debug-ui

name	debug-ui
description	Drive and visually QA the dev-3.0 UI in a real browser (headless Chromium via agent-browser). Use when verifying a UI/UX change, reproducing a visual bug, taking screenshots of the running app, or self-QA before review. Triggers — "check the UI", "screenshot the app", "does this render", "QA this screen", "verify the UI change in a browser", "drive the app".

debug-ui — QA the dev-3.0 UI in a real browser

See and drive the running dev-3.0 UI in headless Chromium — click, type, screenshot, read console errors — instead of guessing whether a UI change works. No desktop/native dependency; it works the same in a plain terminal session.

This is dev-internal tooling for the dev-3.0 repo — NOT one of the skills dev3 ships to its users (those live in src/bun/agent-skills.ts).

The whole flow

This task's dev-server is the web UI: bun run dev serves the full app in local remote mode at a stable per-machine token and a CLI-derivable port — no separate dev3 remote. The loop is always the same four beats: values → server → browser → clean up.

# 1. Values. AGENT_BROWSER_SESSION isolates THIS task's browser from every other agent's —
#    without it all agents share one global "default" session and stomp each other (see
#    Gotchas). Derived from the always-present $DEV3_TASK_ID, so this exact line is
#    copy-paste-safe at the top of ANY block that calls agent-browser.
export AGENT_BROWSER_SESSION="dev3-${DEV3_TASK_ID%%-*}"
CODE=$(cat "$HOME/.dev3.0/dev-web-access-code" 2>/dev/null || bun scripts/dev-web-code.ts)
PORT=${DEV3_PORT0:-$(dev3 dev-server status | grep -oE 'DEV3_PORT0=[0-9]+' | cut -d= -f2)}

# 2. Start a FRESH dev-server and wait for it to come up. (Skip the start only if one is
#    already running for THIS task — but see the build-snapshot gotcha: stale code needs a
#    restart, so when in doubt restart.)
dev3 dev-server start
until curl -sf "http://localhost:$PORT/?token=$CODE" >/dev/null; do sleep 2; done

# 3. Drive it. Every agent-browser call inherits AGENT_BROWSER_SESSION, so it all runs in
#    this task's own session. (Load /agent-browser for the full command set.) The screenshot
#    path is task-scoped too, so parallel agents never overwrite each other's PNG.
agent-browser set viewport 1440 900
agent-browser open "http://localhost:$PORT/?token=$CODE"
agent-browser wait --load networkidle
agent-browser screenshot "/tmp/dev3-ui-${DEV3_TASK_ID%%-*}.png"   # then Read it back to look
agent-browser errors                          # confirm no console errors

# 4. Always clean up what you started. `close` closes only THIS session's browser.
agent-browser close
dev3 dev-server stop          # the port frees a second or two later (graceful shutdown)

That's it. DEV3_REMOTE_PORT=${DEV3_PORT0:-0} is wired into the repo's dev script and portCount: 1 is committed in .dev3/config.json, so the dev app binds the exact port shown above (see decision 093).

Gotchas

• The browser is a machine-global singleton — isolate per task or agents stomp each other. Every agent-browser call with no session lands in one shared "default" session: one browser process, one global viewport. When two task agents QA at the same time they collide — agent B's open silently replaces agent A's page, so A's next screenshot captures B's UI. The fix is step 1: export AGENT_BROWSER_SESSION="dev3-${DEV3_TASK_ID%%-*}" gives each task its own isolated session/profile (verify with agent-browser session / session list), and agent-browser close then closes only your session. The Bash tool reinitializes the shell per call, so an export does not carry across separate invocations — the line derives from the always-present $DEV3_TASK_ID, so just repeat it at the top of each block, or pass --session "dev3-${DEV3_TASK_ID%%-*}" on every command. (If you ever must share one browser machine-wide instead, serialize QA across agents so only one drives at a time.)
• The dev-server is a build snapshot — no watch/HMR. Your code only appears after a (re)start. After changing code, dev3 dev-server restart, re-wait for the port, then agent-browser reload — a bare reload re-serves the old bundle. Don't keep a stale server around; never hand-run vite build.
• Is the running build actually yours? An already-running app/remote is often production or another worktree — it won't have your changes. (Re)start THIS task's dev-server and confirm with dev3 --version (commit hash should match git log -1) + that your change actually renders. Don't assume.
• Tell the user before dev3 dev-server start (visible side effect), and stop it after (step 4) unless they want it kept.
• No DEV3_PORT0? (portCount 0, or an older worktree where it was never allocated) — run your own fixed-port server instead: dev3 remote --no-detach --no-tunnel --static-code $CODE --port 47823 → :47823/?token=$CODE.
• No native dialogs in browser mode. If a confirm/file-picker flow silently no-ops, that's an app bug, not a tooling problem — report it.
• Show images to the user AFTER you stop this dev-server, not while it runs. dev3 show-image (and dev3 attention / dev3 notify) route to the app instance that owns the task — and this QA dev-server is itself a full dev3 instance. While it's up, those UI-attention calls can land in it (the browser only you see) instead of the user's main app, so the user never sees the image. Screenshots persist on disk, so the correct order is capture → dev3 dev-server stop (confirm State: stopped) → dev3 show-image.