Add reconciliation state foundation

internal/config/config.go

@@ -38,24 +38,25 @@ type Pipeline struct {
 }
 
 type Destination struct {
-	ID        string         `yaml:"id"`
-	Backend   string         `yaml:"backend"`
-	Host      string         `yaml:"host"`
-	User      string         `yaml:"user"`
-	Port      int            `yaml:"port"`
-	Path      string         `yaml:"path"`
-	Endpoint  string         `yaml:"endpoint"`
-	Bucket    string         `yaml:"bucket"`
-	Prefix    string         `yaml:"prefix"`
-	Region    string         `yaml:"region"`
-	ForcePath *bool          `yaml:"force_path_style"`
-	Creds     Credentials    `yaml:"credentials"`
-	SSH       SSH            `yaml:",inline"`
-	Publish   *PublishPolicy `yaml:"publish"`
-	Transform Transform      `yaml:"transform"`
-	PathMap   PathMapping    `yaml:"path_mapping"`
-	Links     *Links         `yaml:"links"`
-	Transfer  TransferPolicy `yaml:"transfer"`
+	ID             string               `yaml:"id"`
+	Backend        string               `yaml:"backend"`
+	Host           string               `yaml:"host"`
+	User           string               `yaml:"user"`
+	Port           int                  `yaml:"port"`
+	Path           string               `yaml:"path"`
+	Endpoint       string               `yaml:"endpoint"`
+	Bucket         string               `yaml:"bucket"`
+	Prefix         string               `yaml:"prefix"`
+	Region         string               `yaml:"region"`
+	ForcePath      *bool                `yaml:"force_path_style"`
+	Creds          Credentials          `yaml:"credentials"`
+	SSH            SSH                  `yaml:",inline"`
+	Publish        *PublishPolicy       `yaml:"publish"`
+	Transform      Transform            `yaml:"transform"`
+	PathMap        PathMapping          `yaml:"path_mapping"`
+	Links          *Links               `yaml:"links"`
+	Reconciliation ReconciliationPolicy `yaml:"reconciliation"`
+	Transfer       TransferPolicy       `yaml:"transfer"`
 }
 
 type Backend struct {
@@ -118,6 +119,10 @@ type Links struct {
 	Primary string `yaml:"primary"`
 }
 
+type ReconciliationPolicy struct {
+	Mode string `yaml:"mode"`
+}
+
 type TransferPolicy struct {
 	OnDestinationSame  string `yaml:"on_destination_same"`
 	OnDestinationOlder string `yaml:"on_destination_older"`

internal/config/defaults.go

@@ -42,6 +42,11 @@ const (
 	LinkPrimarySource = "source"
 )
 
+const (
+	ReconciliationModeReplace = "replace"
+	ReconciliationModeMerge   = "merge"
+)
+
 const DefaultS3Region = "us-east-1"
 
 const (
@@ -79,6 +84,9 @@ func ApplyDefaults(cfg *Config) {
 			if destination.Links != nil && destination.Links.Primary == "" {
 				destination.Links.Primary = LinkPrimaryAuto
 			}
+			if destination.Reconciliation.Mode == "" {
+				destination.Reconciliation.Mode = ReconciliationModeReplace
+			}
 			if destination.Transfer.OnDestinationSame == "" {
 				destination.Transfer.OnDestinationSame = TransferActionSkip
 			}

internal/config/load_test.go

@@ -33,6 +33,9 @@ pipelines:
 	if got, want := destination.Transfer.OnDestinationOlder, TransferActionReplace; got != want {
 		t.Fatalf("transfer default = %q, want %q", got, want)
 	}
+	if got, want := destination.Reconciliation.Mode, ReconciliationModeReplace; got != want {
+		t.Fatalf("reconciliation mode default = %q, want %q", got, want)
+	}
 	if cfg.Secrets.Directory != "" {
 		t.Fatalf("secrets.directory = %q, want empty", cfg.Secrets.Directory)
 	}
@@ -164,6 +167,35 @@ pipelines:
 	}
 }
 
