Account for Copilot reasoning tokens in usage details

[PratikDhanave (PratikDhanave)]

When converting a Copilot assistant.usage event, assistantUsageUpdate mapped input, output, total, and cache-read tokens but never read AssistantUsageData.ReasoningTokens:

details := message.UsageDetails{
    InputTokenCount:       inputTokens,
    OutputTokenCount:      outputTokens,
    TotalTokenCount:       inputTokens + outputTokens,
    CachedInputTokenCount: int64Value(data.CacheReadTokens),
    AdditionalCounts:      additionalUsageCounts(data),
}

The SDK documents ReasoningTokens as "Number of output tokens used for reasoning (e.g., chain-of-thought)." For a reasoning model those tokens were silently dropped: the framework’s dedicated UsageDetails.ReasoningTokenCount field (populated by the OpenAI and Gemini providers, summed by UsageDetails.Add) stayed 0, so callers had no reasoning-token breakdown from Copilot.

Fix

    CachedInputTokenCount: int64Value(data.CacheReadTokens),
    ReasoningTokenCount:   int64Value(data.ReasoningTokens),

ReasoningTokens is a subset of the output tokens, so TotalTokenCount (input + output) already accounts for it and is left unchanged — only the missing breakdown field is added, consistent with the OpenAI providers.

Test

TestConvertToAgentResponseUpdate_UsageEvent_SurfacesReasoningTokens drives an assistant.usage event with reasoningTokens: 8 and asserts ReasoningTokenCount == 8. It fails on the old code (0) and passes with the fix.

[Copilot]

Pull request overview

This PR updates the Copilot provider’s assistant.usage event conversion to preserve the reasoning-token breakdown by mapping AssistantUsageData.ReasoningTokens into the framework’s UsageDetails.ReasoningTokenCount, matching the behavior of other providers (e.g., OpenAI).

Changes:

• Populate UsageDetails.ReasoningTokenCount from Copilot reasoningTokens when converting assistant.usage events.
• Add a unit test ensuring reasoning tokens are surfaced in the resulting UsageContent details.

Reviewed changes

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

File	Description
provider/copilotprovider/copilot.go	Maps Copilot ReasoningTokens into UsageDetails.ReasoningTokenCount during usage-event conversion.
provider/copilotprovider/copilot_test.go	Adds a regression test asserting reasoningTokens is preserved in UsageDetails.

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