[dotnet-code] Cache agent mode display internals

[Michelle Clayton (michelle-clayton-work)]

Summary

Cache the agent-mode provider's supported-mode display string during construction instead of rebuilding it each time tools are created. This mirrors the .NET provider's stored mode-name display field and keeps future .NET-to-Go ports structurally easier to compare without changing public APIs or behavior.

.NET Reference

• dotnet/src/Microsoft.Agents.AI/Harness/AgentMode/AgentModeProvider.cs - stores _modeNamesDisplay during provider construction and reuses it in tool descriptions and validation errors.

Public API and Behavior

No public Go API changed. No intentional behavior change was made.

Tests

• go test ./agent/harness/agentmode

Notes

Rejected candidates:

• dotnet/src/Microsoft.Agents.AI.Abstractions/AgentSessionStateBagValue.cs overlapped with the existing open PR [dotnet-code] Consolidate portable value delayed decode helper #900.
• dotnet/src/Microsoft.Agents.AI.Workflows/HandoffToolCallFilteringBehavior.cs has no matching Go implementation; adding it would be a feature.
• dotnet/src/Microsoft.Agents.AI.Workflows/Configured.cs did not expose a similarly small, behavior-preserving Go cleanup after comparison with workflow executor internals.

Generated by .NET-to-Go Code Portability Refactoring Agent · gpt55 · 78.8 AIC · ⌖ 15.8 AIC · ⊞ 23.2K · ◷

Closes #911

[Copilot]

Pull request overview

Caches the agent-mode provider’s supported-modes display string at construction time so tool descriptions and validation errors reuse a prebuilt value, aligning the Go provider’s internal structure more closely with the referenced .NET implementation without changing public APIs.

Changes:

• Build and store modeNamesDisplay once in New(...) instead of rebuilding it inside createTools(...).
• Add a modeNamesDisplay field to Provider and use it in tool descriptions and invalid-mode error formatting.

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[github-actions]

Go API Consistency Review

Scope: internal-only
Changed Go contract: None — only unexported field modeNamesDisplay added to Provider struct in agent/harness/agentmode/agentmode.go
Upstream evidence reviewed: dotnet/src/Microsoft.Agents.AI/Harness/AgentMode/AgentModeProvider.cs — _modeNamesDisplay private field cached during construction and reused in mode_set tool description and validation error message
Result: aligned

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This PR caches the mode-names display string at construction time instead of recomputing it on every createTools call. The change is a pure internal refactor:

• No exported Go APIs changed.
• Observable behavior is identical — callers see the same tool description and error message strings.
• The structural pattern directly mirrors the upstream .NET AgentModeProvider._modeNamesDisplay private field referenced in the PR description.

No parity issues found. The parity-approved label has been added.

Generated by Go API Consistency Review Agent for #927 · sonnet46 · 20.3 AIC · ⌖ 4.06 AIC · ⊞ 6.4K · ◷