diff --git a/extension/README.md b/extension/README.md
index 7a0f0c90..7494c765 100644
--- a/extension/README.md
+++ b/extension/README.md
@@ -86,7 +86,7 @@ also appear in the editor title bar, the Explorer, or **Project Options**.
 | **Change Main File...** | Pick the main file from the workspace |
 | **Change Platform...** | Build the project for another platform |
 | **Detect Projects** | Scan the folder for projects and platforms |
-| **Add Launch Configuration** | Write a run configuration to `.vscode/launch.json` |
+| **Add Launch Configuration** | Write a run configuration to `.vscode/launch.json`; <kbd>F5</kbd> debugs it, with step back |
 | **Project Options** | Open the project menu |
 | **Build** | Build without running |
 | **Run** | Build and run in the emulator |
diff --git a/extension/docs/QUICKSTART.md b/extension/docs/QUICKSTART.md
index 6b0dcbff..7cff79ab 100644
--- a/extension/docs/QUICKSTART.md
+++ b/extension/docs/QUICKSTART.md
@@ -88,7 +88,7 @@ back, click the status bar and choose **Run Main File**.
 
 To keep a list of programs to switch between, click the status bar and
 choose **Add Launch Configuration**. The program then appears in the
-**Run and Debug** view's list, and <kbd>F5</kbd> runs the one you chose.
+**Run and Debug** view's list, and <kbd>F5</kbd> debugs the one you chose.
 
 **A folder of small programs**, like a set of exercises, has no main
 file. **Run** runs the program in the editor you're looking at. The
diff --git a/extension/docs/emulator.md b/extension/docs/emulator.md
index 43080af4..ca3e8b14 100644
--- a/extension/docs/emulator.md
+++ b/extension/docs/emulator.md
@@ -43,6 +43,49 @@ A build that fails leaves the last good version running.
 Some programs end, such as a BASIC program. Then the panel says
 **Halted** and the reason. Click **Run** to start again.
 
+## Go back in time
+
+The emulator records as it runs. While it's paused, a timeline appears
+under the screen. Drag it to see any recorded frame. **Resume** runs on
+from the frame you're looking at. Pressing a key there starts a new
+future and drops the one that was recorded.
+
+The recording keeps about the last 50 seconds. The NES saves bigger
+states, so it keeps about 10 seconds.
+
+## Debug
+
+Press <kbd>F5</kbd> to build the program and debug it. Press
+<kbd>Ctrl</kbd>+<kbd>F5</kbd> (**Run Without Debugging**) to just run it.
+
+- **Breakpoints:** click left of a line number in C or assembly. You can
+  also add a breakpoint on a function by name (**+** in the Breakpoints
+  view), or on an address in the Disassembly view. A condition such as
+  `A == 3` or `[score] > 100` makes the breakpoint stop only when it's true.
+- **Stepping:** Step Over, Step Into and Step Out go by source line. In the
+  Disassembly view they go by instruction.
+- **Step Back** and **Reverse Continue** run backwards through the
+  recording, to the previous line or the previous breakpoint hit.
+- **Variables** shows the CPU registers. **Watch** and hovers take the
+  same expressions as conditions: registers, symbols, `[addr]` for a byte
+  of memory, `#mem16[addr]` for a word.
+- The **Debug Console** takes the commands of `8bws run -e`, such as
+  `mem $0200 32`, `hist 10`, `back 5` and `rbreak main`. Type `help` to
+  list them.
+
+A launch configuration can also set:
+
+| Setting | What it does |
+|---|---|
+| `stopOnEntry` | Stop before the first instruction instead of running |
+| `script` | Debug Console commands to run once the program loads, such as `"break main"` |
+
+While you debug, a rebuild doesn't restart the program. Press
+<kbd>F5</kbd> again to debug the new build.
+
+Some platforms, such as the Atari 2600 and Verilog, can only stop
+between frames. There, breakpoints and steps work a frame at a time.
+
 ## Sound
 
 The emulator plays sound through the panel. Audio starts on your first click
diff --git a/extension/docs/projects.md b/extension/docs/projects.md
index 90e00c4f..07ef1304 100644
--- a/extension/docs/projects.md
+++ b/extension/docs/projects.md
@@ -78,7 +78,7 @@ To switch between programs with <kbd>F5</kbd>:
 2. Click the status bar and choose **Add Launch Configuration**.
 
