Code OSS Dev - Launch + Debug

You're working on VS Code itself and you want to:

1. Launch a Code OSS build from sources that is already signed in (Copilot, GitHub, etc.) so chat / agent flows work end-to-end.
2. Drive it with @playwright/cli over CDP (UI automation).
3. Optionally attach a debugger via dap-cli to set breakpoints in the renderer, extension host, or main process.
4. Run multiple instances at once without port conflicts.

This skill provides a launcher that clones an authenticated user-data-dir to a throwaway temp folder, picks free ports for every debug surface, and prints them as JSON so you can pick them up programmatically.

The clone is slim: workspace storage, browser caches, file history, cached VSIX backups, and old logs are excluded by default. Auth tokens themselves live in the OS keychain (shared automatically) plus small files inside User/globalStorage - both of which are preserved.

Prerequisites

• macOS or Linux. The launcher is a bash script and depends on rsync, curl, nohup, and Node on PATH. The example caller snippets below also use jq (parse the JSON output) and lsof (kill-by-port fallback) — install those if you plan to use them, but the launcher itself does not require them.
• A VS Code checkout with node_modules/ installed (npm install if missing — do not symlink from a sibling worktree; that breaks builds in subtle ways).
• A VS Code checkout with sources built. Run npm run compile once (one-shot) or npm run watch for incremental rebuilds. Both build the full client and all built-in extensions under extensions/. You must build the full product to run successfully, building just the client is not enough.
• An authenticated Code OSS profile to seed from. By default the launcher uses ~/.vscode-oss-dev, which is the user-data-dir the repo's launch.json configs use - if the user has ever signed in to Copilot in a dev build, this should work. Only pass --source-user-data-dir <path> (or set $CODE_OSS_DEV_AUTHED_USER_DATA_DIR) when you specifically want to seed from a different profile (e.g. your regular ~/Library/Application Support/Code install).
  • If Code OSS launches and needs a sign-in, don't give up! Use the questions tool to ask the user to sign in.
• @playwright/cli available (it's a devDependency in the vscode repo - npm install then use npx @playwright/cli).
• For debugger work: dap-cli on PATH. If debugger support would be useful but the dap-cli skill is not present, prompt the user to install it from https://github.com/roblourens/dap-cli.
• CSS selectors are internal implementation details. If a selector-based eval stops working, take a fresh snapshot, inspect the current DOM, and update the selector rather than assuming an old one still applies.

The launcher copies the source profile to a temp dir and never mutates the original. Each launch gets its own isolated --user-data-dir and --extensions-dir.

The launcher always sets files.simpleDialog.enable: true in the launched profile's User/settings.json. This is required for automation: VS Code's native OS file dialogs cannot be driven via @playwright/cli over CDP and are completely unreachable over SSH on headless macOS. The simple (quick-input) dialog can be navigated with press and clipboard paste. The override is per-launch and only affects throwaway profiles.

Launch

The launcher script lives next to this SKILL.md at scripts/launch.sh. Resolve it relative to wherever this skill file is installed - do not hardcode an absolute path.

# LAUNCH=<dir-of-this-SKILL.md>/scripts/launch.sh
"$LAUNCH"                                    # default: workbench
"$LAUNCH" --agents                           # Agents window
"$LAUNCH" -- <workspace-path>                # forward extra args to code.sh
"$LAUNCH" --source-user-data-dir <path>      # pick a specific authed profile
"$LAUNCH" --repo <vscode-repo-root>          # if not run from the repo
"$LAUNCH" --clone-extensions                 # start with a copy of the source extensions/ (~few seconds)
"$LAUNCH" --full                             # skip slim excludes; copy everything

What gets copied (slim mode, the default)

The exclude list mirrors the one used by VS Code's own perf-test skill (.github/skills/auto-perf-optimize), which is known to keep Copilot auth and language-model availability working. Specifically WebStorage/, Service Worker/, Local Storage/, Cookies, Network Persistent State, TransportSecurity, Trust Tokens, Preferences, machineid, and the entire User/globalStorage/ (which holds state.vscdb - where extension SecretStorage blobs live, encrypted with the OS keychain key) are all preserved. Auth tokens themselves stay in the OS keychain, which is per-user, so they follow automatically.

