[NingLin Liu (ninglinLiu)]

Motivation & Context

AgentModeProvider validates the default mode and every SetModeAsync / mode_set call against the configured modes, but a mode restored from persisted session state is not validated. After an app removes or renames a mode, sessions saved before that change keep the old mode: GetModeAsync returns it, instructions mention it, and SetModeAsync would reject setting it again.

Description & Review Guide

• What are the major changes? GetModeAsync, ProvideAIContextAsync, and mode_get now run restored modes through EnsureConfiguredMode, which falls back to the configured default and persists the correction — matching Python get_agent_mode.
• What is the impact of these changes? Stale mode names from older configurations no longer stick after restore.
• What do you want reviewers to focus on? Parity with Python fallback and the new restore regression test.

Related Issue

Fixes #9829

AI Assistance

• No material AI assistance was used.
• This is an AI-assisted contribution. I reviewed, understood, and verified all submitted content and accept responsibility for it.

AI assistance details: Assisted with implementation and the restore regression test; I reviewed the change against Python get_agent_mode and the issue repro, and accept responsibility for the change.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR links to an agreed issue with no competing open PR, or the Related Issue section documents a trivial-change or repository-automation exception.
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

🟡 Changes recommended

Restoring the fallback mode leaves a pending notification marker intact, causing a spurious draft-to-draft mode-change notification on the next invocation; the marker must be cleared and the restore-and-invoke case tested.

1 open issue

• Clear stale mode notification marker during state restore · New

What changed in this PR

This PR addresses #9829 by making .NET AgentModeProvider fall back to the configured default when a restored session references a removed mode, matching Python behavior.

Changes:

• Validate restored modes in GetModeAsync, AI context generation, and mode_get.
• Persist the fallback mode in session state.
• Add a regression test for restoring a session after its mode is removed.

File	Description
dotnet/​tests/​Microsoft.Agents.AI.UnitTests/​Harness/​AgentMode/​AgentModeProviderTests.cs	Tests fallback after restoring an obsolete mode.
dotnet/​src/​Microsoft.Agents.AI/​Harness/​AgentMode/​AgentModeProvider.cs	Centralizes restored-mode validation and persists corrections.

_{Review effort: Balanced}

[westey (westey-m)]

Why call GetModeAsync twice and check it's output twice?

[NingLin Liu (ninglinLiu)]

Good catch — the second GetModeAsync is intentional: the first call is what performs the fallback and persists draft into session state, and the second call asserts that the rewritten mode sticks (so a later restore/read does not re-trigger fallback or flip back to the removed "review" id). Happy to collapse it to a single read + a StateBag assertion if you prefer that shape.

[Kartik Madan (kartikmadan11)]

this fixed my repro