[dotnet-port-api] Add per-tool agent mode controls

[Michelle Clayton (michelle-clayton-work)]

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The original pull request description is below.

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Summary

Align agent/harness/agentmode with the .NET per-tool AgentModeProvider controls from microsoft/agent-framework#8458. This adds DisableModeSetTool and DisableModeGetTool config flags, keeps the default injected instructions coherent when either built-in tool is disabled, adds SetModeForSessionSilently for custom mode-switch flows that should not queue a follow-up notification, and extends the parity doc and package tests to cover the new behavior.

Ported .NET PRs

• .NET: Add per-tool AgentModeProvider controls agent-framework#8458 - Add per-tool AgentModeProvider controls
  • Upstream commit: dcd2c4d1e0b0fce6bcebe0f3d244351ba9002a80

Breaking Changes

No.

Tests and Examples

• go test ./agent/harness/agentmode
• go test ./agent/harness/...
• Added targeted coverage for per-tool disable combinations, default-instruction rewrites, and silent mode changes that clear pending notifications.
• No example changes.

Notes

• The local upstream-agent-framework/main fetch was blocked by the firewall in this environment, so upstream inspection used the GitHub read bridge against the merged .NET PR and commit instead of a refreshed local remote-tracking ref.
• Exact duplicate searches for [dotnet-port-api] plus the mode_set/mode_get AgentMode surface returned no matching workflow tracking issue before this port.

Closes #1097

[Copilot]

Copilot review overview

🔵 Needs a closer look

The built-in mode_set path can clear a queued PreviousMode notification, so the moderate finding must be addressed.

Review effort: Lite
Findings: None

What changed in this PR

Adds per-tool mode_set/mode_get controls and silent session mode changes to the Go agent-mode harness, with tests and .NET parity documentation.

Changes:

• Adds independent tool-disable controls and instruction rewriting.
• Adds silent mode updates that clear pending notifications.
• Expands tests and parity documentation.

File	Summary
docs/​dotnet-go-sdk-feature-comparison.md	Documents per-tool agent-mode parity.
agent/​harness/​agentmode/​agentmode.go	Implements controls and silent mode changes; the built-in mode_set path must preserve queued PreviousMode notifications.
agent/​harness/​agentmode/​agentmode_test.go	Adds coverage for tool combinations, instructions, and notification behavior.

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[github-actions]

Scope: public API, user-visible behavior

Changed Go contract: agent/harness/agentmode:

• New Config.DisableModeSetTool / Config.DisableModeGetTool fields (both default false).
• New exported Provider.SetModeForSessionSilently(session, mode) method.
• Behavior change: createTools conditionally omits mode_set/mode_get; buildInstructions conditionally strips {mode_get_instructions}/{mode_set_instructions}/{plan_mode_transition} guidance only when using default (non-custom) modes/instructions; SetModeForSession/SetModeForSessionSilently share setModeForSessionWithNotificationOption, which clears PreviousMode (pending notification) when silent.

Upstream evidence reviewed: dotnet/src/Microsoft.Agents.AI/Harness/AgentMode/AgentModeProvider.cs and AgentModeProviderOptions.cs from microsoft/agent-framework#8458 (merged commit dcd2c4d1e0b0fce6bcebe0f3d244351ba9002a80):

• AgentModeProviderOptions.DisableModeSetTool / DisableModeGetTool, both defaulting to false — matches Go's Config fields and zero-value defaults.
• CreateTools conditionally adds mode_set/mode_get via if (!this._disableModeSetTool) / if (!this._disableModeGetTool) — matches Go's createTools.
• BuildInstructions only rewrites {mode_get_instructions}/{mode_set_instructions}/{plan_mode_transition} when _usesDefaultInstructions/_usesDefaultModes, preserving custom instructions verbatim — matches Go's usesDefaultInstr/usesDefaultModes guards, and is covered by Options_DisabledTools_PreserveCustomInstructionsAsync (.NET) and TestCustomInstructions_AreNotRewrittenWhenModeToolsDisabled (Go).
• SetModeAsync(session, mode, disableNotification, ct) overload sets PreviousModeForNotification = null when disableNotification and otherwise preserves default (non-silent) notification behavior — matches Go's SetModeForSessionSilently clearing PreviousMode, and DisabledTools_PreserveStateInstructionsAndNotificationsAsync / PublicSetMode_DisableNotification_ClearsPendingNotificationAsync (.NET) map to TestSetModeForSessionSilently_ChangesModeWithoutNotification / TestSetModeForSessionSilently_ClearsPendingNotification (Go).

Result: aligned. The per-tool disable flags default to false (parity preserved for existing callers), the instruction-rewrite guarding for custom instructions/modes matches upstream exactly, and the silent-mode-set notification-suppression/clearing semantics mirror the .NET SetModeAsync overload. Naming is idiomatically Go (SetModeForSessionSilently vs. SetModeAsync(..., disableNotification: true, ...)) but conceptually equivalent. docs/dotnet-go-sdk-feature-comparison.md was updated to reference #8458. No parity issues found.

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