Excluded (transient, regenerable, or known-not-needed):

• User/workspaceStorage/ - per-workspace state, including stored chat sessions (often multi-GB)
• User/History/ - local file edit history
• CachedExtensionVSIXs - backup VSIXs (hundreds of MB)
• logs
• Chromium caches: Cache, Code Cache, CachedData, GPUCache, ShaderCache, Dawn*Cache, component_crx_cache
• Backups, blob_storage, BrowserMetrics, Crashpad, Session Storage
• Singleton*, *.lock, *.sock (would conflict with the source instance)

extensions/ defaults to a fresh empty directory - fastest and conflict-free, but the launched instance starts with no third-party extensions installed. Pass --clone-extensions to copy the source extensions dir into the temp profile so the new instance is independent of the source. Pass --full to skip all excludes if you suspect the slim copy is missing something you need.

Why never share the source extensions/ dir directly? The extension management service writes a shared .obsolete file; two concurrent writers crash each other's shared background process. The launcher always uses an isolated extensions dir for the same reason it uses --shared-data-dir (see below).

If the launched window says "language model unavailable" or otherwise looks unauthed, ask the user to sign in.

The script runs pre-launch (electron download, compile-if-missing, built-in extensions) in the foreground, then starts Code OSS detached and blocks until the renderer's CDP endpoint is responding (up to ~90s) before printing the JSON line on stdout. If anything fails — preLaunch errors, code.sh exits early, CDP never opens — the script exits non-zero and dumps the relevant log tail to stderr.

{"pid":12345,"cdpPort":53111,"extHostPort":53112,"mainPort":53113,"agentHostPort":53114,"userDataDir":".../user-data","extensionsDir":".../extensions","sharedDataDir":".../shared-data","runDir":"...","logFile":".../code.log","repo":"...","agents":false}

Capture it with jq — no retry loop needed, CDP is already up when the JSON is printed:

INFO=$("$LAUNCH" | tail -n1)
CDP=$(jq -r .cdpPort        <<<"$INFO")
EXT=$(jq -r .extHostPort    <<<"$INFO")
MAIN=$(jq -r .mainPort      <<<"$INFO")
AGENT=$(jq -r .agentHostPort <<<"$INFO")
LOG=$(jq -r .logFile        <<<"$INFO")
PID=$(jq -r .pid            <<<"$INFO")

What each port is for

Drive the UI with @playwright/cli

Use the dynamic cdpPort from the launch JSON. The normal loop is: attach, confirm the target, snapshot, interact, then re-snapshot after meaningful UI changes.

Always pick a unique PW_SESSION name and pass it as -s=$PW_SESSION on every npx @playwright/cli ... call. The CLI is backed by a persistent daemon (cliDaemon.js) keyed by session name; if two shells both omit -s=, they share the implicit "default" session and the most-recently-attached CDP "wins" for every subsequent command from either shell. The launch skill is built around isolation (per-instance UDD, ports, shared-data-dir), and this pattern keeps that isolation intact at the Playwright-driving layer too. A note on the alternative PLAYWRIGHT_CLI_SESSION env var: it's documented in the package README and works correctly for open-style workflows, but it interacts poorly with attach --cdp=... (the daemon ends up with both --cdp=... and --endpoint=<env-value>, and the latter wins, causing a connect ENOENT failure). Confirmed against @playwright/cli@0.1.13. Explicit -s=NAME works in all modes.

# At the top of your script / subagent prompt:
PW_SESSION="my-uniq-$$"        # any unique string; $$ is fine for one shell per agent

# launch.sh blocks until CDP is ready, so a single attach is enough.
npx @playwright/cli -s=$PW_SESSION attach --cdp=http://127.0.0.1:$CDP
npx @playwright/cli -s=$PW_SESSION tab-list
npx @playwright/cli -s=$PW_SESSION snapshot

After attach, later @playwright/cli commands keep using the connected app until you close or reattach — as long as you keep passing the same -s=$PW_SESSION.

Selecting the right Electron target

Electron apps can expose multiple windows or webviews. If tab-list shows about:blank, a webview, or otherwise the wrong target, switch targets before interacting:

npx @playwright/cli -s=$PW_SESSION tab-list
npx @playwright/cli -s=$PW_SESSION tab-select 2
npx @playwright/cli -s=$PW_SESSION snapshot

If a target looks stale after relaunching, run npx @playwright/cli -s=$PW_SESSION close, attach again with $CDP, and re-check tab-list.

