# Profile Sculptor Backend > Capture Python-level diagnostics from a running Sculptor backend (`sculptor_backend`): instant thread dumps and viztracer/Perfetto traces with no special privileges, or py-spy CPU sampling / flamegraphs / native stacks against the installed signed app (one-time re-sign + sudo). Use when the backend is wedged, slow, pegging a CPU core, or deadlocked, or when you need a CPU profile or a live stack of `sculptor_backend`. Works both INSIDE Sculptor (where privileged steps are delegated to the user so the agent never kills its own backend) and from an EXTERNAL `claude`. - Skill: `imbue-ai/profile-sculptor-backend` (Agent Skill) - Install (CLI): `npx skillmds@latest add imbue-ai/profile-sculptor-backend` - Raw SKILL.md: https://api.skillmd.com/api/skills/imbue-ai/profile-sculptor-backend/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: imbue-ai (https://skillmd.com/u/imbue-ai) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/imbue-ai/profile-sculptor-backend --- # Profile / debug a running Sculptor backend This skill gets Python-level visibility into a live `sculptor_backend` process. There are two routes; **prefer Route A** and fall back to Route B when you need CPU sampling or when the running build predates the in-process debug endpoints. | | Route A — `sculpt debug` (in-process) | Route B — py-spy (attach) | |---|---|---| | **Gives you** | Instant all-thread Python stacks; viztracer→Perfetto call-tree trace | Sampled CPU profile / flamegraph; live stacks; native (C) frames | | **Privileges** | None (HTTP + session token) | `sudo` + a one-time codesign re-sign of the bundle | | **Works on** | Only builds that ship the trace/debug endpoints (probe first) | Any build, including the shipped notarized one | | **Safe inside Sculptor?** | Yes — never touches the process | Re-sign/restart are the user's; the agent only attaches | | **Best for** | "What is every thread doing right now?", a wedged backend, a bounded call-tree trace, CPU-over-time | Instant all-thread stacks (`dump`), a live `top` glance, native (C) frames, CPU profile / flamegraph (`record`). (`record` suspends the target by default — pass `--nonblocking` to avoid freezing a live session; Route A is still richer for over-time CPU.) | > **Why two routes:** macOS blocks `task_for_pid` on the hardened-runtime, > notarized app, so py-spy can't attach until the target is re-signed with > `get-task-allow` (which can't ship on a notarized build — see SCU-1604). The > in-process route sidesteps that entirely but only exists in builds new enough > to include the endpoints. Background: > [`docs/development/tracing.md`](../../../docs/development/tracing.md) (Route A > reference) and SCU-1604. ## Step 0 — Orient: where am I, and what's the target? **Am I inside Sculptor or an external `claude`?** Check `SCULPT_AGENT_ID`: ```bash if [ -n "$SCULPT_AGENT_ID" ]; then echo "INSIDE Sculptor"; else echo "EXTERNAL claude"; fi ``` - **INSIDE Sculptor** (`SCULPT_AGENT_ID` set): the `sculptor_backend` you'd profile is the one hosting this very agent. Route A is safe. For Route B you may build py-spy and attach, but **never** quit/restart the app or kill the backend — that terminates you. Re-sign and restart are the user's actions. - **EXTERNAL `claude`**: you may run the privileged commands directly — codesign (per the always-ask rule in B3) and `sudo py-spy` when passwordless sudo is available (B5). The **app restart is always the user's job** (B4): an external process can't reliably relaunch the user's Sculptor. **Find the running backend (pid, port, binary path):** ```bash pgrep -fl 'sculptor_backend --port' || ps aux | grep '[s]culptor_backend --port' # port (also in $SCULPT_API_PORT / $SCULPTOR_API_PORT when set): ps -o command= -p "$BACKEND_PID" | grep -oE -- '--port [0-9]+' | awk '{print $2}' ``` Derive the bundle executable from the running pid rather than assuming a path (it differs between `Sculptor.app` and `Sculptor Dev.app`); typically `/Applications/Sculptor.app/Contents/Resources/sculptor_backend/sculptor_backend`. ## Step 1 — Is Route A available on this build? (probe) The in-process endpoints only exist in builds that shipped them. Probe: ```bash PORT="${SCULPT_API_PORT:-${SCULPTOR_API_PORT:-5050}}" curl -s -H "x-session-token: $SESSION_TOKEN" "http://localhost:$PORT/api/v1/trace/status" ``` - JSON like `{"enabled":false,...