feat: inject agents XML block (0.2.2)

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "pytest-codingagents"
-version = "0.2.1"
+version = "0.2.2"
 description = "Pytest plugin for testing real coding agents via their SDK"
 readme = "README.md"
 license = { text = "MIT" }

src/pytest_codingagents/copilot/personas.py

@@ -179,6 +179,8 @@ def apply(
         if agent.custom_agents:
             tool = _make_runsubagent_tool(agent, agent.custom_agents, mapper)
             _inject_tool(session_config, tool)
+            agents_block = _build_agents_block(agent.custom_agents, tool_name="runSubagent")
+            _prepend_system_message(session_config, agents_block)
 
 
 # ---------------------------------------------------------------------------
@@ -215,6 +217,8 @@ def apply(
         if agent.custom_agents:
             tool = _make_task_tool(agent, agent.custom_agents, mapper)
             _inject_tool(session_config, tool)
+            agents_block = _build_agents_block(agent.custom_agents, tool_name="task")
+            _prepend_system_message(session_config, agents_block)
 
 
 # ---------------------------------------------------------------------------
@@ -249,6 +253,44 @@ def _inject_tool(session_config: dict[str, Any], tool: "Tool") -> None:
     session_config["tools"] = existing + [tool]
 
 
+def _build_agents_block(custom_agents: list[dict[str, Any]], tool_name: str = "runSubagent") -> str:
+    """Build the <agents> XML block that VS Code injects into the system prompt.
+
+    Mirrors ``computeAutomaticInstructions.ts`` in ``microsoft/vscode``:
+    lists available subagents by name and description so the model knows
+    which agents to dispatch and how to call them.
+
+    Args:
+        custom_agents: List of custom agent config dicts (each with at least
+            a ``name`` key, optionally ``description`` and ``argument_hint``).
+        tool_name: Name of the dispatch tool (``runSubagent`` for VS Code,
+            ``task`` for Claude Code).
+
+    Returns:
+        The ``<agents>…</agents>`` XML string to prepend to the system message.
+    """
+    lines: list[str] = [
+        "<agents>",
+        "Here is a list of agents that can be used when running a subagent.",
+        (
+            "Each agent has optionally a description with the agent's purpose "
+            "and expertise. When asked to run a subagent, choose the most "
+            "appropriate agent from this list."
+        ),
+        f"Use the {tool_name} tool with the agent name to run the subagent.",
+    ]
+    for a in custom_agents:
+        lines.append("<agent>")
+        lines.append(f"<name>{a['name']}</name>")
+        if desc := a.get("description"):
+            lines.append(f"<description>{desc}</description>")
+        if hint := a.get("argument_hint") or a.get("argumentHint"):
+            lines.append(f"<argumentHint>{hint}</argumentHint>")
+        lines.append("</agent>")
+    lines.append("</agents>")
+    return "\n".join(lines)
+
+
 def _make_runsubagent_tool(
     parent_agent: "CopilotAgent",
     custom_agents: list[dict[str, Any]],