fix(proxy): preserve original transport error if reconnect itself raises

Greptile review on #26756 (P2): if `attempt_db_reconnect` itself raises
(e.g. lock cancellation, timer error, unexpected internal failure), the
original `httpx.ReadError` / transport error was lost — `failure_handler`
and `db_exceptions` alerts then logged the reconnect exception instead of
the actual DB transport problem, masking the root cause.

Wrap the reconnect call in a try/except. On reconnect failure, re-raise
the *original* `first_exc` and chain the reconnect error as `__cause__`
so it remains visible for debuggability without becoming the primary
exception observers see.

Adds `test_call_with_db_reconnect_retry_preserves_original_error_when_reconnect_raises`
asserting (a) the propagated exception is the original transport error
and (b) the reconnect exception is attached as `__cause__`.

litellm/proxy/db/exception_handler.py

@@ -232,11 +232,26 @@ async def call_with_db_reconnect_retry(
             first_exc,
         )
 
-        did_reconnect = await prisma_client.attempt_db_reconnect(
-            reason=reason,
-            timeout_seconds=resolved_timeout,
-            lock_timeout_seconds=resolved_lock_timeout,
-        )
+        # Preserve the original transport error in telemetry. If
+        # `attempt_db_reconnect` itself raises (e.g. lock cancellation, timer
+        # error, unexpected internal failure), surfacing that exception
+        # instead of `first_exc` would mask the actual DB transport problem
+        # in `failure_handler` / `db_exceptions` alerts. Chain the reconnect
+        # error as the cause for debuggability without losing the original.
+        try:
+            did_reconnect = await prisma_client.attempt_db_reconnect(
+                reason=reason,
+                timeout_seconds=resolved_timeout,
+                lock_timeout_seconds=resolved_lock_timeout,
+            )
+        except Exception as reconnect_exc:
+            verbose_proxy_logger.warning(
+                "DB reconnect attempt raised; preserving original transport error. "
+                "reason=%s reconnect_error=%s",
+                reason,
+                reconnect_exc,
+            )
+            raise first_exc from reconnect_exc
         if not did_reconnect:
             raise
 

tests/test_litellm/proxy/db/test_exception_handler_reconnect_retry.py

@@ -223,3 +223,33 @@ async def test_call_with_db_reconnect_retry_uses_auth_defaults_when_unset():
     call_kwargs = client.attempt_db_reconnect.await_args.kwargs
     assert call_kwargs["timeout_seconds"] == 3.0
     assert call_kwargs["lock_timeout_seconds"] == 0.5
+
+
+@pytest.mark.asyncio
+async def test_call_with_db_reconnect_retry_preserves_original_error_when_reconnect_raises():
+    """If `attempt_db_reconnect` itself raises (lock cancellation, timer
+    error, unexpected internal failure), the helper must surface the
+    *original* transport error to telemetry — not the reconnect exception.
+    Otherwise `failure_handler` / `db_exceptions` alerts log the wrong
+    error string and the actual DB transport problem becomes invisible.
+
+    The reconnect error is chained as the `__cause__` for debuggability."""
+    client = MagicMock()
+    reconnect_exc = RuntimeError("simulated reconnect lock cancellation")
+    client.attempt_db_reconnect = AsyncMock(side_effect=reconnect_exc)
+    client._db_auth_reconnect_timeout_seconds = 2.0
+    client._db_auth_reconnect_lock_timeout_seconds = 0.1
+
+    original_exc = httpx.ReadError("transport blip")
+
+    async def _factory():
+        raise original_exc
+
+    with pytest.raises(httpx.ReadError) as exc_info:
+        await call_with_db_reconnect_retry(
+            client, _factory, reason="reconnect_itself_raises"
+        )
+
+    assert exc_info.value is original_exc
+    assert exc_info.value.__cause__ is reconnect_exc
+    client.attempt_db_reconnect.assert_awaited_once()