Summary

Implements the full LDAIConfigTracker interface — previously a stub. Callers can now record AI operation metrics (duration, tokens, success/error, feedback, tool calls, judge results) with at-most-once enforcement, extract metrics from runner operations via trackMetricsOf, and reconstruct trackers across processes via resumption tokens.

Tracking methods

void trackDuration(Duration duration);
<T> T trackDurationOf(Callable<T> operation) throws Exception;

Records wall-clock duration. Null silently dropped (debug log); negatives clamped to zero. trackDurationOf wraps a Callable, measures via System.nanoTime(), records duration in finally even on exception.

<T> T trackMetricsOf(Function<? super T, AIMetrics> metricsExtractor, Callable<T> operation) throws Exception;

All-in-one wrapper: starts timer, invokes operation, stops clock before calling the extractor (slow extractors don't inflate duration). On success: prefers runner-reported durationMs over wall-clock, then delegates to trackSuccess/trackError, trackTokens, trackToolCalls. On exception: records wall-clock duration, calls trackError, rethrows. If the extractor itself throws, operation duration is still recorded before propagating — trackError is NOT called since the AI operation succeeded.

void trackSuccess();
void trackError();

Share a single AtomicReference<Boolean> guard — only the first to fire wins.

void trackFeedback(FeedbackKind kind);

Validates and resolves the event name before claiming the at-most-once guard, so null/invalid input doesn't burn the slot.

void trackTokens(TokenUsage tokens);

Emits events for each positive count (total, input, output). All-zero usage does not consume the at-most-once slot.

void trackToolCall(String toolKey);
void trackToolCalls(List<String> toolKeys);

Multi-fire (not at-most-once). Each call emits a separate $ld:ai:tool_call event.

void trackJudgeResult(JudgeResult result);

Silently dropped when not sampled, not successful, or when metricKey is blank/null or score is null/non-finite. Multi-fire.

void trackTimeToFirstToken(Duration duration);

Records time-to-first-token duration. At-most-once.

Resumption tokens

String getResumptionToken();                                            // on LDAIConfigTracker
LDAIConfigTracker createTracker(String resumptionToken, LDContext context); // on LDAIClient

getResumptionToken() returns URL-safe Base64 (no padding) JSON containing { runId, configKey, variationKey, version, graphKey }. variationKey and graphKey omitted when null. No length cap — large config keys are supported. Empty runId / configKey are rejected on decode.

Tracker factory wiring

LDAIClientImpl now creates real LDAIConfigTrackerImpl instances. A private trackerFactory method captures config identity and returns a Supplier<LDAIConfigTracker> producing a fresh tracker with a new runId on each call. Default configs also get real trackers. Default version is 1.

NoOpAIConfigTracker deleted — no longer needed.

New types

FeedbackKind — enum: POSITIVE, NEGATIVE.

TokenUsage — immutable record: total, input, output.

AIMetrics — immutable builder: success, optional tokens, durationMs, toolCalls.

JudgeResult — immutable builder: metricKey, score, sampled, success, optional judgeConfigKey, reasoning, errorMessage.

MetricSummary — snapshot of all tracked metrics plus resumption token.

TrackData — run identity fields with toLDValue().

Thread safety

All at-most-once slots use AtomicReference<T>.compareAndSet(null, value) — single atomic guard+value, no race window. Tool calls use CopyOnWriteArrayList.

Test plan

• ./gradlew :lib:sdk:server-ai:test passes
• LDAIConfigTrackerImplTest — duration (emit, clamp, at-most-once, null), durationOf (success + exception), success/error (emit, shared guard both directions), feedback (emit, at-most-once, null slot preservation), tokens (positive counts, zero skip, slot preservation), tool calls (multi-fire, null), judge result (sampled/success/metricKey/score guards, multi-fire), trackMetricsOf (success path, error path, extractor failure duration tracking, null AIMetrics guard), variationKey/graphKey in payload, concurrency (20-thread contention), constructor null rejection
• ResumptionTokensTest — encode/decode round-trips, large keys, special character escaping, null/malformed rejection, empty runId/configKey rejection