* fix(chat_templates): bind loop_messages when default_system_message is None
construct_chat_template(default_system_message=None) built a system part that
binds loop_messages only inside the `{% if messages[0]['role'] == 'system' %}`
arm. The `Fix missing loop_messages` step right below then found no
unconditional `{% set loop_messages = messages %}`, concluded loop_messages was
missing, and rewrote `{% for message in loop_messages %}` back to
`{% for message in messages %}` -- undoing the `messages[1:]` skip.
A caller-supplied system message therefore reached the loop and tripped
raise_exception:
Only user and assistant roles are supported!
Add the `{% else %}` arm so loop_messages is always bound, mirroring the
default_system_message is not None branch minus the default text. That also
stops the rewrite from firing, since the unconditional binding is now present.
Renders before / after, same template, same inputs:
default_system_message input before after
None system msg raise_exception 'Be terse.\n### User: Hi\n'
None no system '### User: Hi\n' unchanged
'You are helpful.' system msg 'Be terse.\n### User: Hi\n' unchanged
'You are helpful.' no system 'You are helpful.\n...' unchanged
The rewrite still fires for templates with no {SYSTEM} part, which is what it
was there for -- verified unchanged.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
* Scope loop_messages binding to {SYSTEM} templates for PR #7199
The None branch now only adds the else arm when system_part contains
{SYSTEM}, so a static prefix with no {SYSTEM} placeholder keeps raising on a
caller system message instead of silently dropping it. Strengthen the tests:
assert the default does not leak when a caller system message is present, and
add a regression test for the static prefix case.
---------
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: danielhanchen <danielhanchen@gmail.com>
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