fix(gateway): reject PM-created documentation subtasks (#163)

Smoke-12: be-pm delegated TWO subtasks under one cell parent — a
code subtask (be-dev-1, spawned) and a documentation subtask
(be-dev-2). The orchestrator dev-dispatch refuses to spawn a developer
for task_type=documentation, so the doc subtask became a permanent
orphan that loops dev-dispatch forever and would deadlock submit_up
(all subtasks must be terminal). The spine-cap is per-type so
code + documentation both passed sibling-dedup — the PM never saw the
anti-pattern warning.

_delegate_static_guards now rejects task_type='documentation' with a
remediate explaining the lifecycle auto-creates the documentation
phase (awaiting_documentation → documenter spawned) after the code
subtask passes QA, and that the PM should delegate ONLY the code
subtask.

tests/unit/gateway/test_delegate_rejects_documentation_subtask.py

@@ -0,0 +1,135 @@
+"""Task #163: delegate() rejects PM-created documentation subtasks.
+
+Smoke-12: be-pm delegated TWO subtasks under one cell parent — a
+`code` subtask (be-dev-1, spawned) and a `documentation` subtask
+(be-dev-2). The orchestrator's dev-dispatch refuses to spawn a
+developer for a documentation task_type, so the doc subtask became a
+permanent orphan that would deadlock submit_up (all subtasks must be
+terminal). The spine-cap is per-type so code+documentation both passed
+the sibling-dedup. Fix: _delegate_static_guards rejects
+task_type='documentation' with a remediate explaining the lifecycle
+auto-handles docs after the code subtask passes QA.
+"""
+
+from __future__ import annotations
+
+from datetime import UTC, datetime
+from typing import Any
+from unittest.mock import AsyncMock, MagicMock
+from uuid import uuid4
+
+import pytest
+from roboco.services.gateway.choreographer import Choreographer, ChoreographerDeps
+from roboco.services.gateway.choreographer._impl import DelegateInputs
+
+
+def _make_deps(**overrides: Any) -> ChoreographerDeps:
+    base: dict[str, Any] = {
+        "task": AsyncMock(),
+        "work_session": AsyncMock(),
+        "git": AsyncMock(),
+        "a2a": AsyncMock(),
+        "journal": AsyncMock(),
+        "audit": AsyncMock(),
+        "evidence_repo": AsyncMock(),
+        "messaging": AsyncMock(),
+    }
+    base.update(overrides)
+    repo = base["evidence_repo"]
+    for m in (
+        "list_unread_a2a",
+        "list_unread_mentions",
+        "list_pending_notifications",
+        "task_metadata_gaps",
+        "recent_team_activity",
+        "blockers_in_lane",
+        "journal_highlights_for_task",
+    ):
+        getattr(repo, m).return_value = []
+    _ldef = base["journal"].latest_decision_at.return_value
+    if type(_ldef).__name__ in ("MagicMock", "AsyncMock"):
+        base["journal"].latest_decision_at.return_value = datetime.now(UTC)
+    return ChoreographerDeps(**base)
+
+
+def _parent(parent_id: object) -> MagicMock:
+    return MagicMock(
+        id=parent_id,
+        project_id=uuid4(),
+        team="backend",
+        status="in_progress",
+        task_type="planning",
+        sequence=0,
+        assigned_to=uuid4(),
+    )
+
+
+def _inputs(task_type: str) -> DelegateInputs:
+    return DelegateInputs(
+        title="Doc the change",
+        description="Write documentation for the README change",
+        acceptance_criteria=["doc created", "doc linked"],
+        assigned_to="be-dev-2",
+        team="backend",
+        task_type=task_type,
+        nature="technical",
+        estimated_complexity="medium",
+    )
+
+
+@pytest.mark.asyncio
+async def test_delegate_rejects_documentation_task_type() -> None:
+    """A documentation-typed subtask is rejected with a lifecycle hint."""
+    pm_id = uuid4()
+    parent_id = uuid4()
+    deps = _make_deps()
+    c = Choreographer(deps)
+
+    env = await c._delegate_static_guards(
+        pm_id, parent_id, _parent(parent_id), _inputs("documentation")
+    )
+    assert env is not None, "documentation subtask must be rejected"
+    body = env.as_dict()
+    assert body["error"] == "invalid_state", body
+    remediate = (body["remediate"] or "").lower()
+    assert "task_type='code'" in remediate or "task_type=code" in remediate
+    assert "awaiting_documentation" in remediate or "automatically" in remediate
+    # Must NOT tell the PM to just retry documentation.
+    assert "documenter" in remediate
+
+
+@pytest.mark.asyncio
+async def test_delegate_allows_code_task_type() -> None:
+    """The code subtask (the only thing the PM should delegate) passes
+    the static guard."""
+    pm_id = uuid4()
+    parent_id = uuid4()
+    deps = _make_deps()
+    c = Choreographer(deps)
+
+    env = await c._delegate_static_guards(
+        pm_id, parent_id, _parent(parent_id), _inputs("code")
+    )
+    assert env is None, f"code subtask must pass static guards, got {env}"
+
+
+@pytest.mark.asyncio
+async def test_delegate_still_allows_planning_for_cell_pm() -> None:
+    """Main PM delegating planning to a cell PM is unaffected."""
+    pm_id = uuid4()
+    parent_id = uuid4()
+    deps = _make_deps()
+    c = Choreographer(deps)
+
+    inputs = DelegateInputs(
+        title="Backend slice",
+        description="Own the backend slice end to end",
+        acceptance_criteria=["slice done"],
+        assigned_to="be-pm",
+        team="backend",
+        task_type="planning",
+        nature="technical",
+        estimated_complexity="medium",
+    )
+    env = await c._delegate_static_guards(pm_id, parent_id, _parent(parent_id), inputs)
+    assert env is None, f"planning→cell-PM must pass, got {env}"