diff --git a/tests/lib/session-parser.test.ts b/tests/lib/session-parser.test.ts
new file mode 100644
index 0000000..4aab007
--- /dev/null
+++ b/tests/lib/session-parser.test.ts
@@ -0,0 +1,290 @@
+/**
+ * Tests for session-parser.ts — JSONL session parsing into timeline events.
+ */
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { mkdtempSync, writeFileSync, mkdirSync, rmSync, statSync } from "fs";
+import { join } from "path";
+import { tmpdir } from "os";
+import {
+  findSessionFiles,
+  parseSession,
+  parseSessionAsync,
+  parseAllSessions,
+  type TimelineEvent,
+} from "../../src/lib/session-parser.js";
+
+// ── Helpers ────────────────────────────────────────────────────────────────
+
+function tmpDir(): string {
+  return mkdtempSync(join(tmpdir(), "preflight-test-"));
+}
+
+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;
+}
+
+// ── findSessionFiles ───────────────────────────────────────────────────────
+
+describe("findSessionFiles", () => {
+  let dir: string;
+  afterEach(() => dir && rmSync(dir, { recursive: true, force: true }));
+
+  it("returns empty array for non-existent directory", () => {
+    expect(findSessionFiles("/tmp/does-not-exist-xyz")).toEqual([]);
+  });
+
+  it("discovers .jsonl files at top level", () => {
+    dir = tmpDir();
+    writeFileSync(join(dir, "abc.jsonl"), "{}");
+    writeFileSync(join(dir, "def.jsonl"), "{}");
+    writeFileSync(join(dir, "readme.txt"), "hi");
+
+    const files = findSessionFiles(dir);
+    expect(files).toHaveLength(2);
+    expect(files.map((f) => f.sessionId).sort()).toEqual(["abc", "def"]);
+  });
+
+  it("discovers subagent .jsonl files", () => {
+    dir = tmpDir();
+    const subDir = join(dir, "session-1", "subagents");
+    mkdirSync(subDir, { recursive: true });
+    writeFileSync(join(subDir, "sub-agent-1.jsonl"), "{}");
+
+    const files = findSessionFiles(dir);
+    expect(files).toHaveLength(1);
+    expect(files[0].sessionId).toBe("sub-agent-1");
+  });
+});
+
+// ── parseSession ───────────────────────────────────────────────────────────
+
+describe("parseSession", () => {
+  let dir: string;
+  afterEach(() => dir && rmSync(dir, { recursive: true, force: true }));
+
+  it("parses user prompts", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      { type: "user", message: { content: "Add a login page" }, timestamp: "2026-01-15T10:00:00Z" },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events).toHaveLength(1);
+    expect(events[0].type).toBe("prompt");
+    expect(events[0].content).toBe("Add a login page");
+    expect(events[0].timestamp).toBe("2026-01-15T10:00:00.000Z");
+  });
+
+  it("parses assistant text responses", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      { type: "assistant", message: { content: "Done!" }, timestamp: "2026-01-15T10:01:00Z" },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events).toHaveLength(1);
+    expect(events[0].type).toBe("assistant");
+  });
+
+  it("parses assistant content blocks (array format)", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      {
+        type: "assistant",
+        message: {
+          content: [
+            { type: "text", text: "Here's the code" },
+            { type: "tool_use", name: "Write", input: { path: "foo.ts" } },
+          ],
+        },
+        timestamp: "2026-01-15T10:01:00Z",
+      },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    // Should produce: assistant text + tool_call
+    expect(events).toHaveLength(2);
+    expect(events[0].type).toBe("assistant");
+    expect(events[1].type).toBe("tool_call");
+    expect(events[1].content).toContain("Write");
+  });
+
+  it("detects correction patterns", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      { type: "assistant", message: { content: "I created the component" }, timestamp: "2026-01-15T10:00:00Z" },
+      { type: "user", message: { content: "No, I meant the other one" }, timestamp: "2026-01-15T10:01:00Z" },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    const userEvent = events.find((e) => e.type === "correction" || e.type === "prompt");
+    expect(userEvent?.type).toBe("correction");
+  });
+
+  it("detects sub-agent spawns (Task tool)", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      {
+        type: "assistant",
+        message: {
+          content: [{ type: "tool_use", name: "Task", input: { description: "refactor auth" } }],
+        },
+        timestamp: "2026-01-15T10:00:00Z",
+      },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events).toHaveLength(1);
+    expect(events[0].type).toBe("sub_agent_spawn");
+  });
+
+  it("detects dispatch_agent as sub-agent spawn", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      {
+        type: "assistant",
+        message: {
+          content: [{ type: "tool_use", name: "dispatch_agent", input: {} }],
+        },
