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Remove trailing system→user conversion for cross-call stability

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Perplexity appears to have statefulness within a conversation, so
converting a system message to "user" in one call and then back to
"system" in the next (after more messages are appended) causes API
errors. Remove the trailing system→user conversion entirely — if the
context only has system messages, the API call will fail but the
mistake will be caught right away.
This commit is contained in:
Paul Kompfner
2026-03-12 16:04:46 -04:00
parent e69f5a76e1
commit 99f28120b7
2 changed files with 31 additions and 42 deletions
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41
tests/test_get_llm_invocation_params.py
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@@ -1123,8 +1123,14 @@ class TestPerplexityGetLLMInvocationParams(unittest.TestCase):
self.assertEqual(params["messages"][0]["role"], "user")
self.assertEqual(params["messages"][0]["content"], "Hello")
def test_only_system_message_converted_to_user(self):
"""Test that a single system message is converted to user role."""
def test_only_system_messages_preserved(self):
"""Test that system-only contexts are left unchanged (no system→user conversion).
We intentionally do not convert trailing system messages to "user"
because that would make the transformation unstable across calls —
Perplexity has statefulness within a conversation, so a message that
was "user" in one call but becomes "system" in the next causes errors.
"""
messages: list[LLMStandardMessage] = [
{"role": "system", "content": "You are a helpful assistant."},
]
@@ -1133,30 +1139,15 @@ class TestPerplexityGetLLMInvocationParams(unittest.TestCase):
params = self.adapter.get_llm_invocation_params(context)
self.assertEqual(len(params["messages"]), 1)
self.assertEqual(params["messages"][0]["role"], "user")
self.assertEqual(params["messages"][0]["content"], "You are a helpful assistant.")
def test_only_system_messages_last_converted_to_user(self):
"""Test that when only system messages exist, the last one is converted to user."""
messages: list[LLMStandardMessage] = [
{"role": "system", "content": "You are a helpful assistant."},
{"role": "system", "content": "Always be polite."},
]
context = LLMContext(messages=messages)
params = self.adapter.get_llm_invocation_params(context)
self.assertEqual(len(params["messages"]), 2)
self.assertEqual(params["messages"][0]["role"], "system")
self.assertEqual(params["messages"][0]["content"], "You are a helpful assistant.")
self.assertEqual(params["messages"][1]["role"], "user")
self.assertEqual(params["messages"][1]["content"], "Always be polite.")
def test_trailing_assistant_removed_then_system_converted(self):
"""Test that trailing assistant is removed, exposing a system message that becomes user.
def test_system_exposed_after_trailing_assistant_removed(self):
"""Test that a system message exposed by trailing assistant removal stays system.
This exercises the ordering of step 3: strip trailing assistants first,
then convert a trailing system to user.
It's important that initial system messages are never converted to
"user", because Perplexity has statefulness within a conversation — if
a message was sent as "system" in one call and then becomes "user" in a
later call (after more messages are appended), the API rejects it.
"""
messages: list[LLMStandardMessage] = [
{"role": "system", "content": "You are helpful."},
@@ -1166,9 +1157,9 @@ class TestPerplexityGetLLMInvocationParams(unittest.TestCase):
context = LLMContext(messages=messages)
params = self.adapter.get_llm_invocation_params(context)
# Trailing assistant removed → [system] → system converted to user → [user]
# Trailing assistant removed → [system], system stays as-is
self.assertEqual(len(params["messages"]), 1)
self.assertEqual(params["messages"][0]["role"], "user")
self.assertEqual(params["messages"][0]["role"], "system")
self.assertEqual(params["messages"][0]["content"], "You are helpful.")
def test_consecutive_assistants_merged_then_trailing_removed(self):