1 files changed, 96 insertions, 0 deletions
diff --git a/app/backends/sglomni/pythonenv.py b/app/backends/sglomni/pythonenv.py
new file mode 100644
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+++ b/app/backends/sglomni/pythonenv.py
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+"""The sglang-omni venv: interpreter selection and provisioning.
+
+sglang-omni requires Python >=3.10,<3.13 while the app itself is
+version-agnostic — a host whose only ``python`` is 3.13+ must still be
+able to install and run this backend. ``prepare_env`` resolves a usable
+interpreter for the dedicated venv (``app/envs/sglomni``), in order:
+
+1. the venv already exists with an acceptable interpreter (no-op);
+2. the app env's interpreter or a ``python3.10/3.11/3.12`` on PATH fits
+   (the venv is created from it — no download);
+3. uv (pip-installed into the app env) provisions a managed standalone
+   CPython 3.12 into ``app/envs/pythons`` and creates the venv from it —
+   the zero-prerequisites path for hosts like stock Arch, where only the
+   latest Python exists and no root/package-manager knowledge is needed.
+
+An existing venv built with an incompatible interpreter (an older tool
+version, a since-upgraded system Python) is transparently recreated: a
+venv holds nothing user-owned, and every package in it is reinstalled by
+the setup that follows anyway.
+"""
+
+import shutil
+import sys
+from pathlib import Path
+from typing import Optional, Tuple
+
+from backends import common, envs
+from backends.sglomni.constants import PYTHON_SPEC, PYTHON_VERSIONS
+
+# The dedicated venv (its interpreter may differ from the launching one).
+SGLOMNI_ENV = envs.SGLOMNI_ENV_DIR
+
+
+def env_version() -> Optional[Tuple[int, int]]:
+    """The (major, minor) Python version of the venv's interpreter."""
+    if not envs.env_exists(SGLOMNI_ENV):
+        return None
+    return envs.python_version(envs.env_python(SGLOMNI_ENV))
+
+
+def env_compatible() -> bool:
+    """True when the venv exists with a Python the sglang-omni stack accepts."""
+    version = env_version()
+    return version is not None and tuple(version) in {tuple(v) for v in PYTHON_VERSIONS}
+
+
+def prepare_env(*, emit=None, cancel=None) -> int:
+    """Make SGLOMNI_ENV exist with a Python in PYTHON_VERSIONS. Returns 0/1.
+
+    The three resolution paths are described in the module docstring; every
+    path ends with a pip-equipped venv so the regular ``python -m pip``
+    helpers (requirements installs, model-companion extras) keep working.
+    Prints what it does so the task view shows why a download happens (or,
+    usually, does not).
+    """
+    if env_compatible():
+        return 0
+    if envs.env_exists(SGLOMNI_ENV):
+        version = env_version()
+        found = f"{version[0]}.{version[1]}" if version else "unknown"
+        print(f"[WARNING] {SGLOMNI_ENV} was built with Python {found}, "
+              "which the sglang-omni stack does not support (needs "
+              "3.10-3.12); recreating it with a compatible interpreter.")
+        # Nothing user-owned lives in the tool-managed venv, and every
+        # package is reinstalled by the steps that follow this one.
+        shutil.rmtree(SGLOMNI_ENV, ignore_errors=True)
+        if SGLOMNI_ENV.exists():
+            print("[ERROR] Could not remove the incompatible venv; "
+                  f"delete {SGLOMNI_ENV} manually and re-run setup.")
+            return 1
+
+    interpreter = envs.compatible_interpreter(PYTHON_VERSIONS)
+    if interpreter is not None:
+        if interpreter == envs.env_python(envs.ENV_DIR):
+            print(f"[INFO] using the app environment's interpreter "
+                  f"({sys.version_info.major}.{sys.version_info.minor}) "
+                  "for the sglang-omni venv.")
+        else:
+            print(f"[INFO] using {interpreter} for the sglang-omni venv.")
+        return envs.create_env(SGLOMNI_ENV, interpreter)
+
+    # No compatible interpreter anywhere: provision one with uv.
+    print("[INFO] no Python 3.10-3.12 found on this system — provisioning "
+          f"a managed CPython {PYTHON_SPEC} with uv (no root required).")
+    rc = envs.ensure_uv(emit=emit, cancel=cancel)
+    if rc != 0:
+        print("[WARNING] pip install uv failed (exit "
+              f"{rc}); install uv manually and re-run setup")
+        return rc
+    rc = envs.provision_env_with_uv(SGLOMNI_ENV, PYTHON_SPEC,
+                                    emit=emit, cancel=cancel)
+    if rc != 0:
+        print(f"[WARNING] uv venv failed (exit {rc}); create the venv "
+              f"manually, e.g.: uv venv --seed --python {PYTHON_SPEC} "
+              f"{SGLOMNI_ENV}")
+    return rc