diff --git a/tests/lib/session-parser.test.ts b/tests/lib/session-parser.test.ts
new file mode 100644
index 0000000..13d1b7b
--- /dev/null
+++ b/tests/lib/session-parser.test.ts
@@ -0,0 +1,314 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { mkdtempSync, writeFileSync, mkdirSync, rmSync } from "fs";
+import { join } from "path";
+import { tmpdir } from "os";
+import { parseSession, findSessionFiles } from "../../src/lib/session-parser.js";
+
+// ── Test Helpers ───────────────────────────────────────────────────────────
+
+function makeTmpDir(): string {
+  return mkdtempSync(join(tmpdir(), "preflight-test-"));
+}
+
+function writeJsonl(dir: string, filename: string, records: any[]): string {
+  const path = join(dir, filename);
+  writeFileSync(path, records.map((r) => JSON.stringify(r)).join("\n") + "\n");
+  return path;
+}
+
+// ── Tests ──────────────────────────────────────────────────────────────────
+
+describe("session-parser", () => {
+  let tmpDir: string;
+
+  beforeEach(() => {
+    tmpDir = makeTmpDir();
+  });
+
+  afterEach(() => {
+    rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  describe("findSessionFiles", () => {
+    it("returns empty array for non-existent directory", () => {
+      const result = findSessionFiles("/tmp/does-not-exist-xyz");
+      expect(result).toEqual([]);
+    });
+
+    it("finds .jsonl files in a directory", () => {
+      writeFileSync(join(tmpDir, "session-1.jsonl"), "{}");
+      writeFileSync(join(tmpDir, "session-2.jsonl"), "{}");
+      writeFileSync(join(tmpDir, "readme.txt"), "ignored");
+
+      const result = findSessionFiles(tmpDir);
+      expect(result).toHaveLength(2);
+      expect(result.map((r) => r.sessionId).sort()).toEqual(["session-1", "session-2"]);
+    });
+
+    it("finds subagent JSONL files", () => {
+      const subDir = join(tmpDir, "parent-session", "subagents");
+      mkdirSync(subDir, { recursive: true });
+      writeFileSync(join(subDir, "sub-1.jsonl"), "{}");
+
+      const result = findSessionFiles(tmpDir);
+      expect(result).toHaveLength(1);
+      expect(result[0].sessionId).toBe("sub-1");
+    });
+
+    it("returns mtime for each file", () => {
+      writeFileSync(join(tmpDir, "test.jsonl"), "{}");
+      const result = findSessionFiles(tmpDir);
+      expect(result[0].mtime).toBeInstanceOf(Date);
+    });
+  });
+
+  describe("parseSession", () => {
+    it("parses user prompts into timeline events", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "user", message: { content: "Hello world" }, timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("prompt");
+      expect(events[0].content).toBe("Hello world");
+      expect(events[0].project).toBe("/test");
+      expect(events[0].project_name).toBe("test");
+    });
+
+    it("parses assistant responses", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "assistant", message: { content: "I'll help you" }, timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("assistant");
+      expect(events[0].content).toBe("I'll help you");
+    });
+
+    it("handles content block arrays", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        {
+          type: "user",
+          message: { content: [{ type: "text", text: "block one" }, { type: "text", text: "block two" }] },
+          timestamp: "2025-01-01T00:00:00Z",
+        },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].content).toBe("block one\nblock two");
+    });
+
+    it("detects corrections after assistant messages", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "assistant", message: { content: "Here's the code" }, timestamp: "2025-01-01T00:00:00Z" },
+        { type: "user", message: { content: "No, that's wrong" }, timestamp: "2025-01-01T00:01:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      const correction = events.find((e) => e.type === "correction");
+      expect(correction).toBeDefined();
+      expect(correction!.content).toBe("No, that's wrong");
+    });
+
+    it("does not flag first user message as correction", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "user", message: { content: "No, actually do this instead" }, timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].type).toBe("prompt");
+    });
+
+    it("extracts tool calls from assistant messages", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        {
+          type: "assistant",
+          message: {
+            content: [
+              { type: "text", text: "Let me check" },
+              { type: "tool_use", name: "Read", input: { path: "/foo" } },
+            ],
+          },
+          timestamp: "2025-01-01T00:00:00Z",
+        },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      const toolCall = events.find((e) => e.type === "tool_call");
+      expect(toolCall).toBeDefined();
+      expect(toolCall!.content).toContain("Read");
+    });
+
+    it("detects sub_agent_spawn for Task tool", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        {
+          type: "assistant",
+          message: {
+            content: [{ type: "tool_use", name: "Task", input: { description: "do stuff" } }],
+          },
+          timestamp: "2025-01-01T00:00:00Z",
