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 SDK telemetry API changes with preserved backward compatibility; behavior shifts only for TrackMetricsOf when the metrics extractor throws (no longer records generation error).

Overview
Brings the .NET server AI tracker in line with JS/Python/Java by extending AiMetrics and MetricSummary, and tightening TrackMetricsOf behavior.

AiMetrics gains optional ToolCalls and DurationMs (existing two-arg constructor stays valid). TrackMetricsOf now emits tool-call events from ToolCalls, uses DurationMs when set (otherwise stopwatch time captured before the extractor runs), and splits failures: operation exceptions record duration + error; extractor exceptions record duration only and rethrow.

MetricSummary adds ToolCalls (accumulated from TrackToolCall, lock-protected) and ResumptionToken. TrackToolCall appends each key to that list while keeping per-call $ld:ai:tool_call tracking unchanged.

Nine new unit tests cover backward compatibility, overrides, extractor semantics, and summary fields.

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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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