 The program appears in the **Run and Debug** view's list. Choose it there
-and press <kbd>F5</kbd> to build and run it. A launch configuration can
+and press <kbd>F5</kbd> to build and debug it. A launch configuration can
 also name another platform, so one program can run on `c64` and `vic20`:
 
 ```json
@@ -91,7 +91,8 @@ also name another platform, so one program can run on `c64` and `vic20`:
 }
 ```
 
-<kbd>F5</kbd> runs the program but doesn't debug it yet.
+<kbd>F5</kbd> builds and debugs the program; <kbd>Ctrl</kbd>+<kbd>F5</kbd>
+runs it without the debugger. See [Debug](emulator.md#debug).
 
 ## Where your choices are saved
 
diff --git a/extension/notes/PLAN.md b/extension/notes/PLAN.md
index d554629e..cf2dc490 100644
--- a/extension/notes/PLAN.md
+++ b/extension/notes/PLAN.md
@@ -1647,8 +1647,11 @@ debugger shouldn't become a third.
   `DebugService` and answers `debug(method, ...)`; its frame loop runs
   through the controller, and every stop is a `stopped` event. The adapter
   is `src/tools/dapsession.ts`, shared with `8bws dap`;
-  `extension/src/debugbackend.ts` is its RPC backend. Not yet wired into
-  `extension.ts`.)* The Debug Adapter (next
+  `extension/src/debugbackend.ts` is its RPC backend. F5 debugs; Ctrl+F5
+  (`noDebug`) runs as before. A debug launch builds, starts the worker
+  paused, and sends the listings with `setBuild`. Rebuilds don't reload
+  under the debugger; a plain Run ends the session. The panel's timeline
+  slider (shown while stopped) calls `seekFrame`.)* The Debug Adapter (next
   section) runs in the extension host and translates DAP to RPC. DAP has
   reverse debugging built in: report `supportsStepBack`, and handle
   `stepBack` and `reverseContinue`. Scrubbing (`seekFrame`) is a timeline
diff --git a/extension/package.json b/extension/package.json
index 16d461b0..7c1ab897 100644
--- a/extension/package.json
+++ b/extension/package.json
@@ -434,6 +434,13 @@
         "contents": "Make a program for a classic console or computer.\n[New 8bitworkshop Project](command:8bitworkshop.newProject)\n[Open 8bitworkshop Example](command:8bitworkshop.openExample)"
       }
     ],
+    "breakpoints": [
+      { "language": "c" },
+      { "language": "cpp" },
+      { "language": "8bws-6502" },
+      { "language": "8bws-z80" },
+      { "language": "8bws-6809" }
+    ],
     "debuggers": [
       {
         "type": "8bitworkshop",
@@ -453,6 +460,15 @@
               "tool": {
                 "type": "string",
                 "description": "Tool for the main file, if not the usual one."
+              },
+              "stopOnEntry": {
+                "type": "boolean",
+                "description": "Stop before the program's first instruction instead of running.",
+                "default": false
+              },
+              "script": {
+                "type": "string",
+                "description": "Commands to run once the program is loaded, as in the Debug Console (e.g. \"break main; key SPACE\")."
               }
             }
           }
diff --git a/extension/src/emulatorpanel.ts b/extension/src/emulatorpanel.ts
index d0262b65..02a64921 100644
--- a/extension/src/emulatorpanel.ts
+++ b/extension/src/emulatorpanel.ts
@@ -11,6 +11,8 @@ export interface PanelEvents {
   onKey(key: number, code: number, flags: number): void;
   /** the user showed or hid the controls bar */
   onControlsVisible(visible: boolean): void;
+  /** the user dragged the timeline to a recorded frame */
+  onSeek?(frame: number): void;
   onVisible(visible: boolean): void;
   onDispose(): void;
 }
@@ -29,6 +31,7 @@ export class EmulatorPanel {
       if (msg.type === 'key') this.events.onKey(msg.key, msg.code, msg.flags);
       else if (msg.type === 'frameDone') this.frameInFlight = false;
       else if (msg.type === 'controlsVisible') this.events.onControlsVisible(!!msg.visible);
+      else if (msg.type === 'seek') this.events.onSeek?.(msg.frame);
     });
     this.panel.onDidChangeViewState(e => this.events.onVisible(e.webviewPanel.visible));
     this.panel.onDidDispose(() => this.events.onDispose());
@@ -102,11 +105,19 @@ function getHtml(controlsVisible: boolean) {
   #show { position: absolute; right: 6px; bottom: 4px; display: none; cursor: pointer; font: 11px var(--vscode-font-family);
           color: #ccc; background: rgba(0,0,0,0.5); border: 0; border-radius: 3px; padding: 2px 6px; }
   body.hascontrols:not(.controls) #show { display: block; }
+  /* the timeline: shown while stopped, to scrub through the recording */
+  #timeline { position: absolute; left: 0; right: 0; display: none; align-items: center; gap: 8px;
+              padding: 2px 8px; box-sizing: border-box; background: rgba(0,0,0,0.7);
+              font: 11px var(--vscode-font-family); color: #ccc; }
+  body.stopped.haslog #timeline { display: flex; }
+  #scrub { flex: 1; accent-color: var(--vscode-focusBorder); }
+  #when { white-space: nowrap; font-variant-numeric: tabular-nums; }
 </style>
 </head>
 <body class="${controlsVisible ? 'controls' : ''}">
 <div id="wrap"><canvas id="screen" tabindex="0" width="1" height="1"></canvas></div>
 <div id="status"></div>
+<div id="timeline"><input id="scrub" type="range" min="0" max="0" value="0" title="Recorded frames: drag to go back in time"><span id="when"></span></div>
 <div id="bar"><span id="hints"></span><button id="hide" title="Hide controls">&times;</button></div>
 <button id="show" title="Show controls">Controls</button>
 <script nonce="${nonce}">
@@ -223,6 +234,31 @@ function getHtml(controlsVisible: boolean) {
     fit();
   }
 
