Add extract worker configuration controls

internal/core/config/file_config_test.go

@@ -546,6 +546,9 @@ diagnostics:
 	if cfg.Concurrency.TotalLLM != 4 {
 		t.Fatalf("unexpected total concurrency: %d", cfg.Concurrency.TotalLLM)
 	}
+	if got := cfg.Concurrency.StageWorkers["extract"]; got != 4 {
+		t.Fatalf("default extract workers = %d, want total concurrency", got)
+	}
 	if cfg.Diagnostics.WorkDir != "/tmp/notarius-test" {
 		t.Fatalf("unexpected work dir: %q", cfg.Diagnostics.WorkDir)
 	}
@@ -554,6 +557,58 @@ diagnostics:
 	}
 }
 
+func TestApplyFileConfigStageWorkers(t *testing.T) {
+	cfg := parseAndApplyConfig(t, `
+version: 2
+concurrency:
+  total_llm: 4
+  stage_workers:
+    extract: 3
+`)
+
+	if got := cfg.Concurrency.StageWorkers["extract"]; got != 3 {
+		t.Fatalf("extract workers = %d, want 3", got)
+	}
+	if err := cfg.Validate(); err != nil {
+		t.Fatalf("Validate() error = %v, want nil", err)
+	}
+}
+
+func TestApplyFileConfigEmptyStageWorkersDefaultsExtractToTotal(t *testing.T) {
+	cfg := parseAndApplyConfig(t, `
+version: 2
+concurrency:
+  total_llm: 4
+  stage_workers: {}
+`)
+	if got := cfg.Concurrency.StageWorkers["extract"]; got != 4 {
+		t.Fatalf("extract workers = %d, want total concurrency 4", got)
+	}
+}
+
+func TestApplyFileConfigRejectsUnsupportedStageWorkerKeys(t *testing.T) {
+	for _, test := range []struct {
+		name string
+		key  string
+		want string
+	}{
+		{name: "empty", key: "' '", want: "must not be empty"},
+		{name: "unknown", key: "merge", want: "not supported"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			fileCfg, err := ParseFileConfigYAML([]byte("version: 2\nconcurrency:\n  stage_workers:\n    " + test.key + ": 1\n"))
+			if err != nil {
+				t.Fatalf("ParseFileConfigYAML() error = %v", err)
+			}
+			cfg := Default()
+			err = cfg.applyFileConfigWithLookup(fileCfg, emptyLookup)
+			if err == nil || !strings.Contains(err.Error(), test.want) {
+				t.Fatalf("ApplyFileConfig() error = %v, want %q", err, test.want)
+			}
+		})
+	}
+}
+
 func TestApplyFileConfigWorkspaceSection(t *testing.T) {
 	cfg := parseAndApplyConfig(t, `
 version: 2