Add SessionStart hook for dev environment setup

Configures automatic development environment setup for Claude Code web
sessions: upgrades python3 to 3.13+ and clones CPython source if missing.

https://claude.ai/code/session_01VPT2fpdf52qFZLMN8EDNgp

.claude/scripts/setup-env.sh

@@ -0,0 +1,50 @@
+#!/bin/bash
+# Claude Code web session startup script
+# Sets up the development environment for RustPython
+
+set -e
+
+cd /home/user/RustPython
+
+echo "=== RustPython dev environment setup ==="
+
+# 1. Ensure python3 points to 3.13+ (needed for scripts/update_lib)
+#    /usr/local/bin takes precedence over /usr/bin in PATH,
+#    so we update the symlink there directly.
+CURRENT_PY=$(python3 --version 2>&1 | grep -oP '\d+\.\d+')
+if [ "$(printf '%s\n' "3.13" "$CURRENT_PY" | sort -V | head -1)" != "3.13" ]; then
+    echo "Upgrading python3 default to 3.13..."
+    # Find best available Python >= 3.13
+    TARGET=""
+    for ver in python3.14 python3.13; do
+        if command -v "$ver" &>/dev/null; then
+            TARGET=$(command -v "$ver")
+            break
+        fi
+    done
+    if [ -n "$TARGET" ]; then
+        # Override /usr/local/bin/python3 if it exists and is outdated
+        if [ -e /usr/local/bin/python3 ]; then
+            sudo ln -sf "$TARGET" /usr/local/bin/python3
+        fi
+        # Also set /usr/bin via update-alternatives
+        sudo update-alternatives --install /usr/bin/python3 python3 "$TARGET" 3 2>/dev/null || true
+        sudo update-alternatives --set python3 "$TARGET" 2>/dev/null || true
+        echo "python3 now: $(python3 --version)"
+    else
+        echo "WARNING: No Python 3.13+ found. scripts/update_lib may not work."
+    fi
+else
+    echo "python3 already >= 3.13: $(python3 --version)"
+fi
+
+# 2. Clone CPython source if not present (needed for scripts/update_lib)
+if [ ! -d "cpython" ]; then
+    echo "Cloning CPython v3.14.3 (shallow)..."
+    git clone --depth 1 --branch v3.14.3 https://github.com/python/cpython.git cpython
+    echo "CPython source ready."
+else
+    echo "CPython source already present."
+fi
+
+echo "=== Setup complete ==="

.claude/settings.json

@@ -0,0 +1,15 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "matcher": "",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "bash .claude/scripts/setup-env.sh"
+          }
+        ]
+      }
+    ]
+  }
+}