+  // the timeline: where the shown frame is in the recording. Dragging asks
+  // the host to seek, one request at a time; the next frame answers it.
+  const timelineEl = document.getElementById('timeline');
+  const scrub = document.getElementById('scrub');
+  const whenEl = document.getElementById('when');
+  let seekPending = false, seekWanted = null;
+  function showTimeline(t) {
+    document.body.classList.toggle('haslog', !!t);
+    if (!t) return;
+    scrub.min = t.first;
+    scrub.max = t.last;
+    if (!seekPending && seekWanted == null) scrub.value = t.now.frame;
+    whenEl.textContent = 'frame ' + t.now.frame + (t.now.step ? ':' + t.now.step : '') + ' / ' + t.last;
+  }
+  function requestSeek(frame) {
+    if (seekPending) { seekWanted = frame; return; }
+    seekPending = true;
+    vscode.postMessage({ type: 'seek', frame });
+  }
+  function seekDone() {
+    seekPending = false;
+    if (seekWanted != null) { const f = seekWanted; seekWanted = null; requestSeek(f); }
+  }
+  scrub.addEventListener('input', () => requestSeek(Number(scrub.value)));
+
   // scale the canvas to fill the panel, keeping its aspect ratio
   function fit() {
     const { w, h, rotate, aspect } = layout;
@@ -231,6 +267,7 @@ function getHtml(controlsVisible: boolean) {
     let ratio = aspect || w / h;
     if (sideways) ratio = 1 / ratio;
     const barH = document.body.classList.contains('controls') ? bar.offsetHeight : 0;
+    timelineEl.style.bottom = barH + 'px';
     document.getElementById('wrap').style.bottom = barH + 'px';
     const W = window.innerWidth, H = window.innerHeight - barH;
     let dw = W, dh = W / ratio;
@@ -257,6 +294,8 @@ function getHtml(controlsVisible: boolean) {
       image.data.set(msg.pixels);
       ctx.putImageData(image, 0, 0);
       vscode.postMessage({ type: 'frameDone' });
+      if (msg.timeline) showTimeline(msg.timeline);
+      seekDone();
     } else if (msg.type === 'status') {
       const s = msg.status;
       if (s && JSON.stringify(s.controls) !== lastControls) {
@@ -264,6 +303,9 @@ function getHtml(controlsVisible: boolean) {
         showControls(s.controls);
       }
       statusEl.textContent = !s ? '' : s.state == 'running' ? '' : s.state == 'halted' ? 'Halted: ' + (s.message || '') : 'Paused';
+      document.body.classList.toggle('stopped', !!s && s.state != 'running');
+      showTimeline(s && s.timeline);
+      seekDone();  // a seek always ends with a status, even if its frame was dropped
     } else if (msg.type === 'audio') {
       onAudio(msg);
     } else if (msg.type === 'audioReset') {
diff --git a/extension/src/extension.ts b/extension/src/extension.ts
index b0a34909..6a676eb0 100644
--- a/extension/src/extension.ts
+++ b/extension/src/extension.ts
@@ -11,6 +11,8 @@ import type { BuildArgs } from './buildworker';
 import type { AudioChunk, EmuStatus } from './emuworker';
 import { WorkerHandle } from './engine';
 import { EmulatorPanel } from './emulatorpanel';
+import { WorkerDebugBackend } from './debugbackend';
+import { EmuDebugSession, LaunchArgs } from '../../src/tools/dapsession';
 import { Project, findRootDir, isHeaderFile, isInside, isOwnExtension, isSourceFile } from './projectinfo';
 import { CONFIG, ProjectScope } from './projectscope';
 import { BuildReason, BuildScheduler } from './autobuild';
@@ -54,6 +56,8 @@ let autoTarget: Target | undefined;
 let heldDiagnostics: { timer: NodeJS.Timeout, show: () => void } | undefined;
 /** Sound is muted; remembered across runs and webviews. */
 let muted = false;
+/** The debug session driving the emulator, if one is. */
+let debugging: { session: vscode.DebugSession, backend: WorkerDebugBackend } | undefined;
 