+        },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events.some((e) => e.type === "sub_agent_spawn")).toBe(true);
+    });
+
+    it("detects sub_agent_spawn for dispatch_agent tool", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        {
+          type: "assistant",
+          message: {
+            content: [{ type: "tool_use", name: "dispatch_agent", input: {} }],
+          },
+          timestamp: "2025-01-01T00:00:00Z",
+        },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events.some((e) => e.type === "sub_agent_spawn")).toBe(true);
+    });
+
+    it("detects errors in tool_result", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "tool_result", is_error: true, content: "Command failed", timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("error");
+    });
+
+    it("detects compaction events", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "system", message: { content: "Context compacted" }, timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].type).toBe("compaction");
+    });
+
+    it("handles summary records (branch + session id)", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "summary", gitBranch: "feat/cool", sessionId: "abc123" },
+        { type: "user", message: { content: "hi" }, timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events).toHaveLength(1);
+      expect(events[0].branch).toBe("feat/cool");
+      expect(events[0].session_id).toBe("abc123");
+    });
+
+    it("skips malformed JSON lines gracefully", () => {
+      const path = join(tmpDir, "test.jsonl");
+      writeFileSync(
+        path,
+        '{"type":"user","message":{"content":"valid"},"timestamp":"2025-01-01T00:00:00Z"}\nthis is not json\n{"type":"user","message":{"content":"also valid"},"timestamp":"2025-01-01T00:01:00Z"}\n',
+      );
+
+      const events = parseSession(path, "/test", "test");
+      expect(events).toHaveLength(2);
+    });
+
+    it("handles empty file", () => {
+      const path = join(tmpDir, "empty.jsonl");
+      writeFileSync(path, "");
+
+      const events = parseSession(path, "/test", "test");
+      expect(events).toHaveLength(0);
+    });
+
+    it("normalizes epoch timestamps", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "user", message: { content: "hello" }, timestamp: 1704067200 },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].timestamp).toBe("2024-01-01T00:00:00.000Z");
+    });
+
+    it("normalizes epoch millisecond timestamps", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "user", message: { content: "hello" }, timestamp: 1704067200000 },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].timestamp).toBe("2024-01-01T00:00:00.000Z");
+    });
+
+    it("generates unique ids for each event", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "user", message: { content: "one" }, timestamp: "2025-01-01T00:00:00Z" },
+        { type: "user", message: { content: "two" }, timestamp: "2025-01-01T00:01:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].id).not.toBe(events[1].id);
+    });
+
+    it("creates content_preview from first line", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "user", message: { content: "first line\nsecond line\nthird line" }, timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].content_preview).toBe("first line");
+    });
+
+    it("truncates long previews", () => {
+      const longText = "a".repeat(200);
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "user", message: { content: longText }, timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].content_preview.length).toBeLessThanOrEqual(121); // 120 + "…"
+    });
+
+    it("handles tool_result with stderr pattern as error", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "tool_result", content: "stderr: something failed", timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].type).toBe("error");
+    });
+
+    it("ignores non-error tool_result records", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "tool_result", content: "file contents here", timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events).toHaveLength(0);
+    });
+
+    it("records source_file and source_line", () => {
+      const path = writeJsonl(tmpDir, "test.jsonl", [
+        { type: "user", message: { content: "hi" }, timestamp: "2025-01-01T00:00:00Z" },
+      ]);
+
+      const events = parseSession(path, "/test", "test");
+      expect(events[0].source_file).toBe(path);
+      expect(events[0].source_line).toBeGreaterThan(0);
+    });
+
+    it("handles multiple correction patterns", () => {
+      const corrections = ["undo that", "i meant something else", "actually do this", "not that one"];
+      for (const text of corrections) {
+        const path = writeJsonl(tmpDir, `test-${text.replace(/\s/g, "-")}.jsonl`, [
+          { type: "assistant", message: { content: "done" }, timestamp: "2025-01-01T00:00:00Z" },
+          { type: "user", message: { content: text }, timestamp: "2025-01-01T00:01:00Z" },
+        ]);
+
+        const events = parseSession(path, "/test", "test");
+        const hasCorrection = events.some((e) => e.type === "correction");
+        expect(hasCorrection, `"${text}" should be detected as correction`).toBe(true);
+      }
+    });
+  });
+});