feat(channel): deliver generated files on WhatsApp and honor user tool policy

Add save_deliverable_attachment for explicit document outbound, pass channel user_id into tool risk gating so write_file/run_command respect per-user allow_high settings, and document the workflow in channel-file-delivery skill.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_tool_runtime_attachments.py

@@ -3,6 +3,21 @@ from __future__ import annotations
 from runtime.chat.tool_runtime import _attachments_from_tool_result
 
 
+def test_attachments_from_tool_result_preserves_deliverable_flag() -> None:
+    result = {
+        "ok": True,
+        "attachment_id": "att-doc-1",
+        "mime": "text/plain",
+        "name": "out.txt",
+        "bytes": 12,
+        "deliverable": True,
+    }
+    out = _attachments_from_tool_result(result)
+    assert len(out) == 1
+    assert out[0]["type"] == "text_ref"
+    assert out[0].get("deliverable") is True
+
+
 def test_attachments_from_tool_result_preserves_non_image_ref_types() -> None:
     result = {
         "attachments": [