From 15880bf41c2fdb312c8ac336b27007803dd89fe8 Mon Sep 17 00:00:00 2001
From: Ashen <310210685+ashen0x@users.noreply.github.com>
Date: Fri, 2 Oct 2026 01:59:46 +0530
Subject: [PATCH] fix: skip deeply nested upstream events in the stats observer

---
 routstr/upstream/terminal_outcome_tracking.py     | 5 +++--
 tests/unit/test_streaming_billing_finalization.py | 8 ++++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/routstr/upstream/terminal_outcome_tracking.py b/routstr/upstream/terminal_outcome_tracking.py
index 69daba20..dd3482cb 100644
--- a/routstr/upstream/terminal_outcome_tracking.py
+++ b/routstr/upstream/terminal_outcome_tracking.py
@@ -160,8 +160,9 @@ def observe_terminal_sse_bytes(
             continue
         try:
             parsed = json.loads(payload)
-        except ValueError:
-            # Bytes cut inside a character raise UnicodeDecodeError, not JSONDecodeError.
+        except (ValueError, RecursionError):
+            # Bytes cut inside a character raise UnicodeDecodeError, not
+            # JSONDecodeError; an upstream's deep nesting raises RecursionError.
             continue
         if isinstance(parsed, dict):
             state.observe(parsed)
diff --git a/tests/unit/test_streaming_billing_finalization.py b/tests/unit/test_streaming_billing_finalization.py
index 140183f2..194af2f5 100644
--- a/tests/unit/test_streaming_billing_finalization.py
+++ b/tests/unit/test_streaming_billing_finalization.py
@@ -1388,6 +1388,14 @@ def test_stream_cut_inside_a_character_does_not_raise() -> None:
     assert observe_terminal_sse_bytes(state, b"", tail, final=True) == b""
 
 
+def test_deeply_nested_event_does_not_raise() -> None:
+    state = TerminalOutcomeState()
+    event = b"data: " + b"[" * 200_000 + b"]" * 200_000 + b"\n\n"
+
+    assert observe_terminal_sse_bytes(state, b"", event, final=True) == b""
+    assert state.usage is None
+
+
 def test_routstr_upstream_cost_event_is_not_provider_usage() -> None:
     state = TerminalOutcomeState()
     stream = (