Python: Fix: Add system_instructions to ChatClient LLM span tracing

[claude89757]

Summary

• Fix LLM Span missing system messages when using instructions parameter in ChatOptions
• Add system_instructions parameter to _capture_messages() calls in _trace_get_response() and _trace_get_streaming_response()
• Add unit tests to verify the fix

Related Issue

Fixes #3163

Problem

When using ChatClient with ChatOptions.instructions, the OpenTelemetry LLM span is missing:

• System messages in gen_ai.input.messages
• The gen_ai.system_instructions attribute

The root cause is that _trace_get_response() and _trace_get_streaming_response() don't pass the system_instructions parameter to _capture_messages(), unlike the Agent-level tracing (_trace_agent_run()) which correctly does this.

Solution

Extract chat_options from kwargs and pass instructions to _capture_messages():

chat_options = kwargs.get("chat_options")
_capture_messages(
    span=span,
    provider_name=provider_name,
    messages=messages,
    system_instructions=getattr(chat_options, "instructions", None) if chat_options else None,
)

Test plan

• Add unit test for non-streaming ChatClient with instructions
• Add unit test for streaming ChatClient with instructions
• Add unit test to verify no system_instructions when not provided
• Run uv run poe fmt - formatting check passed
• Run uv run poe lint - all checks passed
• Run uv run --directory packages/core poe test - 1349 tests passed

🤖 Generated with Claude Code

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
observability.py	644	150	76%	244, 312–317, 319, 321–322, 324, 326–328, 331–333, 338–339, 345–346, 352–353, 360, 362–364, 367–369, 374–375, 381–382, 388–389, 396, 433, 436, 439–441, 444, 447–448, 451–453, 455–457, 460, 547, 549, 631, 649–650, 652, 655, 663–664, 667–670, 672, 675–677, 680–681, 694–700, 702–711, 714–718, 721–724, 726–729, 732–733, 741, 842, 844, 869–871, 993, 995, 999–1004, 1006, 1009–1013, 1015, 1293, 1373–1375, 1447–1449, 1622, 1630, 1634, 1638, 1644, 1646, 1648, 1656, 1666, 1724, 1726, 1733, 1749, 1752, 1812, 1828, 1832, 1966, 1968
TOTAL	17630	2881	83%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2622	154 💤	0 ❌	0 🔥	59.320s ⏱️