diff --git a/docker/Dockerfile b/docker/Dockerfile
index 1aeb43a4..efa4ecb6 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -1,9 +1,9 @@
 # Dockerfile for Ubuntu 24.04 with C++ development tools.
 FROM ubuntu:24.04
+SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 
 # Install gcc, clang and some supporting tools for downloading/installing later tools.
 RUN apt-get update && apt-get install -y --no-install-recommends \
-    cmake \
     curl \
     g++ \
     gdb \
@@ -21,6 +21,12 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     wget \
 && rm -rf /var/lib/apt/lists/*
 
+# Install newer CMake from kitware.
+RUN wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | gpg --dearmor - | tee /etc/apt/trusted.gpg.d/kitware.gpg >/dev/null \
+&& apt-add-repository -y 'deb https://apt.kitware.com/ubuntu/ noble main' \
+&& apt-get update && apt-get install -y --no-install-recommends cmake \
+&& rm -rf /var/lib/apt/lists/*
+
 # Install bazelisk.
 RUN ARCH=$(dpkg --print-architecture) && \
     wget https://github.com/bazelbuild/bazelisk/releases/download/v1.25.0/bazelisk-linux-${ARCH} -O /usr/local/bin/bazelisk \
@@ -32,26 +38,26 @@ RUN useradd -m -s /bin/bash vscode \
     && mkdir -p /workspace \
     && chown vscode:vscode /workspace
 
-# Install Node.js (required for Gemini CLI)
+# Install Node.js (required for Claude Code)
 RUN curl -fsSL https://deb.nodesource.com/setup_20.x | bash - \
     && apt-get install -y --no-install-recommends nodejs \
     && rm -rf /var/lib/apt/lists/*
 
-# Install Gemini CLI globally
-RUN npm install -g @google/gemini-cli
-
 # Switch to non-root user
 USER vscode
 WORKDIR /workspace
 
