HermesA2AExecutor now supports sending system context as ordered, separate
role=system messages instead of a single concatenated string — the model
format recommended by NousResearch.
Changes:
- HermesA2AExecutor.__init__: new system_blocks kwarg (list[str|None]|None)
stored as an independent copy; None blocks and empty strings silently skipped
- _build_messages(): when system_blocks is not None, emits each non-empty
block as a separate {"role": "system"} entry in Hermes-recommended order
(persona → tools context → reasoning policy); falls through to legacy
system_prompt path when system_blocks is None (backward compatible)
Backward compatibility: existing callers that pass a single system_prompt
string continue to work identically — no changes required.
Tests (12 new, 47 total):
- system_blocks stored as independent copy (mutation safe)
- three-block stacked ordering preserved
- empty / None blocks silently skipped
- all-empty list → zero system messages
- system_blocks overrides system_prompt when both provided
- legacy system_prompt path unchanged
- stacked blocks appear in the live API call kwargs
Closes#499
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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