 export function activate(ctx: vscode.ExtensionContext) {
   context = ctx;
@@ -102,13 +106,24 @@ export function activate(ctx: vscode.ExtensionContext) {
   muted = ctx.globalState.get<boolean>('muted', false);
   vscode.commands.executeCommand('setContext', '8bitworkshop.muted', muted);
 
-  // F5 on an 8bitworkshop launch configuration runs it (no debugger yet)
+  // F5 on an 8bitworkshop launch configuration debugs it; Ctrl+F5 (Run
+  // Without Debugging) just runs it in the emulator panel
   ctx.subscriptions.push(vscode.debug.registerDebugConfigurationProvider('8bitworkshop', {
     resolveDebugConfiguration: async (folder, config) => {
-      await runLaunchConfiguration(folder, config);
-      return undefined;  // no debug session; the emulator panel runs it
+      if (config.noDebug) {
+        await runLaunchConfiguration(folder, config);
+        return undefined;  // no debug session; the emulator panel runs it
+      }
+      // F5 with no launch.json: debug the current target
+      return { type: '8bitworkshop', request: 'launch', name: 'Debug', ...config };
     },
   }));
+  ctx.subscriptions.push(vscode.debug.registerDebugAdapterDescriptorFactory('8bitworkshop', {
+    createDebugAdapterDescriptor: session => new vscode.DebugAdapterInlineImplementation(newDebugSession(session)),
+  }));
+  ctx.subscriptions.push(vscode.debug.onDidTerminateDebugSession(session => {
+    if (debugging?.session === session) debugging = undefined;
+  }));
 
