fix(core): collapse child agent initial input into a single user message (#589)

strix/core/inputs.py

@@ -136,30 +136,27 @@ def child_initial_input(
     task: str,
     parent_history: list[Any],
 ) -> list[dict[str, Any]]:
-    initial_input: list[dict[str, Any]] = []
+    """Build the initial input for a child agent as a single user message.
+
+    Collapsing the inherited-context block, the identity line, and the task into
+    one ``{"role": "user"}`` message keeps providers that require strictly
+    alternating roles (e.g. Perplexity, llama.cpp) from rejecting consecutive
+    user messages.
+    """
+    parts: list[str] = []
     if parent_history:
         rendered = json.dumps(parent_history, ensure_ascii=False, default=str)
-        initial_input.append(
-            {
-                "role": "user",
-                "content": (
-                    "== Inherited context from parent (background only) ==\n"
-                    f"{rendered}\n"
-                    "== End of inherited context ==\n"
-                    "Use the above as background only; do not continue the "
-                    "parent's work. Your task follows."
-                ),
-            },
+        parts.append(
+            "== Inherited context from parent (background only) ==\n"
+            f"{rendered}\n"
+            "== End of inherited context ==\n"
+            "Use the above as background only; do not continue the "
+            "parent's work. Your task follows.",
         )
-    initial_input.append(
-        {
-            "role": "user",
-            "content": (
-                f"You are agent {name} ({child_id}); your parent is {parent_id}. "
-                "Maintain your own identity. Call agent_finish when your task "
-                "is complete."
-            ),
-        }
+    parts.append(
+        f"You are agent {name} ({child_id}); your parent is {parent_id}. "
+        "Maintain your own identity. Call agent_finish when your task "
+        "is complete.",
     )
-    initial_input.append({"role": "user", "content": task})
-    return initial_input
+    parts.append(task)
+    return [{"role": "user", "content": "\n\n".join(parts)}]

tests/test_inputs.py

@@ -0,0 +1,114 @@
+"""Tests for pure input builders in strix.core.inputs."""
+
+from __future__ import annotations
+
+from itertools import pairwise
+from typing import Any
+
+import pytest
+
+from strix.core.inputs import build_root_task, child_initial_input
+
+
+def _child_kwargs(parent_history: list[Any]) -> dict[str, Any]:
+    return {
+        "name": "scout",
+        "child_id": "agent-2",
+        "parent_id": "agent-1",
+        "task": "Audit the login flow.",
+        "parent_history": parent_history,
+    }
+
+
+def test_child_initial_input_single_message_without_history() -> None:
+    result = child_initial_input(**_child_kwargs([]))
+
+    assert len(result) == 1
+    assert result[0]["role"] == "user"
+    content = result[0]["content"]
+    assert "agent scout (agent-2)" in content
+    assert "Audit the login flow." in content
+    assert "Inherited context" not in content
+
+
+def test_child_initial_input_single_message_with_history() -> None:
+    history = [{"role": "assistant", "content": "previous work"}]
+    result = child_initial_input(**_child_kwargs(history))
+
+    assert len(result) == 1
+    assert result[0]["role"] == "user"
+    content = result[0]["content"]
+    assert "Inherited context from parent" in content
+    assert "previous work" in content
+    assert "agent scout (agent-2)" in content
+    assert "Audit the login flow." in content
+
+
+@pytest.mark.parametrize(
+    "parent_history",
+    [[], [{"role": "assistant", "content": "previous work"}]],
+)
+def test_child_initial_input_no_consecutive_same_role(parent_history: list[Any]) -> None:
+    result = child_initial_input(**_child_kwargs(parent_history))
+
+    roles = [msg["role"] for msg in result]
+    assert all(prev != nxt for prev, nxt in pairwise(roles))
+
+
+def test_build_root_task_empty_config() -> None:
+    assert build_root_task({}) == ""
+
+
+def test_build_root_task_repository_target() -> None:
+    config = {
+        "targets": [
+            {
+                "type": "repository",
+                "details": {
+                    "target_repo": "https://example.com/repo.git",
+                    "cloned_repo_path": "/workspace/repo",
+                    "workspace_subdir": "repo",
+                },
+            },
+        ],
+    }
+    task = build_root_task(config)
+
+    assert "Repositories:" in task
+    assert "/workspace/repo" in task
+    assert "https://example.com/repo.git" in task
+
+
+def test_build_root_task_web_application_with_instructions() -> None:
+    config = {
+        "targets": [
+            {"type": "web_application", "details": {"target_url": "https://app.example.com"}},
+        ],
+        "user_instructions": "Focus on auth.",
+    }
+    task = build_root_task(config)
+
+    assert "URLs:" in task
+    assert "https://app.example.com" in task
+    assert "Special instructions: Focus on auth." in task
+
+
+def test_build_root_task_diff_scope() -> None:
+    config = {
+        "targets": [],
+        "diff_scope": {
+            "active": True,
+            "repos": [
+                {
+                    "workspace_subdir": "repo",
+                    "analyzable_files_count": 3,
+                    "deleted_files_count": 2,
+                },
+            ],
+        },
+    }
+    task = build_root_task(config)
+
+    assert "Scope Constraints:" in task
+    assert "3 changed file(s)" in task
+    assert "2 deleted file(s)" in task