+# Configure npm for user-local global installs.
+ENV NPM_CONFIG_PREFIX=/home/vscode/.npm-global
+ENV PATH="/home/vscode/.npm-global/bin:/home/vscode/.local/bin:/usr/local/bin:${PATH}"
+RUN mkdir -p /home/vscode/.npm-global
+
+# Install Claude Code CLI.
+RUN npm install -g @anthropic-ai/claude-code
+
+# Install Antigravity CLI (installs binary as `agy` into ~/.local/bin).
+RUN curl -fsSL https://antigravity.google/cli/install.sh | bash
+
 # Set up uv and Python environment
 RUN curl -LsSf https://astral.sh/uv/install.sh | sh
-
-# Set up environment variables
-ENV PATH="/home/vscode/.local/bin:/usr/local/bin:${PATH}"
 ENV UV_PROJECT_ENVIRONMENT="/home/vscode/.venv"
-
-# Pre-configure Gemini CLI
-RUN mkdir -p /home/vscode/.gemini \
-    && echo '{"/workspace": "TRUST_FOLDER"}' > /home/vscode/.gemini/trustedFolders.json \
-    && echo '{"security": {"auth": {"selectedType": "gemini-api-key"}}}' > /home/vscode/.gemini/settings.json
diff --git a/scripts/agentic-sandbox.py b/scripts/agentic-sandbox.py
new file mode 100644
index 00000000..16c105b5
--- /dev/null
+++ b/scripts/agentic-sandbox.py
@@ -0,0 +1,167 @@
+#!/usr/bin/env python3
+"""
+Script to run an AI agent in a Docker sandbox.
+
+Supported agents: Claude Code, Antigravity CLI.
+"""
+
+import argparse
+import os
+import subprocess
+import sys
+
+
+def _seed_config_file(path: str, content: bytes) -> None:
+    """
+    Create path with content and mode 0o600.
+
+    Skips silently if it already exists.
+    """
+    try:
+        fd = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+    except FileExistsError:
+        return
+    try:
+        os.write(fd, content)
+    finally:
+        os.close(fd)
+
+
+def main() -> None:
+    """Provide the main entry point for the agentic sandbox script."""
+    parser = argparse.ArgumentParser(
+        description="Run an AI agent (claude or antigravity)"
+        " in a Docker sandbox."
+    )
+    parser.add_argument(
+        "agent",
+        choices=["claude", "antigravity"],
+        help="AI agent to run inside the sandbox.",
+    )
+    parser.add_argument(
+        "--update",
+        action="store_true",
+        help="Update the agent CLI inside the container before running.",
+    )
+    parser.add_argument(
+        "--rebuild-docker", action="store_true", help="Rebuild the Docker image."
+    )
+    parser.add_argument(
+        "-v", "--verbose", action="store_true", help="Enable verbose logging."
+    )
+
+    args = parser.parse_args()
+
+    def log(msg: str) -> None:
+        """Log a message if verbose mode is enabled."""
+        if args.verbose:
+            print(msg)
+
+    project_root = subprocess.check_output(
+        ["git", "rev-parse", "--show-toplevel"], text=True
+    ).strip()
+
+    image_name = "cc-protocol-sandbox"
+
+    image_exists = (
+        subprocess.run(
+            ["docker", "image", "inspect", image_name],
+            capture_output=True,
+        ).returncode
+        == 0
+    )
+
+    if args.rebuild_docker or not image_exists:
+        log(f"--- Building Docker Sandbox: {image_name} ---")
+        subprocess.check_call(
+            [
+                "docker",
+                "build",
+                "-t",
+                image_name,
+                "-f",
+                os.path.join(project_root, "docker/Dockerfile"),
+                project_root,
+            ]
+        )
+
+    log(f"--- Starting Sandboxed {args.agent.capitalize()} Session ---")
+    log(f"Note: Your current directory {project_root} is mounted to /workspace")
+
+    if args.agent == "antigravity":
+        npm_package = None
+        agent_cmd = "agy"
+    else:
+        npm_package = "@anthropic-ai/claude-code"
+        agent_cmd = "claude --dangerously-skip-permissions"
+
+    if args.update:
+        if args.agent == "antigravity":
+            container_cmd = (
+                "curl -fsSL https://antigravity.google/cli/install.sh | bash && "
+                f"{agent_cmd}"
+            )
+        else:
+            container_cmd = (
+                f"export NPM_CONFIG_PREFIX=~/.npm-global && "
+                f"export PATH=~/.npm-global/bin:$PATH && "
+                f"npm install -g {npm_package}@latest && {agent_cmd}"
+            )
+    else:
+        container_cmd = agent_cmd
+
+    run_args = [
+        "docker",
+        "run",
+        "-it",
+        "--rm",
+        "-v",
+        f"{project_root}:/workspace",
+    ]
+
+    if args.agent == "antigravity":
+        antigravity_config_dir = os.path.expanduser("~/.gemini")
+        os.makedirs(antigravity_config_dir, mode=0o700, exist_ok=True)
+        # Seed default config files if missing so they are accessible inside the
+        # container.
+        # Use os.open with restrictive permissions to avoid exposing credentials to
+        # other local users on multi-user systems.
+        _seed_config_file(
+            os.path.join(antigravity_config_dir, "trustedFolders.json"),
+            b'{"/workspace": "TRUST_FOLDER"}',
+        )
+        _seed_config_file(
+            os.path.join(antigravity_config_dir, "settings.json"),
+            b'{"selectedAuthType": "oauth-personal"}',
+        )
+        run_args.extend(["-v", f"{antigravity_config_dir}:/home/vscode/.gemini"])
+    else:
+        host_claude_dir = os.path.expanduser("~/.claude")
+        host_claude_json = os.path.expanduser("~/.claude.json")
+        os.makedirs(host_claude_dir, mode=0o700, exist_ok=True)
+        # Ensure the file exists on the host so Docker doesn't create it as a directory.
+        # Use os.open with restrictive permissions to avoid exposing credentials to
+        # other local users on multi-user systems.
+        if os.path.exists(host_claude_json):
+            if not os.path.isfile(host_claude_json):
+                sys.exit(
+                    f"Expected {host_claude_json} to be a regular file, but found a "
+                    "different filesystem object. Remove or rename it and rerun."
+                )
+        else:
+            _seed_config_file(host_claude_json, b"")
+        run_args.extend(["-v", f"{host_claude_dir}:/home/vscode/.claude"])
+        run_args.extend(["-v", f"{host_claude_json}:/home/vscode/.claude.json"])
+
+    if "TERM" in os.environ:
+        run_args.extend(["-e", f"TERM={os.environ['TERM']}"])
+    if "COLORTERM" in os.environ:
+        run_args.extend(["-e", f"COLORTERM={os.environ['COLORTERM']}"])
+
+    run_args.extend([image_name, "bash", "-c", container_cmd])
+
+    subprocess.run(run_args, check=True)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/agentic-sandbox.sh b/scripts/agentic-sandbox.sh
new file mode 100755
index 00000000..451ec5d4
--- /dev/null
+++ b/scripts/agentic-sandbox.sh
@@ -0,0 +1,10 @@
+#!/bin/bash
+
+set -eu -o pipefail
+
+# Get the workspace root
+WORKSPACE_ROOT=$(git rev-parse --show-toplevel)
+
+# Change directory to the workspace root and run the python script
+cd "$WORKSPACE_ROOT"
+uv run scripts/agentic-sandbox.py "$@"
diff --git a/scripts/gemini-sandbox.sh b/scripts/gemini-sandbox.sh
deleted file mode 100755
index 955c04c5..00000000
--- a/scripts/gemini-sandbox.sh
+++ /dev/null
@@ -1,31 +0,0 @@
-#!/bin/bash
-
-# Exit on error
-set -euo pipefail
-
-# Check if GEMINI_API_KEY is set
-if [ -z "$GEMINI_API_KEY" ]; then
-    echo "Error: GEMINI_API_KEY environment variable is not set."
-    echo "Please set it before running this script:"
-    echo "  export GEMINI_API_KEY='your_api_key_here'"
-    exit 1
-fi
-
-IMAGE_NAME="value-types-sandbox"
-DOCKERFILE="docker/Dockerfile"
-
-# Build the image
-echo "--- Building Docker Sandbox: $IMAGE_NAME ---"
-docker build -t "$IMAGE_NAME" -f "$DOCKERFILE" .
-
-# Run the container
-echo "--- Starting Sandboxed Gemini Session ---"
-echo "Note: Your current directory $(pwd) is mounted to /workspace"
-
-docker run -it --rm \
-    -v "$(pwd):/workspace" \
-    -e GEMINI_API_KEY="$GEMINI_API_KEY" \
-    -e TERM=${TERM:-} \
-    -e COLORTERM=${COLORTERM:-} \
-    "$IMAGE_NAME" \
-    gemini