feat: deployment-level no_shell policy (agents.yaml no_shell: true)

fast-agent auto-activates its shell execute tool on any agent with
skills configured, and Context.no_shell — the only opt-out — has no
constructor or config knob. Add install_no_shell(), a wrapper on
fast_agent.context.initialize_context that stamps no_shell=True on
every context, installed from server.main() when the deployment's
agents.yaml sets a truthy top-level no_shell: key. Skill loading via
read_skill is unaffected. Default behaviour unchanged for deployments
without the key.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pallas/_fastagent_patch.py

@@ -474,3 +474,36 @@ def install() -> None:
     _patch_create_session_factory()
     _patch_aggregator_call_tool()
 
+
+def install_no_shell() -> None:
+    """Disable fast-agent's shell runtime for every agent in this process.
+
+    fast-agent auto-activates its ``execute`` shell tool on any agent that
+    has skills configured (``MCPAgent._ensure_shell_runtime_for_skills``);
+    the only opt-out is ``Context.no_shell``, which fast-agent's own CLI
+    sets by direct assignment but which has no ``FastAgent``-constructor or
+    config-file knob.  The context is created inside ``run()`` before agents
+    are constructed, so we wrap ``initialize_context`` to stamp the flag on
+    every context it returns.  Skill loading itself is unaffected — the
+    ``read_skill`` tool registers independently of the shell.
+
+    NOT installed by ``install()``: this is deployment policy, not a runtime
+    fix.  ``server.main()`` calls it when the deployment's ``agents.yaml``
+    sets a truthy top-level ``no_shell:`` key.
+    """
+    from fast_agent import context as _fa_context
+
+    if getattr(_fa_context.initialize_context, "_pallas_no_shell_patched", False):
+        return
+
+    _original_initialize_context = _fa_context.initialize_context
+
+    async def _initialize_context_no_shell(*args: Any, **kwargs: Any):
+        ctx = await _original_initialize_context(*args, **kwargs)
+        ctx.no_shell = True
+        return ctx
+
+    _initialize_context_no_shell._pallas_no_shell_patched = True  # type: ignore[attr-defined]
+    _fa_context.initialize_context = _initialize_context_no_shell
+    logger.info("no_shell patch installed — agents will not get the shell tool")
+

pallas/server.py

@@ -18,6 +18,7 @@ from pathlib import Path
 
 import yaml
 
+from pallas import _fastagent_patch
 from pallas.log import set_agent_component, set_project, setup_logging
 from pallas.multimodal_server import MultimodalAgentMCPServer
 
@@ -390,6 +391,13 @@ def main() -> None:
 
     setup_logging()
 
+    # Team-level policy: a truthy top-level ``no_shell:`` in agents.yaml
+    # keeps fast-agent's shell tool off every agent in this deployment
+    # (it otherwise auto-activates on agents with skills configured).
+    # After setup_logging() so the install log record isn't lost.
+    if config.get("no_shell"):
+        _fastagent_patch.install_no_shell()
+
     if args.agent:
         port = agents[args.agent]["port"]
         logger.info("Starting %s agent on port %d", args.agent, port)

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "pallas-mcp"
-version = "0.5.1"
+version = "0.5.2"
 description = "FastAgent MCP Bridge — generic runtime for serving FastAgent agents over StreamableHTTP"
 requires-python = ">=3.13.5"
 dependencies = [