Python: Display system prompt in langfuse

[SuperKenVery]

Motivation and Context

Currently, using agent framework with langfuse, the system prompt wouldn't be shown with other user/agent messages, but as a tiny metadata:

Description

I made agent framework add a ChatMessage with its role set to "system" when capturing messages. Therefore, it shows (pretty-rendered markdown) together with user and assistant messages:

Closes #2507

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.

[SuperKenVery]

@microsoft-github-policy-service agree

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_types.py	952	102	89%	130–131, 149–150, 287, 289, 296, 315, 355, 401–402, 438, 588, 702–703, 705, 730, 737, 754–756, 829, 834–835, 837, 844–845, 847, 869, 876, 879–881, 886–887, 893–895, 1019, 1106–1109, 1117–1118, 1209, 1390, 1396, 1640–1642, 1648–1649, 1819, 1950, 1955, 1959, 1963, 2141–2143, 2155, 2206–2210, 2220, 2225, 2684, 2770–2772, 2845, 2856–2857, 3031, 3035, 3047–3049, 3150–3152, 3154–3156, 3159, 3163, 3166, 3171, 3216–3217, 3224–3225, 3259–3261, 3276, 3292, 3320, 3327
observability.py	609	101	83%	238, 264–266, 268, 270–274, 282–283, 288–289, 294–299, 322–324, 326–327, 333, 417, 427, 449, 455, 474–476, 484–486, 508–510, 520–522, 655, 657, 744–748, 751–755, 764–767, 777–780, 782, 1049, 1127–1129, 1199–1201, 1359, 1367, 1371, 1375, 1381, 1383, 1385, 1393, 1403, 1431–1432, 1445–1448, 1467–1469, 1471–1474, 1476–1477, 1481, 1484, 1542, 1558, 1562, 1696, 1698
TOTAL	16221	2540	84%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2319	130 💤	0 ❌	0 🔥	56.017s ⏱️

[eavanvalkenburg]

Thanks!