feat(channel): unify deliverable outbound and WeChat attachments

Require deliverable:true for all channel attachments including images; extend save_deliverable_attachment with attachment_id; add WeChat proactive attachment delivery; inject channel file rules via system prompt instead of repeating on every user message.

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

tests/test_save_deliverable_attachment_tool.py

@@ -28,3 +28,28 @@ def test_save_deliverable_attachment_registers_file(tmp_path, monkeypatch) -> No
     assert blob is not None
     assert blob.decode("utf-8").replace("\r\n", "\n") == "hello deliverable\n"
     assert meta is not None
+
+
+def test_save_deliverable_attachment_marks_existing_attachment_id(tmp_path, monkeypatch) -> None:
+    from svc.files.attachment_assets import AttachmentAssetStore
+
+    store = AttachmentAssetStore(root_dir=tmp_path / "att")
+    meta = store.save_bytes(b"png-bytes", filename="gen.png", mime="image/png")
+    monkeypatch.setattr(
+        "runtime.tools.public.save_deliverable_attachment_tool.AttachmentAssetStore",
+        lambda root_dir=None: store if root_dir is None else AttachmentAssetStore(root_dir=root_dir),
+    )
+
+    spec = save_deliverable_attachment_tool()
+    out = spec.handler({"attachment_id": meta.attachment_id})
+    assert out.get("ok") is True
+    assert out.get("deliverable") is True
+    assert out.get("attachment_id") == meta.attachment_id
+    assert out.get("mime") == "image/png"
+
+
+def test_save_deliverable_attachment_requires_path_or_attachment_id() -> None:
+    spec = save_deliverable_attachment_tool()
+    out = spec.handler({})
+    assert out.get("ok") is False
+    assert out.get("error") == "path_or_attachment_id_required"