Focusing the chat input (works on Code OSS, including the Agents window)

# macOS
npx @playwright/cli -s=$PW_SESSION press Control+Meta+i
# Linux / Windows
npx @playwright/cli -s=$PW_SESSION press Control+Alt+i

Typing into Monaco (chat input, editors)

fill and type silently fail on Code OSS — Monaco's native-edit-context element doesn't react to Playwright's default input pipeline. Use one of these alternatives:

• scripts/monaco-paste.sh helper (recommended — fast, no system clipboard, parallel-safe). Reads text from a positional arg or stdin and dispatches a ClipboardEvent('paste') with a DataTransfer payload into the focused chat-input Monaco editor. Honors --session NAME or $PW_SESSION env so it stays inside the same -s= session as everything else.

  LAUNCH_DIR=<dir-of-this-SKILL.md>           # the same dir that holds scripts/launch.sh
  PASTE="$LAUNCH_DIR/scripts/monaco-paste.sh"
  export PW_SESSION                            # helper reads this env var
  
  # Send a prompt:
  npx @playwright/cli -s=$PW_SESSION press Control+Meta+i  # focus chat input
  "$PASTE" 'Please run `pwd && ls` using your terminal tool.'
  npx @playwright/cli -s=$PW_SESSION press Enter
  
  # Long / arbitrary text via stdin (avoids any shell-quoting headaches):
  printf 'multi-line prompt\nwith backticks `x`\nand emoji 🎉' | "$PASTE"
  
  # Append without clearing:
  "$PASTE" --append " continued text"
  
  # Skip the read-back check (useful when intentionally pasting more than the
  # chat input's ~600-character soft cap):
  "$PASTE" --no-verify "...long text..."
  
  # Or pass the session explicitly per call (if you don't want to export PW_SESSION):
  "$PASTE" --session "$PW_SESSION" "..."

  The helper prints a single JSON line on stdout: {ok, actualLength, expectedLength, viewLineCount, firstViewLine, error?}. Exit 0 on success, 1 on verify failure, 2 on argument errors. Tested reliable across 20+ sequential pastes including unicode (中文), emoji (🎉), backticks, ampersands, embedded quotes, and newlines.

  Why a helper script and not just docs: the inline recipe involves a multi-line node -e heredoc with embedded JS template literals, which is exactly the kind of code that gets miscopied. There are also three non-obvious correctness traps the helper handles internally:

  1. Monaco's native-edit-context doesn't react to fill or type, only to actual paste events (or per-key press).
  2. Monaco renders ASCII spaces as U+00A0 (NBSP) in the view-line DOM, so verification has to normalize before comparing.
  3. Monaco updates its DOM asynchronously after a paste event — a synchronous read-back inside the same eval returns stale state. The helper waits two requestAnimationFrame ticks before reading.
• Per-key press (universal but slow — each press is a separate CLI invocation with Node startup cost):

  npx @playwright/cli -s=$PW_SESSION press H
  npx @playwright/cli -s=$PW_SESSION press i
  npx @playwright/cli -s=$PW_SESSION press Enter

• Clipboard paste via pbcopy (fast on macOS, but NSPasteboard is system-wide so any concurrent shell that touches the pasteboard will collide). Only use when nothing else on the machine is using the clipboard for the duration of the paste.

  printf '%s' "Your prompt here" | pbcopy
  npx @playwright/cli -s=$PW_SESSION press Control+Meta+i
  npx @playwright/cli -s=$PW_SESSION press Meta+v
  npx @playwright/cli -s=$PW_SESSION press Enter

The focus shortcut should leave document.activeElement on VS Code's native-edit-context editing surface. That is a useful sanity check when key presses appear to do nothing.