   ctx.subscriptions.push(
     vscode.workspace.onDidSaveTextDocument(doc => onSave(doc)),
@@ -229,6 +244,7 @@ async function getEmu(platform: string): Promise<WorkerHandle> {
     emu.on('frame', frame => panel?.showFrame(frame));
     emu.on('audio', (chunk: AudioChunk) => panel?.showAudio(chunk));
     emu.on('audioReset', () => panel?.resetAudio());
+    emu.on('stopped', e => debugging?.backend.handleStop(e));
     emu.on('status', (s: EmuStatus | null) => {
       emuStatus = s;
       panel?.showStatus(s);
@@ -425,7 +441,10 @@ async function followActiveEditor() {
   await scope.setTargetChoice(project, 'follow');
 }
 
-async function startEmulator(target: Target, build: BuildOutcome) {
+/** Start `build` in the emulator panel. Returns false if it didn't start. */
+async function startEmulator(target: Target, build: BuildOutcome, opts: { paused?: boolean } = {}): Promise<boolean> {
+  // a plain Run replaces what the debugger was looking at
+  if (debugging && !opts.paused) vscode.debug.stopDebugging(debugging.session);
   // each run gets a fresh worker: platforms keep global state (see emuworker)
   emu?.dispose();
   emu = undefined;
@@ -437,7 +456,10 @@ async function startEmulator(target: Target, build: BuildOutcome) {
       onControlsVisible: visible => context.globalState.update('controlsVisible', visible),
       // don't burn CPU on a hidden screen
       onVisible: visible => { emu?.call('setVisible', visible); },
+      onSeek: frame => { emu?.call('seekFrame', frame); },
       onDispose: () => {
+        // closing the emulator ends the program, and any session debugging it
+        if (debugging) vscode.debug.stopDebugging(debugging.session);
         panel = undefined;
         emuStatus = null;
         running = undefined;
@@ -454,15 +476,17 @@ async function startEmulator(target: Target, build: BuildOutcome) {
   panel.setTitle(`${title} (${target.platform})`);
   panel.setMuted(muted);
   try {
-    emuStatus = await worker.call<EmuStatus>('start', target.platform, build.output, build.files);
+    emuStatus = await worker.call<EmuStatus>('start', target.platform, build.output, build.files, opts);
     worker.call('setMuted', muted);
     panel.showStatus(emuStatus);
     running = target;
     runningBuild = build;
     output.appendLine(`Running ${title} on ${target.platform}`);
+    return true;
   } catch (e) {
     output.appendLine(`Emulator failed to start: ${e && e.stack || e}`);
     output.show(true);
+    return false;
   }
 }
 
@@ -470,6 +494,8 @@ async function startEmulator(target: Target, build: BuildOutcome) {
 async function reloadEmulator(target: Target, reason: BuildReason, result: BuildOutcome) {
   if (!panel || !emuStatus || !running || !result.output) return;
   if (running.main.toString() !== target.main.toString()) return;
+  // the code under the debugger doesn't change beneath it; F5 again rebuilds
+  if (debugging) return;
   var mode = config(target.main).get<string>('reloadOnBuild', 'always');
   if (mode === 'never' || (mode === 'onSave' && reason === 'type')) return;
   if (emuStatus.platform !== target.platform) {
@@ -1102,18 +1128,65 @@ async function addLaunchConfiguration() {
 }
 
