Add extract worker configuration controls

internal/core/config/file_config.go

@@ -43,7 +43,8 @@ type FileArtifactLaneProfile struct {
 }
 
 type FileConcurrencyConfig struct {
-	TotalLLM *int `yaml:"total_llm,omitempty"`
+	TotalLLM     *int           `yaml:"total_llm,omitempty"`
+	StageWorkers map[string]int `yaml:"stage_workers,omitempty"`
 }
 
 type FileDiagnosticsConfig struct {
@@ -316,6 +317,15 @@ func (c *Config) applyFileConfigWithLookup(fileCfg FileConfig, lookup func(strin
 	if fileCfg.Concurrency != nil && fileCfg.Concurrency.TotalLLM != nil {
 		c.Concurrency.TotalLLM = *fileCfg.Concurrency.TotalLLM
 	}
+	if fileCfg.Concurrency != nil && fileCfg.Concurrency.StageWorkers != nil {
+		workers, configured, err := normalizeStageWorkers(fileCfg.Concurrency.StageWorkers)
+		if err != nil {
+			return err
+		}
+		c.Concurrency.StageWorkers = workers
+		c.Concurrency.extractWorkersConfigured = configured
+	}
+	c.Concurrency.recomputeStageWorkerDefaults()
 	if fileCfg.Diagnostics != nil {
 		if fileCfg.Diagnostics.WorkDir != nil {
 			c.Diagnostics.WorkDir = strings.TrimSpace(*fileCfg.Diagnostics.WorkDir)
@@ -350,6 +360,26 @@ func (c *Config) applyFileConfigWithLookup(fileCfg FileConfig, lookup func(strin
 	return nil
 }
 
+func normalizeStageWorkers(values map[string]int) (map[string]int, bool, error) {
+	workers := make(map[string]int, len(values))
+	configured := false
+	for rawKey, value := range values {
+		key := strings.TrimSpace(rawKey)
+		if key == "" {
+			return nil, false, fmt.Errorf("concurrency.stage_workers key must not be empty")
+		}
+		if key != "extract" {
+			return nil, false, fmt.Errorf("concurrency.stage_workers key %q is not supported", rawKey)
+		}
+		if _, exists := workers[key]; exists {
+			return nil, false, fmt.Errorf("concurrency.stage_workers key %q is duplicated after trimming", key)
+		}
+		workers[key] = value
+		configured = true
+	}
+	return workers, configured, nil
+}
+
 func normalizedMapKeys[T any](values map[string]T, keyName string) ([]string, map[string]string, error) {
 	keys := make([]string, 0, len(values))
 	rawByNormalized := make(map[string]string, len(values))