+func TestLoadFileAcceptsExplicitReconciliationModes(t *testing.T) {
+	cfg := loadConfig(t, `
+pipelines:
+  - id: reports
+    source:
+      backend: local
+      path: /source
+    destinations:
+      - id: archive
+        backend: local
+        path: /archive
+        reconciliation:
+          mode: replace
+      - id: web
+        backend: local
+        path: /web
+        reconciliation:
+          mode: merge
+`)
+
+	destinations := cfg.Pipelines[0].Destinations
+	if got, want := destinations[0].Reconciliation.Mode, ReconciliationModeReplace; got != want {
+		t.Fatalf("archive reconciliation mode = %q, want %q", got, want)
+	}
+	if got, want := destinations[1].Reconciliation.Mode, ReconciliationModeMerge; got != want {
+		t.Fatalf("web reconciliation mode = %q, want %q", got, want)
+	}
+}
+
 func TestLoadFileAcceptsFixedPathMapping(t *testing.T) {
 	cfg := loadConfig(t, `
 pipelines:

internal/config/validate.go

@@ -72,6 +72,7 @@ func Validate(cfg Config) error {
 			errs = validatePublishTransformPolicy(errs, destinationContext, destination.Publish, destination.Transform)
 			errs = validatePathMapping(errs, destinationContext+".path_mapping", destination.PathMap)
 			errs = validateLinks(errs, destinationContext+".links", destination.Links)
+			errs = validateReconciliationPolicy(errs, destinationContext+".reconciliation", destination.Reconciliation)
 			errs = validateTransferPolicy(errs, destinationContext+".transfer", destination.Transfer)
 		}
 	}
@@ -314,6 +315,13 @@ func validateLinks(errs ValidationErrors, context string, links *Links) Validati
 	return errs
 }
 
+func validateReconciliationPolicy(errs ValidationErrors, context string, policy ReconciliationPolicy) ValidationErrors {
+	if policy.Mode != ReconciliationModeReplace && policy.Mode != ReconciliationModeMerge {
+		errs = append(errs, context+".mode must be "+ReconciliationModeReplace+" or "+ReconciliationModeMerge)
+	}
+	return errs
+}
+
 func validateTransferPolicy(errs ValidationErrors, context string, policy TransferPolicy) ValidationErrors {
 	if policy.OnDestinationSame != TransferActionSkip && policy.OnDestinationSame != TransferActionFail {
 		errs = append(errs, context+".on_destination_same must be skip or fail")

internal/config/validate_test.go

@@ -107,6 +107,40 @@ func TestValidatePathMapping(t *testing.T) {
 	}
 }
 
+func TestValidateReconciliationPolicy(t *testing.T) {
+	tests := []struct {
+		name    string
+		mode    string
+		wantErr bool
+	}{
+		{name: "replace", mode: ReconciliationModeReplace},
+		{name: "merge", mode: ReconciliationModeMerge},
+		{name: "invalid", mode: "append", wantErr: true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := Config{Pipelines: []Pipeline{{
+				ID:     "reports",
+				Source: Backend{Backend: BackendLocal, Path: "/source"},
+				Destinations: []Destination{{
+					ID:             "archive",
+					Backend:        BackendLocal,
+					Path:           "/destination",
+					Reconciliation: ReconciliationPolicy{Mode: tt.mode},
+				}},
+			}}}
+			ApplyDefaults(&cfg)
+			err := Validate(cfg)
+			if tt.wantErr && err == nil {
+				t.Fatal("Validate() error = nil, want error")
+			}
+			if !tt.wantErr && err != nil {
+				t.Fatalf("Validate() error = %v", err)
+			}
+		})
+	}
+}
+
 func TestValidateLinks(t *testing.T) {
 	tests := []struct {
 		name    string