handoff fixes

backend/tests/test_external_reply_service.py

@@ -1,6 +1,10 @@
 from bson import ObjectId
 
-from app.services.external_reply_service import build_external_reply_plan
+from app.services.external_reply_service import (
+    build_external_reply_plan,
+    internet_message_id_of,
+)
+from app.services.message_ids import canonical_message_id, folded_message_id
 from app.services.thread_service import threading_fields_from_parent
 
 
@@ -55,3 +59,76 @@ def test_external_reply_never_uses_internal_object_id_as_in_reply_to():
     )
     assert str(parent["_id"]) not in (plan.threading.in_reply_to or "")
     assert all(str(parent["_id"]) not in ref for ref in plan.threading.references)
+
+
+def test_handoff_bridge_reply_uses_external_parent_not_human_reply():
+    """Human handoff must thread B against customer A, never private H2."""
+    customer_a = {
+        "_id": ObjectId(),
+        "internet_message_id": "<CAHabc123@mail.gmail.com>",
+        "message_id": "<CAHabc123@mail.gmail.com>",
+        "message_scope": "EXTERNAL",
+        "direction": "inbound",
+        "references": [],
+        "subject": "fresh test",
+    }
+    human_h2 = {
+        "_id": ObjectId(),
+        "internet_message_id": "<H2@gmail.com>",
+        "message_id": "<H2@gmail.com>",
+        "message_scope": "HANDOFF",
+        "direction": "inbound",
+        "in_reply_to": "<H1@gentic.email>",
+        "references": ["<H1@gentic.email>"],
+        "subject": "Re: fresh test",
+    }
+    plan = build_external_reply_plan(
+        parent_external_message=customer_a,
+        body_text="human said B",
+        recipients=["091rabbytes@gmail.com"],
+    )
+    assert plan.threading.in_reply_to == "<CAHabc123@mail.gmail.com>"
+    assert plan.threading.references == ["<CAHabc123@mail.gmail.com>"]
+    assert human_h2["internet_message_id"] not in (plan.threading.in_reply_to or "")
+    assert all(
+        human_h2["internet_message_id"] not in ref for ref in plan.threading.references
+    )
+    assert "<H1@gentic.email>" not in plan.threading.references
+
+
+def test_raw_header_restores_gmail_message_id_case():
+    parent = {
+        "_id": ObjectId(),
+        "internet_message_id": "<cahabc123@mail.gmail.com>",
+        "message_id": "<cahabc123@mail.gmail.com>",
+        "raw_headers": {"message_id": "<CAHabc123@mail.gmail.com>"},
+        "references": [],
+        "subject": "fresh test",
+    }
+    plan = build_external_reply_plan(
+        parent_external_message=parent,
+        body_text="human said B",
+        recipients=["customer@gmail.com"],
+    )
+    assert plan.threading.in_reply_to == "<CAHabc123@mail.gmail.com>"
+    assert plan.threading.references == ["<CAHabc123@mail.gmail.com>"]
+
+
+def test_gmail_message_id_case_is_preserved_for_threading():
+    raw = "<CAHabc123@mail.gmail.com>"
+    assert canonical_message_id(raw) == raw
+    assert folded_message_id(raw) == "<cahabc123@mail.gmail.com>"
+    parent = {
+        "_id": ObjectId(),
+        "internet_message_id": raw,
+        "message_id": raw,
+        "references": [],
+        "subject": "fresh test",
+    }
+    plan = build_external_reply_plan(
+        parent_external_message=parent,
+        body_text="human said B",
+        recipients=["customer@gmail.com"],
+    )
+    assert plan.threading.in_reply_to == raw
+    assert internet_message_id_of(parent) == raw