Rename sandbox dir to .bblocks-sandbox and detect stale venvs

Renames the sandbox directory from .transforms-sandbox to .bblocks-sandbox
to reflect that it now hosts both transform and validator plugin venvs.

Also adds a shebang-target check to venv_needs_recreate(): the existing
version check was insufficient when the sandbox directory was renamed,
because pip scripts have an absolute shebang baked in at venv creation
time. Moving the venv silently breaks pip even when the Python version
matches. The new check reads pip's first line and verifies the target
path exists, catching both renamed-sandbox and removed-interpreter cases.

Author: avillar

ogc/bblocks/sandbox.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import re
 import shutil
 import sys
 from pathlib import Path
@@ -8,12 +9,35 @@
 
 _PYTHON_VERSION = f"{sys.version_info.major}.{sys.version_info.minor}.{sys.version_info.micro}"
 
-SANDBOX_DIR_NAME = '.transforms-sandbox'
+SANDBOX_DIR_NAME = '.bblocks-sandbox'
+_OLD_SANDBOX_DIR_NAME = '.transforms-sandbox'
+
+
+def pip_slug(pip_deps: list[str]) -> str:
+    """Return a stable, human-readable directory name for a set of pip specifiers.
+
+    The slug identifies the venv that would result from installing exactly these
+    deps. Same deps → same slug → shared venv. Different version → different slug.
+    """
+    key = ','.join(sorted(pip_deps))
+    slug = re.sub(r'[^a-zA-Z0-9_-]+', '_', key)
+    slug = re.sub(r'_+', '_', slug).strip('_')
+    return slug or 'default'
 
 
 def venv_needs_recreate(venv_dir: Path) -> bool:
-    """Return True if the venv is absent or was built with a different Python version."""
-    if not (venv_dir / 'bin' / 'pip').exists():
+    """Return True if the venv is absent, broken, or was built with a different Python version."""
+    pip_bin = venv_dir / 'bin' / 'pip'
+    if not pip_bin.exists():
+        return True
+    # Verify pip's shebang target still exists (catches renamed sandbox dirs and removed interpreters).
+    try:
+        first_line = pip_bin.read_text(errors='replace').split('\n', 1)[0]
+        if first_line.startswith('#!'):
+            shebang_target = Path(first_line[2:].strip().split()[0])
+            if not shebang_target.exists():
+                return True
+    except OSError:
         return True
     cfg = venv_dir / 'pyvenv.cfg'
     if not cfg.exists():