Parallel multi-instance pattern

Because the launch skill is built around isolation, the natural workload is many agents on one machine, each driving their own Code OSS. The pattern boils down to giving each agent a unique PW_SESSION and passing it everywhere:

# In agent A's shell:
PW_SESSION="agent-A-$$"
INFO=$("$LAUNCH" --agents -- --use-mock-keychain | tail -n1)
CDP=$(jq -r .cdpPort <<<"$INFO")
npx @playwright/cli -s=$PW_SESSION attach --cdp=http://127.0.0.1:$CDP
"$PASTE" "prompt for A"   # helper picks up $PW_SESSION

# In agent B's shell (running concurrently):
PW_SESSION="agent-B-$$"
INFO=$("$LAUNCH" --agents -- --use-mock-keychain | tail -n1)
CDP=$(jq -r .cdpPort <<<"$INFO")
npx @playwright/cli -s=$PW_SESSION attach --cdp=http://127.0.0.1:$CDP
"$PASTE" "prompt for B"

Each agent gets its own cliDaemon bound to its own CDP, so the pastes / clicks / snapshots don't cross-contaminate. Verified live with two concurrent instances. macOS Mach-ports caveat: on macOS, beyond ~2–3 concurrent Code OSS instances Crashpad's exception handler tends to die with mach_port_request_notification: invalid capability. That's a separate, OS-level limit; it's not affected by the session name.

Cleanup for cliDaemon processes: stop your session's daemon with npx @playwright/cli -s=$PW_SESSION close, or nuke all stale daemons (after killing all the Code OSS windows) with npx @playwright/cli kill-all. Session daemons live under ~/Library/Caches/ms-playwright/daemon/<hash>/.

Agents window selector differences

The Agents window does not use the regular workbench .interactive-input-editor wrapper. Selector checks that are scoped to that wrapper may return nothing even when the Agents chat input is focused.

// Regular-workbench-specific selector; do not assume this exists in Agents.
document.querySelectorAll('.interactive-input-editor .view-line')

// More useful checks in Agents.
document.querySelectorAll('.view-line')
document.activeElement?.className === 'native-edit-context'

The Control+Meta+i / Control+Alt+i focus shortcut still works; only the DOM shape after focus differs.

Verifying and clearing chat text

For the regular workbench sidebar, this confirms that text landed in the Monaco input:

npx @playwright/cli -s=$PW_SESSION eval '
(() => {
  const sidebar = document.querySelector(".part.auxiliarybar");
  const viewLines = sidebar?.querySelectorAll(".interactive-input-editor .view-line") ?? [];
  return Array.from(viewLines).map(viewLine => viewLine.textContent).join("|");
})()'

For the Agents window, use a fresh snapshot plus the broader selector/focus checks above instead of assuming the regular sidebar wrapper is present.

To clear the focused Monaco input:

# macOS
npx @playwright/cli -s=$PW_SESSION press Meta+a
# Linux / Windows
npx @playwright/cli -s=$PW_SESSION press Control+a
npx @playwright/cli -s=$PW_SESSION press Backspace

If the keyboard shortcut cannot focus chat because the surface is not available yet, take a snapshot and navigate the UI into a state where chat exists before retrying. Avoid treating completed CLI commands as proof that text was entered.

Screenshots (paper trail)

SHOTS="$PWD/screenshots/$(date +%Y-%m-%dT%H-%M-%S)"
mkdir -p "$SHOTS"
npx @playwright/cli -s=$PW_SESSION screenshot --filename="$SHOTS/after-launch.png"

Keep screenshots inside the workspace, not /tmp, so they survive for review.

For wide windows, --full-page can make layout easier to inspect, and element screenshots are useful when a snapshot gives a stable ref for the panel you care about:

npx @playwright/cli -s=$PW_SESSION screenshot --full-page --filename="$SHOTS/full-window.png"
npx @playwright/cli -s=$PW_SESSION screenshot e42 --filename="$SHOTS/panel.png"

On macOS, a screenshot "Permission denied" failure usually means the terminal lacks Screen Recording permission. Use text/state verification while resolving that permission issue.

Debug with dap-cli

To set breakpoints in VS Code source while the window is running, attach dap-cli to one of the ports. If dap-cli would help but the corresponding skill is unavailable, prompt the user to install it from https://github.com/roblourens/dap-cli before continuing with debugger-specific steps.