+        timestamp: "2026-01-15T10:00:00Z",
+      },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events[0].type).toBe("sub_agent_spawn");
+  });
+
+  it("parses tool_result errors", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      { type: "tool_result", is_error: true, content: "ENOENT: file not found", timestamp: "2026-01-15T10:00:00Z" },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events).toHaveLength(1);
+    expect(events[0].type).toBe("error");
+  });
+
+  it("parses compaction events", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      { type: "system", message: { content: "Context compacted to save tokens" }, timestamp: "2026-01-15T10:00:00Z" },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events).toHaveLength(1);
+    expect(events[0].type).toBe("compaction");
+  });
+
+  it("extracts branch from summary records", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      { type: "summary", gitBranch: "feat/login", sessionId: "sess-42" },
+      { type: "user", message: { content: "Hello" }, timestamp: "2026-01-15T10:00:00Z" },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events).toHaveLength(1);
+    expect(events[0].branch).toBe("feat/login");
+    expect(events[0].session_id).toBe("sess-42");
+  });
+
+  it("handles malformed JSON lines gracefully", () => {
+    dir = tmpDir();
+    const file = join(dir, "bad.jsonl");
+    writeFileSync(file, '{"type":"user","message":{"content":"ok"},"timestamp":"2026-01-15T10:00:00Z"}\nNOT JSON\n');
+
+    // Should not throw, should parse the valid line
+    const events = parseSession(file, "/proj", "proj");
+    expect(events).toHaveLength(1);
+  });
+
+  it("normalizes epoch timestamps", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      { type: "user", message: { content: "test" }, timestamp: 1705312800 },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events[0].timestamp).toMatch(/^\d{4}-\d{2}-\d{2}T/);
+  });
+
+  it("skips empty user messages", () => {
+    dir = tmpDir();
+    const file = writeJsonl(dir, "s1.jsonl", [
+      { type: "user", message: { content: "" }, timestamp: "2026-01-15T10:00:00Z" },
+    ]);
+
+    const events = parseSession(file, "/proj", "proj");
+    expect(events).toHaveLength(0);
+  });
+});
+
+// ── parseSessionAsync ──────────────────────────────────────────────────────
+
+describe("parseSessionAsync", () => {
+  let dir: string;
+  afterEach(() => dir && rmSync(dir, { recursive: true, force: true }));
+
+  it("produces same results as sync parser", async () => {
+    dir = tmpDir();
+    const records = [
+      { type: "summary", gitBranch: "main", sessionId: "s1" },
+      { type: "user", message: { content: "Hello world" }, timestamp: "2026-01-15T10:00:00Z" },
+      { type: "assistant", message: { content: "Hi there" }, timestamp: "2026-01-15T10:00:01Z" },
+      { type: "user", message: { content: "No, wrong answer" }, timestamp: "2026-01-15T10:00:02Z" },
+    ];
+    const file = writeJsonl(dir, "s1.jsonl", records);
+
+    const syncEvents = parseSession(file, "/proj", "proj");
+    const asyncEvents = await parseSessionAsync(file, "/proj", "proj");
+
+    expect(asyncEvents).toHaveLength(syncEvents.length);
+    // Types should match (ids will differ)
+    expect(asyncEvents.map((e) => e.type)).toEqual(syncEvents.map((e) => e.type));
+    expect(asyncEvents.map((e) => e.content)).toEqual(syncEvents.map((e) => e.content));
+  });
+});
+
+// ── parseAllSessions ───────────────────────────────────────────────────────
+
+describe("parseAllSessions", () => {
+  let dir: string;
+  afterEach(() => dir && rmSync(dir, { recursive: true, force: true }));
+
+  it("parses all jsonl files and sorts by timestamp", () => {
+    dir = tmpDir();
+    writeJsonl(dir, "a.jsonl", [
+      { type: "user", message: { content: "second" }, timestamp: "2026-01-15T10:01:00Z" },
+    ]);
+    writeJsonl(dir, "b.jsonl", [
+      { type: "user", message: { content: "first" }, timestamp: "2026-01-15T10:00:00Z" },
+    ]);
+
+    const events = parseAllSessions(dir);
+    expect(events).toHaveLength(2);
+    expect(events[0].content).toBe("first");
+    expect(events[1].content).toBe("second");
+  });
+
+  it("filters by since date", () => {
+    dir = tmpDir();
+    const oldFile = writeJsonl(dir, "old.jsonl", [
+      { type: "user", message: { content: "old" }, timestamp: "2025-01-01T00:00:00Z" },
+    ]);
+    // Touch the old file to make its mtime old
+    const past = new Date("2025-01-01");
+    const { utimesSync } = require("fs");
+    utimesSync(oldFile, past, past);
+
+    writeJsonl(dir, "new.jsonl", [
+      { type: "user", message: { content: "new" }, timestamp: "2026-01-15T10:00:00Z" },
+    ]);
+
+    const events = parseAllSessions(dir, { since: new Date("2026-01-01") });
+    expect(events).toHaveLength(1);
+    expect(events[0].content).toBe("new");
+  });
+});