feat: extend AiMetrics, MetricSummary, and TrackMetricsOf

[mattrmc1]

Summary

Extends AiMetrics, MetricSummary, and TrackMetricsOf to bring the .NET AI SDK to spec parity with JS, Python, and Java for metric tracking. Addresses AIC-2727.

AiMetrics — new optional fields

public AiMetrics(bool success, Usage? tokens = null,
    IReadOnlyList<string> toolCalls = null, double? durationMs = null)

ToolCalls carries tool keys invoked during the operation (AIRUNNER §1.5.1). DurationMs provides an explicit duration override — when set, TrackMetricsOf uses it instead of the stopwatch measurement (AITRACK §1.1.13.2).

MetricSummary — new optional fields

public record struct MetricSummary(
    double? DurationMs,
    Feedback? Feedback,
    Usage? Tokens,
    bool? Success,
    double? TimeToFirstTokenMs,
    IReadOnlyList<string> ToolCalls = null,      // NEW
    string ResumptionToken = null                 // NEW
);

ToolCalls accumulates keys from TrackToolCall invocations. ResumptionToken surfaces the tracker's resumption token on the summary (AITRACK §1.1.17.2).

TrackMetricsOf — tool call auto-tracking & duration override

TrackMetricsOf now extracts ToolCalls from AiMetrics and calls TrackToolCalls automatically. It also honors DurationMs when present, falling back to the stopwatch value when null.

The error-handling semantics now match Java: if the operation throws, duration + error are tracked and the exception propagates. If the metrics extractor throws, duration is tracked but error is NOT — the AI operation itself succeeded.

TrackToolCall — accumulates keys on summary

TrackToolCall now appends to an internal list (lock-guarded) so that Summary.ToolCalls reflects all tool invocations. The existing per-call $ld:ai:tool_call event emission is unchanged.

How to test

dotnet test pkgs/sdk/server-ai/test/LaunchDarkly.ServerSdk.Ai.Tests.csproj --framework net8.0

9 new test cases covering backward compat, new field population, auto tool call tracking, duration override vs. stopwatch fallback, extractor failure semantics, and summary accumulation.

Known limitations

None. All changes are additive — existing constructors and call sites compile and behave identically.

---

Note

Low Risk
Additive API and observability behavior in the AI metrics SDK; the main behavioral change is clearer TrackMetricsOf error/duration semantics, which aligns with other language SDKs rather than changing security or data paths.

Overview
Brings the .NET server AI tracker in line with other SDKs by extending AiMetrics with optional ToolCalls and DurationMs, and MetricSummary with ToolCalls and ResumptionToken.

TrackMetricsOf now stops the timer before running the metrics extractor (so slow extractors do not inflate duration), uses DurationMs when provided, auto-emits tool-call events from AiMetrics.ToolCalls, and adjusts failure semantics: operation failures still record duration + generation error; extractor failures record duration only (no error), matching Java.

TrackToolCall appends keys to a lock-protected list so Summary.ToolCalls reflects all invocations; existing per-call $ld:ai:tool_call events are unchanged. Changes are additive for existing call sites; tests cover the new fields and behaviors.

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Summary ToolCalls live list alias

Medium Severity

Summary assigns ToolCalls from _toolCallKeys.AsReadOnly(), so the returned MetricSummary keeps a live view of the tracker’s internal list. Later TrackToolCall / TrackMetricsOf updates change a previously read summary’s tool list, and concurrent reads while tracking can throw during enumeration.

 

^{Triggered by learned rule: Tracker methods must defensive-copy caller-provided collections}

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