      const events = parseAllSessions(dir, { since: new Date("2027-01-01") });
+      expect(events).toHaveLength(0);
+    });
+  });
+});