 async function runLaunchConfiguration(folder: vscode.WorkspaceFolder | undefined, cfg: vscode.DebugConfiguration) {
+  if (!cfg.mainFile) {
+    // Ctrl+F5 with no launch.json: run the current target
+    return buildCommand(true);
+  }
+  var target = await launchTarget(folder, cfg);
+  await buildAndMaybeRun(target, true, 'command');
+}
+
+/** What a launch configuration runs: its mainFile, or the current target. */
+async function launchTarget(folder: vscode.WorkspaceFolder | undefined, cfg: { name?: string, mainFile?: string, platform?: string, tool?: string }): Promise<Target> {
   var base = folder?.uri.fsPath || vscode.workspace.workspaceFolders?.[0]?.uri.fsPath;
   if (!cfg.mainFile || !base) {
-    // F5 with no launch.json: run the current target
-    return buildCommand(true);
+    var current = currentTarget();
+    if (!current) throw new Error('open a program to debug, or set mainFile in the launch configuration');
+    return current;
   }
   var file = path.resolve(base, cfg.mainFile);
   var project = scope.projectFor(vscode.Uri.file(file));
   var platform = cfg.platform || project?.platform;
-  if (!platform) {
-    vscode.window.showErrorMessage(`8bitworkshop: launch configuration "${cfg.name}" needs a platform.`);
-    return;
-  }
+  if (!platform) throw new Error(`launch configuration "${cfg.name}" needs a platform`);
   if (project) await scope.setTargetChoice(project, file);
-  await buildAndMaybeRun({ platform, main: vscode.Uri.file(file), tool: cfg.tool, project }, true, 'command');
+  return { platform, main: vscode.Uri.file(file), tool: cfg.tool, project };
+}
+
+/**
+ * A debug session over the emulator worker. The adapter (shared with
+ * `8bws dap`) runs here in the extension host; the debugger itself runs in
+ * the worker, next to the emulator.
+ */
+function newDebugSession(session: vscode.DebugSession): EmuDebugSession {
+  // the worker this session launched; a later Run starts another
+  var worker: WorkerHandle | undefined;
+  var backend = new WorkerDebugBackend(
+    (method, ...args) => {
+      if (!worker || worker !== emu) throw new Error('the emulator this session started has stopped');
+      return worker.call('debug', method, ...args);
+    },
+    async args => {
+      var r = await launchForDebug(session.workspaceFolder, args);
+      worker = emu;
+      return r;
+    },
+    async () => {
+      if (debugging?.session === session) debugging = undefined;
+      // stopping the session stops its program, not one started since
+      if (worker && worker === emu) panel?.dispose();
+    });
+  debugging = { session, backend };
+  return new EmuDebugSession(backend);
+}
+
+/** Build the program and load it stopped, with its listings for the debugger. */
+async function launchForDebug(folder: vscode.WorkspaceFolder | undefined, args: LaunchArgs): Promise<{ root: string }> {
+  var target = await launchTarget(folder, args);
+  var result = await runBuild(target, 'command');
+  if (!result || !result.success) throw new Error('the build failed; see Problems');
+  if (!result.output) throw new Error('the build produced no ROM to run');
+  if (!await startEmulator(target, result, { paused: true })) throw new Error('the emulator failed to start; see Output');
+  var mainPath = path.posix.basename(target.main.path);
+  await emu!.call('debug', 'setBuild', { listings: result.listings, symbols: result.symbolmap, mainPath, paths: result.paths });
+  return { root: path.dirname(target.main.fsPath) };
 }
diff --git a/extension/test/emuworker.test.ts b/extension/test/emuworker.test.ts
index adea5730..4880e4ae 100644
--- a/extension/test/emuworker.test.ts
+++ b/extension/test/emuworker.test.ts
@@ -7,6 +7,9 @@ import { Rpc } from '../src/rpc';
 import { findRootDir } from '../src/projectinfo';
 import { Builder, ProjectFileProvider } from '../src/buildcore';
 import type { AudioChunk, EmuStatus, FrameEvent } from '../src/emuworker';
+import { WorkerDebugBackend } from '../src/debugbackend';
+import { EmuDebugSession } from '../../src/tools/dapsession';
+import { DapClient } from '../../test/unit/dapclient';
 