}` → **Route A is available. Use it.** - HTML (`…`) or 404 → endpoints absent in this build → **use Route B (py-spy)**, or install a newer build if in-process tracing is desired. ## Route A — `sculpt debug` (in-process; no privileges) No re-sign, safe from inside Sculptor. If the running build ships the new `sculpt`, use the CLI; otherwise call the endpoints directly with `curl`. The CLI targets the backend via `SCULPT_API_PORT` (default 5050) and authenticates with the session token automatically. **Instant all-thread Python stacks (greenlet-safe; best for a wedged backend):** ```bash sculpt debug threads # to stdout sculpt debug threads -o threads.txt # to a file # Direct equivalent (any build with the endpoint): curl -s -H "x-session-token: $SESSION_TOKEN" "http://localhost:$PORT/api/v1/debug/threads" ``` **Bounded viztracer trace → Perfetto:** ```bash sculpt debug trace start # arm (optionally --tracer-entries N) # …reproduce the slow/interesting activity… sculpt debug trace status # running? buffered counts? sculpt debug trace stop # flush; prints the output path # Direct equivalents: curl -s -XPOST -H "x-session-token: $SESSION_TOKEN" "http://localhost:$PORT/api/v1/trace/start" curl -s -XPOST -H "x-session-token: $SESSION_TOKEN" "http://localhost:$PORT/api/v1/trace/stop" ``` Open the resulting `trace-.json` (written under the backend's `{LOG_PATH}/traces/` — `~/.sculptor/internal/logs/traces/` in a normal install; the exact path is returned by `stop`) at . This is the runtime side of the tracing system; see [`docs/development/tracing.md`](../../../docs/development/tracing.md) for the full reference (what's captured, sources/pids, clock caveat, sensitive-data handling, endpoint security). Operationally: only one trace runs at a time (`start` → 409 if already armed); the ring buffer holds `DEFAULT_ADHOC_TRACER_ENTRIES` events by default (bounded server-side; raise with `--tracer-entries`) and wraps when full; and a runtime-armed trace is **backend-Python only** — for renderer/Electron-main lanes you need a from-boot `sculptor --trace-to=` run (see tracing.md). ## Route B — py-spy (attach; CPU sampling, flamegraphs, native stacks) ### B1. Get a working py-spy Stock py-spy mis-resolves the bundled `libpython` image base in our PyInstaller onedir layout and fails with `Unsupported version of Python: 0.0.0`. The fix is upstream in **benfred/py-spy#858** ("Adjust the PyInstaller MacOS image base"). py-spy source — pick the first that applies: 1. **Official, once #858 ships in a release** — prefer plain `cargo install py-spy` / a released binary. Check whether #858 has landed: `gh pr view 858 --repo benfred/py-spy --json state,mergedAt`. 2. **Until then, build the fork branch** (needs Rust/`cargo`) and cache it: ```bash # Override PYSPY to point at any working build (e.g. a released py-spy once #858 lands). PYSPY="${PYSPY:-$HOME/.cache/sculptor-pyspy/bin/py-spy}" if ! "$PYSPY" --version >/dev/null 2>&1; then cargo install --git https://github.com/trisiak/py-spy \ --branch pyinstaller-macos-image-base --root "$HOME/.cache/sculptor-pyspy" PYSPY="$HOME/.cache/sculptor-pyspy/bin/py-spy" fi "$PYSPY" --version ``` ### B2. Is a re-sign even required? (inspect first) Check whether the running backend's binary already allows task attachment — don't re-sign blindly (it may already be signed, e.g. from a previous session): ```bash codesign -d --entitlements - "$BACKEND_BIN" 2>&1 | grep -q get-task-allow \ && echo "already attachable — skip B3/B4" || echo "re-sign needed (B3)" ``` If it already has `get-task-allow`, skip to **B5**. **Dev builds (`Sculptor Dev.app`, from `just pkg-dev`) ship the sidecar already signed with `get-task-allow`** (see `forge.config.ts` `postPackage` + `entitlements.dev.plist`), so this check passes and no re-sign is needed — only the notarized production app requires B3. ### B3. Re-sign (only if B2 says so) — always ask the user The shipped