Read the dap-cli skill for the full attach/breakpoint/inspect workflow when it is available - this skill only tells you which port to point it at:

• Extension host (most common - Copilot Chat extension, built-in extensions, your own extension under development) -> extHostPort
• Main process (Electron lifecycle, window/menu wiring, IPC) -> mainPort
• Local agent host (src/vs/platform/agentHost/node/..., agent session lifecycle, AHP wiring, Claude/Copilot agent providers) -> agentHostPort
• Renderer (the workbench itself, src/vs/workbench/...) -> cdpPort

You can run @playwright/cli and dap-cli against the same window simultaneously - drive the UI with one terminal, hit a breakpoint and inspect state in another.

Multiple instances

Every launch picks fresh ports and a fresh temp runDir, so you can run as many concurrent Code OSS windows as your machine can handle. Each one's ports come back in its own JSON blob - keep them separate.

The launcher also passes --shared-data-dir=<runDir>/shared-data. This is required for multi-instance isolation: Code OSS keeps a fixed-path SQLite DB at ~/.<dataFolderName>-shared/sharedStorage/state.vscdb that is not covered by --user-data-dir. Without overriding it, two concurrent instances would fight over the same file and one would die with "shared background process terminated unexpectedly". Each launch gets its own shared-data dir.

Restart after source changes

Workbench code is loaded when the Code OSS window starts; source changes are not hot-reloaded into an already-running instance. After the build output is current, kill the launched process, launch again, and reattach to the new cdpPort from the new JSON blob.

kill "$PID" 2>/dev/null || true
INFO=$("$LAUNCH" | tail -n1)
CDP=$(jq -r .cdpPort <<<"$INFO")
PID=$(jq -r .pid <<<"$INFO")
npx @playwright/cli -s=$PW_SESSION attach --cdp=http://127.0.0.1:$CDP
npx @playwright/cli -s=$PW_SESSION tab-list
npx @playwright/cli -s=$PW_SESSION snapshot

If you are iterating frequently, keep the repo build/watch task running separately so relaunches pick up already-generated output.

Cleanup

The launcher writes everything under a temp runDir (printed in the JSON). When you're done:

# Disconnect this session's playwright daemon (leaves other sessions' daemons alone)
npx @playwright/cli -s=$PW_SESSION close

# Or nuke any stale daemons left behind by crashed callers across all sessions:
# npx @playwright/cli kill-all

# Kill the Code OSS instance
kill "$PID" 2>/dev/null || true
# Or by port if you've lost the pid:
pids=$(lsof -t -i :$CDP); [ -n "$pids" ] && kill $pids

# Remove the throwaway profile
rm -rf "$(dirname "$LOG")"

Code OSS is a full Electron app and easily eats 1-4 GB. Always clean up.

Troubleshooting

• "Sent env to running instance. Terminating..." - The dynamic --user-data-dir should prevent this. If you see it, another Code OSS is using the same profile path; pass --source-user-data-dir to a different source or check that the temp copy actually happened (ls "$(jq -r .userDataDir <<<"$INFO")").
• Renderer ESM errors / import { Menu } from 'electron' - ELECTRON_RUN_AS_NODE is set in your env. The launcher unsets it for the child, but if you spawn code.sh yourself, do the same.
• Built-in extension fails to load (Cannot find module .../extensions/.../out/extension.js) - extensions weren't compiled. Run npm run compile (one-shot, also rebuilds all built-in extensions) or npm run watch (incremental). A common cause: you ran npm run transpile-client to satisfy unit tests, which populated out/ but not extensions/*/out/, so preLaunch's "is out/ missing?" check skipped the compile.
• launch.sh exits non-zero with a log tail - either pre-launch failed, code.sh died before CDP came up, or CDP never opened within 90s. The tail printed to stderr is from runDir/code.log - read it to diagnose.
• Snapshot shows the wrong page or no expected controls - use tab-list, switch with tab-select <index> if needed, then re-snapshot before interacting.
• CLI typing commands complete but the input stays empty - focus chat with the platform shortcut, use press or clipboard paste rather than fill / type, then verify the input state before sending.
• Auth missing in the launched window - confirm the source profile is actually authed (ls "$SOURCE_UDD" should contain User/, and ls "$SOURCE_UDD/User/globalStorage" should show persisted extension state). Some auth lives in the OS keychain - that's per-user, so it follows automatically as long as you're running as the same user.