 // Drives out/emuworker.js in a worker thread, the way the extension host does.
 // Mocha runs from extension/, so BIOS fetches must resolve against ROOT.
@@ -230,6 +233,33 @@ describe('extension emuworker', function () {
       assert.equal(statuses[statuses.length - 1].state, 'paused');
     });
 
+    it('drives the debug adapter through the worker, as the extension does', async function () {
+      var backend = new WorkerDebugBackend((method, ...args) => rpc.call('debug', method, ...args), async () => {
+        await rpc.call('start', 'mw8080bw', built.output, built.files, { paused: true });
+        await rpc.call('debug', 'setBuild', { listings: built.listings, symbols: built.symbolmap, mainPath: 'game2.c', paths: built.paths });
+        return { root: '/proj' };
+      }, async () => { });
+      rpc.on('stopped', e => backend.handleStop(e));
+      var c = new DapClient(new EmuDebugSession(backend));
+      await c.request('initialize', { adapterID: '8bitworkshop', pathFormat: 'path', linesStartAt1: true, columnsStartAt1: true });
+      await c.request('launch', { mainFile: 'game2.c' });
+      await c.event('initialized');
+      var { breakpoints } = await c.request('setBreakpoints', { source: { path: '/proj/game2.c' }, breakpoints: [{ line: 166 }] });
+      assert.ok(breakpoints[0].verified);
+      await c.request('configurationDone');
+      assert.equal((await c.event('stopped')).reason, 'breakpoint');
+      var frame = await c.where();
+      assert.equal(frame.source.path, '/proj/game2.c');
+      assert.equal(frame.line, 166);
+      await c.request('next', { threadId: 1 });
+      await c.event('stopped');
+      assert.equal((await c.where()).line, 167);
+      await c.request('stepBack', { threadId: 1 });
+      await c.event('stopped');
+      assert.equal((await c.where()).line, 166);
+      assert.match((await c.request('evaluate', { expression: 'now', context: 'repl' })).result, /past/);
+    });
+
     it('pauses with a stop, and seeks to a recorded frame', async function () {
       await rpc.call('start', 'mw8080bw', built.output, built.files);
       await waitForFrames(10);
diff --git a/test/unit/dapclient.ts b/test/unit/dapclient.ts
new file mode 100644
index 00000000..f4d89689
--- /dev/null
+++ b/test/unit/dapclient.ts
@@ -0,0 +1,43 @@
+// A test client for the debug adapter, shared by the root and extension tests.
+
+import { DebugProtocol } from "@vscode/debugprotocol";
+import type { EmuDebugSession } from "../../src/tools/dapsession";
+
+/** Just enough of a DAP client: requests by sequence number, events by name. */
+export class DapClient {
+  private seq = 1;
+  private pending = new Map<number, (r: DebugProtocol.Response) => void>();
+  private events: DebugProtocol.Event[] = [];
+  private waiting: { name: string, resolve: (e: DebugProtocol.Event) => void }[] = [];
+
+  constructor(readonly session: EmuDebugSession) {
+    session.onDidSendMessage((m: any) => {
+      if (m.type === 'response') this.pending.get(m.request_seq)?.(m);
+      else if (m.type === 'event') {
+        const w = this.waiting.findIndex(w => w.name === m.event);
+        if (w >= 0) this.waiting.splice(w, 1)[0].resolve(m);
+        else this.events.push(m);
+      }
+    });
+  }
+
+  request(command: string, args: any = {}): Promise<any> {
+    const seq = this.seq++;
+    return new Promise((resolve, reject) => {
+      this.pending.set(seq, (r) => r.success ? resolve(r.body) : reject(new Error(r.message)));
+      this.session.handleMessage({ seq, type: 'request', command, arguments: args } as any);
+    });
+  }
+
+  /** The next event of this name, including one that already came. */
+  event(name: string): Promise<any> {
+    const i = this.events.findIndex(e => e.event === name);
+    if (i >= 0) return Promise.resolve(this.events.splice(i, 1)[0].body);
+    return new Promise(resolve => this.waiting.push({ name, resolve: e => resolve(e.body) }));
+  }
+
+  async where() {
+    const { stackFrames } = await this.request('stackTrace', { threadId: 1 });
+    return stackFrames[0];
+  }
+}
diff --git a/test/unit/testdapsession.ts b/test/unit/testdapsession.ts
index 23a6c00c..cf7f0c9a 100644
--- a/test/unit/testdapsession.ts
+++ b/test/unit/testdapsession.ts
@@ -1,7 +1,7 @@
 import assert from "assert";
 import { before, describe, it } from "mocha";
-import { DebugProtocol } from "@vscode/debugprotocol";
 import { EmuDebugSession } from "../../src/tools/dapsession";
+import { DapClient } from "./dapclient";
 import { LocalDebugBackend } from "../../src/tools/daplocal";
 import { loadPlatform } from "../../src/tools/emutarget";
 import { compileSourceFile, preload } from "../../src/tools/testlib";
@@ -12,53 +12,14 @@ import { compileSourceFile, preload } from "../../src/tools/testlib";
 const ROOT = '/proj';
 let build: any;
 
