eval: reduce redundant work during evaluation runs

- Deduplicate concurrent Docker image builds using singleflight so
  that parallel workers needing the same image only build it once.
- Cache the structured-output judge provider across relevance checks
  instead of recreating it for every criterion. Use a mutex with
  retry-on-failure rather than sync.Once to avoid permanently caching
  transient errors (e.g. context cancellation).
- Compute getUserMessages once per eval instead of three times.

Assisted-By: docker-agent

Author: dgageot

pkg/evaluation/build.go

@@ -26,6 +26,8 @@ var (
 
 // getOrBuildImage returns a cached image ID or builds a new one.
 // Images are cached by working directory to avoid redundant builds.
+// Concurrent calls for the same working directory are deduplicated
+// using singleflight so that only one build runs at a time per key.
 func (r *Runner) getOrBuildImage(ctx context.Context, workingDir string) (string, error) {
 	r.imageCacheMu.Lock()
 	if imageID, ok := r.imageCache[workingDir]; ok {
@@ -34,16 +36,27 @@ func (r *Runner) getOrBuildImage(ctx context.Context, workingDir string) (string
 	}
 	r.imageCacheMu.Unlock()
 
-	imageID, err := r.buildEvalImage(ctx, workingDir)
+	// singleflight ensures only one build per working directory runs at a time.
+	// The cache write inside the callback guarantees the result is available
+	// before singleflight releases the key, so subsequent callers always
+	// hit the cache above.
+	v, err, _ := r.imageBuildGroup.Do(workingDir, func() (any, error) {
+		imageID, err := r.buildEvalImage(ctx, workingDir)
+		if err != nil {
+			return "", err
+		}
+
+		r.imageCacheMu.Lock()
+		r.imageCache[workingDir] = imageID
+		r.imageCacheMu.Unlock()
+
+		return imageID, nil
+	})
 	if err != nil {
 		return "", err
 	}
 
-	r.imageCacheMu.Lock()
-	r.imageCache[workingDir] = imageID
-	r.imageCacheMu.Unlock()
-
-	return imageID, nil
+	return v.(string), nil
 }
 
 func (r *Runner) buildEvalImage(ctx context.Context, workingDir string) (string, error) {

pkg/evaluation/eval.go

@@ -19,6 +19,7 @@ import (
 	"time"
 
 	"github.com/google/uuid"
+	"golang.org/x/sync/singleflight"
 
 	"github.com/docker/docker-agent/pkg/config"
 	"github.com/docker/docker-agent/pkg/config/latest"
@@ -39,6 +40,9 @@ type Runner struct {
 	// Key is the working directory (empty string for no working dir).
 	imageCache   map[string]string
 	imageCacheMu sync.Mutex
+
+	// imageBuildGroup deduplicates concurrent image builds for the same working directory.
+	imageBuildGroup singleflight.Group
 }
 
 // newRunner creates a new evaluation runner.
@@ -290,10 +294,12 @@ func (r *Runner) runSingleEval(ctx context.Context, evalSess *InputSession) (Res
 		evals = &session.EvalCriteria{}
 	}
 
+	userMessages := getUserMessages(evalSess.Session)
+
 	result := Result{
 		InputPath:         evalSess.SourcePath,
 		Title:             evalSess.Title,
-		Question:          strings.Join(getUserMessages(evalSess.Session), "\n"),
+		Question:          strings.Join(userMessages, "\n"),
 		SizeExpected:      evals.Size,
 		RelevanceExpected: float64(len(evals.Relevance)),
 	}
@@ -310,7 +316,7 @@ func (r *Runner) runSingleEval(ctx context.Context, evalSess *InputSession) (Res
 		return result, fmt.Errorf("building eval image: %w", err)
 	}
 
-	events, err := r.runDockerAgentInContainer(ctx, imageID, getUserMessages(evalSess.Session), evals.Setup)
+	events, err := r.runDockerAgentInContainer(ctx, imageID, userMessages, evals.Setup)
 	if err != nil {
 		return result, fmt.Errorf("running docker agent in container: %w", err)
 	}
@@ -323,7 +329,7 @@ func (r *Runner) runSingleEval(ctx context.Context, evalSess *InputSession) (Res
 	result.Size = getResponseSize(result.Response)
 
 	// Build session from events for database storage
-	result.Session = SessionFromEvents(events, evalSess.Title, getUserMessages(evalSess.Session))
+	result.Session = SessionFromEvents(events, evalSess.Title, userMessages)
 	result.Session.Evals = evals
 
 	if len(expectedToolCalls) > 0 || len(actualToolCalls) > 0 {

pkg/evaluation/judge.go

@@ -60,6 +60,13 @@ type Judge struct {
 	model       provider.Provider
 	runConfig   *config.RuntimeConfig
 	concurrency int
+
+	// judgeWithSchema is a provider pre-configured with structured output.
+	// Created lazily on first use and reused across all relevance checks.
+	// Protected by judgeWithSchemaMu; only cached on success so that
+	// transient errors (e.g. context cancellation) can be retried.
+	judgeWithSchema   provider.Provider
+	judgeWithSchemaMu sync.Mutex
 }
 
 // NewJudge creates a new Judge that runs relevance checks with the given concurrency.
@@ -141,16 +148,37 @@ func (j *Judge) CheckRelevance(ctx context.Context, response string, criteria []
 	return passed, failed, errs
 }
 
-// checkSingle checks a single relevance criterion against the response.
-// It returns whether the check passed, the reason provided by the judge, and any error.
-func (j *Judge) checkSingle(ctx context.Context, response, criterion string) (passed bool, reason string, err error) {
+// getOrCreateJudgeWithSchema returns a provider pre-configured with structured output.
+// The provider is created once and reused across all relevance checks.
+// Unlike sync.Once, transient failures (e.g. context cancellation) are not
+// cached, allowing subsequent calls to retry.
+func (j *Judge) getOrCreateJudgeWithSchema(ctx context.Context) (provider.Provider, error) {
+	j.judgeWithSchemaMu.Lock()
+	defer j.judgeWithSchemaMu.Unlock()
+
+	if j.judgeWithSchema != nil {
+		return j.judgeWithSchema, nil
+	}
+
 	modelCfg := j.model.BaseConfig().ModelConfig
-	judgeWithSchema, err := provider.New(
+	p, err := provider.New(
 		ctx,
 		&modelCfg,
 		j.runConfig.EnvProvider(),
 		options.WithStructuredOutput(judgeResponseSchema),
 	)
+	if err != nil {
+		return nil, err
+	}
+
+	j.judgeWithSchema = p
+	return j.judgeWithSchema, nil
+}
+
+// checkSingle checks a single relevance criterion against the response.
+// It returns whether the check passed, the reason provided by the judge, and any error.
+func (j *Judge) checkSingle(ctx context.Context, response, criterion string) (passed bool, reason string, err error) {
+	judgeWithSchema, err := j.getOrCreateJudgeWithSchema(ctx)
 	if err != nil {
 		return false, "", fmt.Errorf("creating judge provider with structured output: %w", err)
 	}