fix(ingest): retry on bibkey UNIQUE collision (audit C-15)

The id-keyed upsert (ON CONFLICT (id)) does not catch the papers.bibkey UNIQUE
constraint, so a second paper whose auto-generated key matches an existing one
(two same-author/year works → e.g. 'BobenkoLutz2023') failed the whole ingest
with a UniqueViolation. Surfaced by the canonical-id re-ingest: 2305.10988
collided with 2310.17529.

ingest now catches a bibkey UniqueViolation, rolls back, and retries the upsert
with an a/b/c… suffix. Non-bibkey violations re-raise unchanged. Mocks don't
raise, so the existing happy-path tests are untouched; a new test drives the
collision-and-retry path.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/ingest/test_ingest.py

@@ -11,6 +11,7 @@ from typing import Any
 from unittest.mock import MagicMock, patch
 
 import numpy as np
+import psycopg
 import pytest
 
 from codex.ingest import IngestResult, _make_bibkey, ingest_paper
@@ -525,6 +526,40 @@ def test_ingest_sets_bibkey_when_none(tmp_path: Any) -> None:
     assert upsert_params["bibkey"] == "AliceBob2023"
 
 
+def test_ingest_disambiguates_bibkey_on_unique_violation() -> None:
+    """A papers.bibkey UNIQUE collision is retried with an a/b/c suffix (audit C-15)."""
+    paper = _make_paper()  # bibkey auto-generates to "AliceBob2023"
+    mock_conn = MagicMock()
+    state = {"first": True}
+
+    def execute_side_effect(sql: str, params: Any = None) -> MagicMock:
+        # The first papers INSERT collides on the bibkey; the retry must succeed.
+        if "INSERT INTO papers" in sql and state["first"]:
+            state["first"] = False
+            raise psycopg.errors.UniqueViolation(
+                'duplicate key value violates unique constraint "papers_bibkey_key"'
+            )
+        return MagicMock()
+
+    mock_conn.execute.side_effect = execute_side_effect
+
+    with (
+        patch("codex.ingest.openalex.fetch_paper", return_value=paper),
+        patch("codex.ingest.openalex.fetch_citations", return_value=[]),
+        patch("codex.ingest.get_embedder", return_value=_fake_embedder()),
+        patch("codex.ingest.get_conn", side_effect=_make_conn_cm(mock_conn)),
+    ):
+        ingest_paper(paper.id)
+
+    papers_inserts = [
+        c for c in mock_conn.execute.call_args_list if "INSERT INTO papers" in c[0][0]
+    ]
+    assert len(papers_inserts) == 2, "expected one retry after the bibkey collision"
+    assert papers_inserts[0][0][1]["bibkey"] == "AliceBob2023"
+    assert papers_inserts[1][0][1]["bibkey"] == "AliceBob2023a"
+    mock_conn.rollback.assert_called_once()
+
+
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