From 83e2027e2a6730e6cb749bad5776c31fa98e642f Mon Sep 17 00:00:00 2001
From: mottopanikeiku <176798723+mottopanikeiku@users.noreply.github.com>
Date: Thu, 22 Oct 2026 04:52:21 -0700
Subject: [PATCH] fix(nemotron3): render later system messages instead of
 raising

The Nemotron 3 chat templates render a system message that is not first as its own system turn, and bridge_to_next_turn already does the same, but render() raised ValueError. I render it through the user branch like the template does and run the later-system parity scenario for the Nemotron renderers.

Assisted-by: Claude
Assisted-by: GPT-6 Astra
Signed-off-by: mottopanikeiku <176798723+mottopanikeiku@users.noreply.github.com>
---
 renderers/nemotron3.py | 10 +++++-----
 tests/parity.py        |  8 +++++++-
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/renderers/nemotron3.py b/renderers/nemotron3.py
index 53276ed25..e3b372862 100644
--- a/renderers/nemotron3.py
+++ b/renderers/nemotron3.py
@@ -428,16 +428,16 @@ def emit_text_segments(
             content = self._render_content(msg.get("content"))
             msg_orig_idx = orig_idx(i)
 
-            if role == "system":
-                if i != 0:
-                    raise ValueError("System message must be at the beginning.")
+            if role == "system" and i == 0:
                 continue  # Already handled above
 
-            elif role == "user":
+            elif role in ("user", "system"):
+                # The template renders a later system message through the
+                # user branch, under its own role header.
                 emit_special(
                     self._im_start, msg_orig_idx, is_sampled=False, is_content=False
                 )
-                user_segments: list[tuple[str, bool]] = [("user\n", False)]
+                user_segments: list[tuple[str, bool]] = [(f"{role}\n", False)]
                 if content:
                     user_segments.append((content, True))
                 # Reasoning-effort hint rides on the LAST user message only,
diff --git a/tests/parity.py b/tests/parity.py
index ac34e11cc..2b75fb493 100644
--- a/tests/parity.py
+++ b/tests/parity.py
@@ -660,7 +660,13 @@ def _call(city: str, *, id: str | None = None) -> dict:
             {"role": "system", "content": "Late instruction"},
             {"role": "user", "content": "B"},
         ],
-        only_renderers={"laguna-xs-2.1", "laguna-s-2.1"},
+        only_renderers={
+            "laguna-xs-2.1",
+            "laguna-s-2.1",
+            "nemotron-3",
+            "nemotron-3-ultra",
+            "nemotron-3.5",
+        },
     ),
     _scenario(
         "tool-declare-message",