From 050ebd65f7225af2cb1e557ed2fc8df4d47fd962 Mon Sep 17 00:00:00 2001
From: Anish Gurjar <50738829+anishgurjar@users.noreply.github.com>
Date: Tue, 20 Oct 2026 14:14:31 -0400
Subject: [PATCH 1/4] fix(langchain): deregister langfuse prompts when a chain
 run errors

---
 langfuse/langchain/CallbackHandler.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/langfuse/langchain/CallbackHandler.py b/langfuse/langchain/CallbackHandler.py
index 65ce1b2d8..0db58cd6e 100644
--- a/langfuse/langchain/CallbackHandler.py
+++ b/langfuse/langchain/CallbackHandler.py
@@ -852,6 +852,8 @@ def on_chain_error(
         except Exception as e:
             langfuse_logger.exception(e)
         finally:
+            self._deregister_langfuse_prompt(run_id)
+
             if parent_run_id is None:
                 self._exit_propagation_context(run_id)
                 self._reset(run_id)

From 377e95e82b63f3dc22ce9d853ffee74afe42a86f Mon Sep 17 00:00:00 2001
From: Anish Gurjar <50738829+anishgurjar@users.noreply.github.com>
Date: Tue, 20 Oct 2026 14:15:10 -0400
Subject: [PATCH 2/4] test(langchain): cover prompt deregistration on chain
 error

---
 tests/unit/test_langchain.py | 76 ++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/tests/unit/test_langchain.py b/tests/unit/test_langchain.py
index dbbb3d93b..6b6143fcc 100644
--- a/tests/unit/test_langchain.py
+++ b/tests/unit/test_langchain.py
@@ -401,6 +401,82 @@ def test_streamed_llm_error_cleans_only_its_completion_start_time_memo(
         )
 
 
+def test_chain_error_deregisters_prompt_registered_for_the_run(
+    langfuse_memory_client,
+):
+    handler = CallbackHandler()
+
+    root_run_id = uuid4()
+    prompt_chain_run_id = uuid4()
+
+    handler.on_chain_start(
+        {"name": "RootChain"},
+        {"input": "hi"},
+        run_id=root_run_id,
+    )
+    handler.on_chain_start(
+        {"name": "PromptChain"},
+        {"input": "hi"},
+        run_id=prompt_chain_run_id,
+        parent_run_id=root_run_id,
+        metadata={"langfuse_prompt": "sentinel-prompt"},
+    )
+
+    assert handler._prompt_to_parent_run_map.get(root_run_id) == "sentinel-prompt"
+
+    handler.on_chain_error(
+        RuntimeError("synthetic failure"),
+        run_id=root_run_id,
+    )
+
+    assert root_run_id not in handler._prompt_to_parent_run_map
+
+
+def test_nested_chain_error_deregisters_propagated_prompt(
+    langfuse_memory_client,
+):
+    handler = CallbackHandler()
+
+    root_run_id = uuid4()
+    prompt_chain_run_id = uuid4()
+    nested_chain_run_id = uuid4()
+
+    handler.on_chain_start(
+        {"name": "RootChain"},
+        {"input": "hi"},
+        run_id=root_run_id,
+    )
+    handler.on_chain_start(
+        {"name": "PromptChain"},
+        {"input": "hi"},
+        run_id=prompt_chain_run_id,
+        parent_run_id=root_run_id,
+        metadata={"langfuse_prompt": "sentinel-prompt"},
+    )
+    handler.on_chain_start(
+        {"name": "NestedChain"},
+        {"input": "hi"},
+        run_id=nested_chain_run_id,
+        parent_run_id=root_run_id,
+    )
+
+    assert (
+        handler._prompt_to_parent_run_map.get(nested_chain_run_id) == "sentinel-prompt"
+    )
+
+    handler.on_chain_error(
+        RuntimeError("synthetic failure"),
+        run_id=nested_chain_run_id,
+        parent_run_id=root_run_id,
+    )
+
+    assert nested_chain_run_id not in handler._prompt_to_parent_run_map
+
+    # The parent-level registration survives so a following LLM sibling
+    # can still consume it, matching the success-path lifecycle.
+    assert handler._prompt_to_parent_run_map.get(root_run_id) == "sentinel-prompt"
+
+
 def test_control_flow_resume_uses_thread_keyed_explicit_resume_context(
     memory_exporter, langfuse_memory_client, monkeypatch
 ):

From 12180f32c91f65f74664bebda6769cd5aded986f Mon Sep 17 00:00:00 2001
From: Anish Gurjar <50738829+anishgurjar@users.noreply.github.com>
Date: Tue, 20 Oct 2026 14:16:22 -0400
Subject: [PATCH 3/4] style: trim trailing blank line for ruff format


From 3ab821ccff7d81cf739b18a818ce3b4cfc9db3c3 Mon Sep 17 00:00:00 2001
From: Anish Gurjar <50738829+anishgurjar@users.noreply.github.com>
Date: Tue, 20 Oct 2026 14:17:14 -0400
Subject: [PATCH 4/4] style: trim trailing blank line for ruff format