Add strict pipeline and session config loading

internal/config/load.go

@@ -1,8 +1,68 @@
 package config
 
-import "fmt"
+import (
+	"fmt"
+	"io"
+	"os"
 
-// Load is a placeholder for strict pipeline/session config decoding.
-func Load(_ string, _ string) (*Config, error) {
-	return nil, fmt.Errorf("config load: not yet implemented")
+	"gopkg.in/yaml.v3"
+)
+
+// LoadPipeline loads pipeline configuration from a YAML file with strict field checking.
+func LoadPipeline(path string) (*PipelineConfig, error) {
+	var cfg PipelineConfig
+	if err := decodeStrictYAML(path, &cfg); err != nil {
+		return nil, fmt.Errorf("load pipeline config: %w", err)
+	}
+	return &cfg, nil
+}
+
+// LoadSession loads session configuration from a YAML file with strict field checking.
+func LoadSession(path string) (*SessionConfig, error) {
+	var cfg SessionConfig
+	if err := decodeStrictYAML(path, &cfg); err != nil {
+		return nil, fmt.Errorf("load session config: %w", err)
+	}
+	return &cfg, nil
+}
+
+// Load loads and resolves combined pipeline and session configuration.
+func Load(pipelinePath, sessionPath string) (*Config, error) {
+	pipelineCfg, err := LoadPipeline(pipelinePath)
+	if err != nil {
+		return nil, err
+	}
+
+	sessionCfg, err := LoadSession(sessionPath)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Config{
+		Pipeline:     pipelineCfg,
+		Session:      sessionCfg,
+		PipelinePath: pipelinePath,
+		SessionPath:  sessionPath,
+	}, nil
+}
+
+func decodeStrictYAML(path string, out any) error {
+	f, err := os.Open(path)
+	if err != nil {
+		return fmt.Errorf("open %q: %w", path, err)
+	}
+	defer f.Close()
+
+	dec := yaml.NewDecoder(f)
+	dec.KnownFields(true)
+	if err := dec.Decode(out); err != nil {
+		return fmt.Errorf("decode %q: %w", path, err)
+	}
+
+	var extra any
+	if err := dec.Decode(&extra); err != nil && err != io.EOF {
+		return fmt.Errorf("decode trailing content in %q: %w", path, err)
+	}
+
+	return nil
 }