Python: Fix spurious Magentic custom manager warning

[moonbox3]

Motivation and Context

Fixes #4306.

MagenticBuilder logged Custom manager provided; all other manager arguments will be ignored. whenever a custom manager or manager_factory was supplied, even when the caller did not pass any standard-manager options. This happened because max_stall_count defaulted to 3, so the warning check could not distinguish an omitted value from an explicit override.

Description

Updates MagenticBuilder to use the existing _MISSING sentinel for max_stall_count so omitted values remain distinguishable from explicitly supplied values. The builder resolves omitted max_stall_count to 3 only when constructing a StandardMagenticManager.

Adds regression coverage for custom manager and manager factory configurations that should not warn, preserves the warning when a standard-manager option is explicitly supplied with a custom manager, and verifies manager_agent_factory still receives the default max_stall_count.

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.

[github-actions]

Automated Code Review

Reviewers: 4 | Confidence: 94% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Design Approach

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Automated review by moonbox3's agents

[Copilot]

Pull request overview

This PR fixes a misleading warning in the Python orchestration MagenticBuilder where supplying a custom manager/manager_factory always triggered “Custom manager provided; all other manager arguments will be ignored.” due to max_stall_count having a non-sentinel default. It makes omitted max_stall_count distinguishable from an explicit override, and adds regression tests around the warning behavior and default resolution.

Changes:

• Update MagenticBuilder / _set_manager to use the existing _MISSING sentinel for max_stall_count, resolving it to 3 only when constructing StandardMagenticManager.
• Adjust the warning condition so it only fires when standard-manager options were actually provided alongside a custom manager.
• Add tests to verify (1) no warning for custom manager/manager_factory without standard options, (2) warning still occurs when a standard option is explicitly set, and (3) manager_agent_factory still uses the default max_stall_count=3.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
python/uv.lock	Updates locked dependencies (notably azure-ai-agentserver-responses to 1.0.0b7 and related transitive additions) consistent with current workspace requirements.
python/packages/orchestrations/tests/test_magentic.py	Adds regression tests covering the warning behavior and default max_stall_count resolution for agent factory builds.
python/packages/orchestrations/agent_framework_orchestrations/_magentic.py	Introduces _MISSING sentinel handling for max_stall_count and refines warning logic; resolves default only when instantiating StandardMagenticManager.

[github-actions]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/bedrock/agent_framework_bedrock
_chat_client.py	445	98	77%	304–305, 321–330, 336, 404, 413, 424, 426, 428, 433, 452–453, 477, 490, 502, 505, 513–514, 517–518, 520–521, 526–528, 530, 540–541, 563, 570, 579–580, 582–583, 585–587, 589, 591–592, 598–600, 603–604, 610–613, 619–629, 632, 651, 656, 701–702, 715, 741, 753, 758, 786, 790–791, 794, 812, 836, 848, 852, 866, 874–875, 879, 881–888
packages/orchestrations/agent_framework_orchestrations
_concurrent.py	147	24	83%	59, 68–69, 97–98, 103, 121, 126, 131–132, 153, 163, 170, 244, 260, 263, 320, 350, 352–353, 355, 360, 373, 377
_group_chat.py	332	70	78%	183, 352, 359, 392, 403–404, 410, 415, 436, 440, 453–454, 467, 482–483, 485, 501, 528–533, 535, 569–572, 574, 579–583, 677, 680, 719, 722, 725, 728, 736, 748–749, 751–752, 754–755, 757, 762, 765, 774, 780, 824–825, 829–830, 844–845, 847–848, 879–880, 946, 965, 973, 978–980, 987, 997
_handoff.py	339	52	84%	112–113, 115, 168–178, 180, 182, 184, 189, 320, 345, 372, 398, 462, 505, 513, 517–518, 549–551, 556–558, 688, 691, 704, 766, 771, 778, 788, 790, 809, 811, 893–894, 926–927, 1039, 1046, 1118–1119, 1121
_magentic.py	596	91	84%	73–82, 87, 91–102, 267, 278, 282, 302, 363, 372, 374, 416, 433, 442–443, 445–447, 449, 460, 603, 605, 645, 695, 731–733, 735, 745, 753–754, 821–824, 915, 921, 927, 969, 1007, 1039, 1056, 1067, 1124–1125, 1129–1131, 1155, 1179–1180, 1193, 1213, 1236, 1281–1282, 1320–1321, 1490, 1493, 1502, 1505, 1510, 1561–1562, 1603–1604, 1652, 1683, 1741, 1755, 1766
_participant_output_config.py	85	6	92%	35, 41, 53, 56, 112, 166
_sequential.py	83	6	92%	56, 132, 143, 149, 197, 225
TOTAL	37783	4420	88%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
7512	34 💤	0 ❌	0 🔥	2m 0s ⏱️

[eavanvalkenburg]

Do we need this cast?