fix(python-worker): pin uv run to Python >=3.11 so the worker starts on stock macOS

[zaydiscold]

Problem

On a default macOS machine, the Python worker never starts. The TUI reports the opaque:

Error: python worker exited before responding

(and any browser task silently does nothing).

Root cause

PythonWorker::start_with_default_runtime launches the worker with:

uv run --quiet --with cdp-use==1.4.5 --with fetch-use==0.4.0 --with pillow==12.2.0 python -m llm_browser_worker.worker

There's no --python constraint, so uv resolves an interpreter by discovery order. On a stock macOS box that's Apple's frozen /usr/bin/python3 (3.9.6). cdp-use==1.4.5 declares requires-python >= 3.11, so resolution fails:

× No solution found when resolving `--with` dependencies:
╰─▶ Because the current Python version (3.9.6) does not satisfy Python>=3.11
    and cdp-use==1.4.5 depends on Python>=3.11 ...

uv exits non-zero before the worker prints its first line, and read_response_line surfaces that as python worker exited before responding.

Fix

Add --python ">=3.11" to the uv run args. uv will reuse any compatible interpreter already on the machine, or fetch a managed one. No behavior change on hosts that already resolve to >= 3.11.

let args = [
    "run",
    "--quiet",
    "--python",
    ">=3.11",
    "--with", "cdp-use==1.4.5",
    ...
];

Verification

• cargo test -p browser-use-python-worker → 11 passed, 0 failed.
• Before: uv run --with cdp-use==1.4.5 ... python ... from $HOME → resolution error (3.9.6).
• After: uv run --python ">=3.11" --with cdp-use==1.4.5 ... python ... → selects 3.11.x (managed fetch if needed), worker responds {"ok":true,...}, and browser diagnostics reports browser_harness: available.

Notes / possible follow-ups

• The fallback path (python3 with no --with) has the same latent version assumption, but it already depends on a fully provisioned interpreter, so it's out of scope here.
• Separately, read_response_line swallowing the child's stderr is what made this hard to diagnose — surfacing uv's stderr on a non-zero exit would turn "exited before responding" into the actual resolver error. Happy to send that as a second PR if useful.

---

Summary by cubic

Pin uv run to Python >=3.11 (--python ">=3.11") when launching the Python worker so it starts on stock macOS and avoids the "python worker exited before responding" error. uv now reuses a compatible interpreter or fetches one, satisfying cdp-use’s requires-python >= 3.11 with no behavior change on hosts already at >=3.11.

^{Written for commit d96c69a. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}