backend is hardened-runtime signed without `get-task-allow`, so even `sudo` can't attach. Re-signing **modifies the installed app in place**, **invalidates its notarization seal locally** (fine for dev; persists until the app is reinstalled/updated), and a re-signed file only takes effect after a restart (B4). **Always present the choice to the user — in both internal and external contexts** — and let them pick: - **(a) Agent runs it** — the agent executes the commands below itself. - **(b) User runs it** — hand them the exact commands to run themselves. Either way the commands are: ```bash cat > /tmp/pyspy-entitlements.plist <<'PLIST' com.apple.security.get-task-allow com.apple.security.cs.allow-get-task-allow PLIST codesign -s - -f --entitlements /tmp/pyspy-entitlements.plist "$BACKEND_BIN" codesign -d --entitlements - "$BACKEND_BIN" 2>&1 | grep get-task-allow # verify ``` Re-signing just the `sculptor_backend` executable is sufficient — the bundled `libpython` dylib does not need re-signing. ### B4. Restart — always the user A re-signed on-disk file does not change the already-running process. **Ask the user to restart Sculptor** (quit fully and relaunch) so the new signature takes effect. Never quit/relaunch the app yourself — inside Sculptor it kills you, and externally it isn't reliable. After they confirm the restart, **re-discover the pid and port** (both change) via Step 0. ### B5. Attach and profile py-spy needs root. Try passwordless sudo; if it isn't available, hand the exact command to the user instead of prompting blindly. ```bash if sudo -n true 2>/dev/null; then RUN="sudo -n"; else echo "No passwordless sudo — ask the user to run the command below themselves."; RUN="sudo" fi $RUN "$PYSPY" dump --pid "$BACKEND_PID" # one-shot all-thread stacks (brief pause) $RUN "$PYSPY" top --pid "$BACKEND_PID" # live top-functions view # add --native for C frames # CPU profile / flamegraph over time. --nonblocking is essential against a live # backend (see note below): it samples without suspending the process. $RUN "$PYSPY" record --pid "$BACKEND_PID" --nonblocking --rate 50 --duration 20 \ --output ~/sculptor-backend-flame.svg # open in any browser # Scrubbable timeline instead of a flat flamegraph (open at https://speedscope.app): $RUN "$PYSPY" record --pid "$BACKEND_PID" --nonblocking --rate 50 --duration 20 \ --format speedscope --output ~/sculptor-backend-profile.speedscope.json ``` **`py-spy record` against the backend: pass `--nonblocking`.** By default py-spy samples by *suspending* the target, and `record`'s continuous suspend-sample over a duration blocks the backend heavily on macOS — enough to freeze a live session (and inside Sculptor that's the very session you're running in). `--nonblocking` reads stacks without pausing the process, so it doesn't freeze anything; the tradeoff is occasional partial/inconsistent stacks and higher sampling error, which is usually fine for a hotspot flamegraph. Keep `--rate` modest and `--duration` bounded regardless. For the **richest over-time CPU picture, Route A viztracer is still better** — it runs in-process with a full call tree — but when Route A is absent (the build that pushed you to Route B), `--nonblocking record` is the right fallback. `dump`/`top` pause only briefly and don't need the flag. ## Cleanup - Stop any armed Route-A trace (`sculpt debug trace stop`) you started. - The re-signed bundle stays re-signed; tell the user they can reinstall/update to restore the pristine notarized app. ## Pitfalls - **Don't kill your own backend / app.** Inside Sculptor, the restart in B4 is always the user's action. - **pid/port change on restart** — re-discover them (Step 0) after any relaunch. - **Inspect before re-signing** (B2) — the binary may already be attachable. - **Stock py-spy fails** with `0.0.0` on our bundle — use the patched fork (B1). - **`py-spy record` blocks the backend by default** (suspend-based continuous sampling) — pass **`--nonblocking`** to sample without pausing the process, or use Route A viztracer for the richest sustained CPU profile (B5). - **One Route-A trace at a time** (`start` → 409 if already running).