browser-trace

# Browser Trace

Attach a **second, read-only CDP client** to a browser session that is already being driven by your main automation. The trace records the full DevTools firehose to NDJSON, polls for screenshots and DOM dumps in parallel, and slices everything into a directory tree that bash tools can search.

This skill does **not** drive pages — it only listens. Pair it with the `browser` skill, `browse`, Stagehand, Playwright, or anything else that speaks CDP.

## When to use

- The user wants to debug a browser-automation run (failing form, missing element, hung navigation, JS exception).
- The user has a running automation and wants to attach a trace mid-flight without restarting it.
- The user wants to split a CDP firehose into network / console / DOM / page buckets.
- The user wants screenshots + DOM snapshots over time, joined to CDP events by timestamp.

If the user just wants to **drive** the browser, use the `browser` skill instead.

## Setup check

```bash
node --version                                  # require Node 18+
which browse || npm install -g browse
which jq     || true                                # optional — used only for ad-hoc querying
```

Verify `browse cdp` exists:

```bash
browse --help | grep -q "^\s*cdp " || echo "browse cdp not available — update browse"
```

## How it works

Every Chrome DevTools target accepts **multiple concurrent CDP clients**. Your main automation is one client; this skill adds a second one that only enables observation domains (Network, Console, Runtime, Log, Page) and never sends action commands.

The tracer has three pieces:

1. **Firehose**: `browse cdp <target>` streams every CDP event as one JSON object per line to `cdp/raw.ndjson`.
2. **Sampler**: a polling loop calls `browse screenshot --cdp <target> --path <file>` and `browse get html body --cdp <target>` on an interval (default 2s). The helper passes `--cdp` when it samples so it can attach to the traced target from its own process; once a browse daemon session is attached to a CDP target, follow-up commands in that session do not need to repeat `--cdp`.
3. **Bisector**: after the run, `bisect-cdp.mjs` walks `raw.ndjson` once, slices it into per-bucket JSONL files keyed by CDP method, and additionally bisects per page using top-level `Page.frameNavigated` events as boundaries.

## Quickstart

### Local Chrome

```bash
# 1. Launch Chrome with a debugger port (any user-data-dir keeps it isolated).
"/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" \
  --remote-debugging-port=9222 \
  --user-data-dir=/tmp/chrome-o11y \
  about:blank &

# 2. Start the tracer.
node scripts/start-capture.mjs 9222 my-run

# 3. Run your main automation against port 9222.
browse open https://example.com --cdp 9222
# ...whatever the run does...

# 4. Stop and bisect.
node scripts/stop-capture.mjs my-run
node scripts/bisect-cdp.mjs my-run
```

### Browserbase remote

Two helpers wrap the platform-side bookkeeping: `bb-capture.mjs` creates or attaches to a session and starts the tracer; `bb-finalize.mjs` pulls platform artifacts (final session metadata, server logs, downloads) into the run dir at the end.

> Browserbase ends a session as soon as its last CDP client disconnects. **Create with `--keep-alive`, then attach automation to the session's `connectUrl` before or together with the tracer.** `bb-capture.mjs --new` handles the keep-alive session and tracer setup; your automation still needs to attach.

```bash
export BROWSERBASE_API_KEY=...

# 1. Create a keep-alive session AND start the tracer in one step.
#    Prints the session id, connectUrl prefix, and a live debugger URL you
#    can open in a browser to watch the run interactively.
node scripts/bb-capture.mjs --new my-run

# 2. Drive automation. bb-capture stamped the session id into the manifest.
SID=$(jq -r .browserbase.session_id .o11y/my-run/manifest.json)
CONNECT_URL="$(browse cloud sessions get "$SID" | jq -r .connectUrl)"
BROWSE_NAME=my-run-browser
browse open https://example.com --cdp "$CONNECT_URL" --session "$BROWSE_NAME"
browse open https://news.ycombinator.com --session "$BROWSE_NAME"

# 3. Stop the tracer, bisect, then pull platform artifacts and release.
node scripts/stop-capture.mjs my-run
node scripts/bisect-cdp.mjs my-run
node scripts/bb-finalize.mjs my-run --release
```

Attaching to a session that's *already running* (e.g. one your production worker created) — `bb-capture.mjs` accepts a session id instead of `--new`:

```bash
# Pick a running session (filter client-side; browse cloud sessions list has no --status flag)
browse cloud sessions list | jq -r '.[] | select(.status == "RUNNING") | .id'

node scripts/bb-capture.mjs <session-id> mid-flight-debug
# ...tracer runs alongside the existing automation client; no disruption...
node scripts/stop-capture.mjs mid-flight-debug
node scripts/bisect-cdp.mjs mid-flight-debug
node scripts/bb-finalize.mjs mid-flight-debug   # without --release: leave the session running
```

#### What you get from the Browserbase platform

`bb-capture.mjs` adds a `browserbase` block to `manifest.json` (session id, project, region, started_at, expires_at, debugger URL). `bb-finalize.mjs` writes:

- `<run>/browserbase/session.json` — final `browse cloud sessions get` snapshot (proxyBytes, status, ended_at, viewport, …)
- `<run>/browserbase/logs.json` — `browse cloud sessions logs` output. **Often empty.** The CDP firehose in `cdp/raw.ndjson` is the source of truth; this is a side channel.
- `<run>/browserbase/downloads.zip` — files the session downloaded, if any (the script discards the empty 22-byte zip you get when there are none)

Session replay artifact fetching is **deprecated** and isn't fetched. Use the screenshots + DOM dumps in `screenshots/` and `dom/` for visual ground truth.

The live `debugger_url` in the manifest opens an interactive Chrome DevTools view served by Browserbase — handy for *watching* a long-running automation while the tracer captures the firehose to disk.