Python: Add missing system instruction attr to invoke_agent span

[TaoChenOSU]

Motivation and Context

The system instruction attribute is silently dropped from the agent_invoke span, because we are using the wrong dictionary.

Description

Fix the bug by using the correct dictionary.

Previously:

After:

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

This PR fixes a bug in the observability instrumentation where system instructions from default_options were being silently dropped from the agent_invoke span. The fix corrects the code to use merged_options (which contains both default_options and runtime options) instead of options (which contains only runtime options) when extracting system instructions for telemetry.

Changes:

• Fixed system instruction extraction in telemetry to use merged options instead of runtime options only
• Added comprehensive test coverage for instruction merging scenarios in both streaming and non-streaming modes
• Updated observability sample to enable sensitive data to demonstrate the fix
• Added azure-ai-search to enforced coverage modules (housekeeping)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
python/packages/core/agent_framework/observability.py	Fixed two calls to _get_instructions_from_options to use merged_options instead of options
python/packages/core/tests/core/test_observability.py	Added comprehensive test coverage for instructions from default_options, runtime options, merged options, streaming modes, and edge cases
python/samples/02-agents/observability/agent_observability.py	Enabled sensitive data in observability configuration and improved comment formatting
.github/workflows/python-check-coverage.py	Added azure-ai-search to enforced coverage modules

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/anthropic/agent_framework_anthropic
_chat_client.py	372	35	90%	453, 540, 542, 666–667, 730, 751–752, 795–797, 799, 812–813, 820–822, 826–828, 832–835, 947, 957, 991, 1013, 1153–1154, 1171, 1184, 1197, 1222–1223
packages/core/agent_framework
observability.py	617	80	87%	346, 348–350, 353–355, 360–361, 367–368, 374–375, 382, 384–386, 389–391, 396–397, 403–404, 410–411, 418, 687, 690, 698–699, 702–705, 707, 710–712, 715–716, 744, 746, 757–759, 761–763, 767, 775, 876, 878, 1027, 1029, 1033–1038, 1040, 1043–1047, 1049, 1158–1159, 1161, 1218–1219, 1354, 1524, 1527, 1586, 1756, 1910, 1912
TOTAL	20606	3115	84%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
4013	225 💤	0 ❌	0 🔥	1m 9s ⏱️