human handoffs

backend/tests/test_thread_resolver.py

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+from datetime import datetime, timezone
+from bson import ObjectId
+
+from app.services.message_ids import build_references_header, normalize_message_id, parse_message_id_list
+from app.services.subject_normalize import normalize_subject
+from app.services.thread_resolver import KnownMessage, resolve_thread_from_known
+
+
+def _known(
+    internet_id: str,
+    thread_id: ObjectId,
+    account_id: str = "acct-1",
+    participants: frozenset[str] | None = None,
+) -> KnownMessage:
+    now = datetime.now(timezone.utc)
+    return KnownMessage(
+        id=ObjectId(),
+        thread_id=thread_id,
+        internet_message_id=normalize_message_id(internet_id) or "",
+        account_id=account_id,
+        sent_at=now,
+        received_at=now,
+        created_at=now,
+        participants=participants or frozenset({"sender@example.com"}),
+        normalized_subject=normalize_subject("Project update"),
+    )
+
+
+def test_new_message_creates_new_thread():
+    resolution = resolve_thread_from_known(
+        account_id="acct-1",
+        in_reply_to=None,
+        references=[],
+        subject="Project update",
+        participants={"sender@example.com"},
+        known_by_internet_id={},
+    )
+    assert resolution.thread_id is None
+    assert resolution.thread_resolution_method == "new_thread"
+    assert resolution.thread_relation == "new_thread"
+
+
+def test_direct_reply_matches_in_reply_to():
+    thread_id = ObjectId()
+    parent = _known("<a@gentic.email>", thread_id)
+    known = {parent.internet_message_id: parent}
+    resolution = resolve_thread_from_known(
+        account_id="acct-1",
+        in_reply_to="<a@gentic.email>",
+        references=["<a@gentic.email>"],
+        subject="Re: Project update",
+        participants={"rahul@example.com"},
+        known_by_internet_id=known,
+    )
+    assert resolution.thread_id == thread_id
+    assert resolution.thread_resolution_method == "in_reply_to"
+    assert resolution.parent_message_id == parent.id
+
+
+def test_references_fallback_when_parent_missing():
+    thread_id = ObjectId()
+    parent = _known("<a@gentic.email>", thread_id)
+    known = {parent.internet_message_id: parent}
+    resolution = resolve_thread_from_known(
+        account_id="acct-1",
+        in_reply_to="<b@example.com>",
+        references=["<a@gentic.email>", "<b@example.com>"],
+        subject="Re: Project update",
+        participants={"rahul@example.com"},
+        known_by_internet_id=known,
+    )
+    assert resolution.thread_id == thread_id
+    assert resolution.thread_resolution_method == "references"
+
+
+def test_fake_re_subject_does_not_thread():
+    thread_id = ObjectId()
+    parent = _known("<a@gentic.email>", thread_id)
+    known = {parent.internet_message_id: parent}
+    resolution = resolve_thread_from_known(
+        account_id="acct-1",
+        in_reply_to=None,
+        references=[],
+        subject="Re: Project update",
+        participants={"rahul@example.com"},
+        known_by_internet_id=known,
+    )
+    assert resolution.thread_id is None
+    assert resolution.thread_resolution_method == "new_thread"
+
+
+def test_changed_subject_with_valid_reply_headers():
+    thread_id = ObjectId()
+    parent = _known("<a@gentic.email>", thread_id)
+    known = {parent.internet_message_id: parent}
+    resolution = resolve_thread_from_known(
+        account_id="acct-1",
+        in_reply_to="<a@gentic.email>",
+        references=[],
+        subject="Completely changed subject",
+        participants={"rahul@example.com"},
+        known_by_internet_id=known,
+    )
+    assert resolution.thread_id == thread_id
+
+
+def test_cross_tenant_message_is_ignored():
+    thread_id = ObjectId()
+    parent = _known("<a@gentic.email>", thread_id, account_id="other-acct")
+    known = {parent.internet_message_id: parent}
+    resolution = resolve_thread_from_known(
+        account_id="acct-1",
+        in_reply_to="<a@gentic.email>",
+        references=[],
+        subject="Re: Project update",
+        participants={"rahul@example.com"},
+        known_by_internet_id=known,
+    )
+    assert resolution.thread_id is None
+
+
+def test_build_references_header_appends_parent():
+    header = build_references_header(["<a@gentic.email>"], "<b@example.com>")
+    assert header == "<a@gentic.email> <b@example.com>"
+
+
+def test_parse_message_id_list_handles_folded_references():
+    values = parse_message_id_list("<a@gentic.email>\r\n <b@example.com>")
+    assert values == ["<a@gentic.email>", "<b@example.com>"]