-/** Just enough of a DAP client: requests by sequence number, events by name. */
-class Client {
-  private seq = 1;
-  private pending = new Map<number, (r: DebugProtocol.Response) => void>();
-  private events: DebugProtocol.Event[] = [];
-  private waiting: { name: string, resolve: (e: DebugProtocol.Event) => void }[] = [];
-
-  constructor(readonly session: EmuDebugSession) {
-    session.onDidSendMessage((m: any) => {
-      if (m.type === 'response') this.pending.get(m.request_seq)?.(m);
-      else if (m.type === 'event') {
-        const w = this.waiting.findIndex(w => w.name === m.event);
-        if (w >= 0) this.waiting.splice(w, 1)[0].resolve(m);
-        else this.events.push(m);
-      }
-    });
-  }
-
-  request(command: string, args: any = {}): Promise<any> {
-    const seq = this.seq++;
-    return new Promise((resolve, reject) => {
-      this.pending.set(seq, (r) => r.success ? resolve(r.body) : reject(new Error(r.message)));
-      this.session.handleMessage({ seq, type: 'request', command, arguments: args } as any);
-    });
-  }
-
-  /** The next event of this name, including one that already came. */
-  event(name: string): Promise<any> {
-    const i = this.events.findIndex(e => e.event === name);
-    if (i >= 0) return Promise.resolve(this.events.splice(i, 1)[0].body);
-    return new Promise(resolve => this.waiting.push({ name, resolve: e => resolve(e.body) }));
-  }
-
-  async where() {
-    const { stackFrames } = await this.request('stackTrace', { threadId: 1 });
-    return stackFrames[0];
-  }
-}
-
-async function launch(): Promise<Client> {
+async function launch(): Promise<DapClient> {
   const backend = new LocalDebugBackend(async () => {
     const target = await loadPlatform('mw8080bw');
     await target.start();
     await target.loadROM(build.output);
     return { target, root: ROOT, debugInfo: { listings: build.listings, symbols: build.symbolmap, mainPath: 'game2.c' } };
   });
-  const c = new Client(new EmuDebugSession(backend));
+  const c = new DapClient(new EmuDebugSession(backend));
   const caps = await c.request('initialize', { adapterID: '8bitworkshop', linesStartAt1: true, columnsStartAt1: true, pathFormat: 'path' });
   assert.ok(caps.supportsDisassembleRequest);
   await c.request('launch', { program: 'game2.c' });