Add destination takeover config policy

internal/config/load_test.go

@@ -39,6 +39,9 @@ pipelines:
 	if got, want := destination.State.Mode, StateModeSingleOwner; got != want {
 		t.Fatalf("state mode default = %q, want %q", got, want)
 	}
+	if got, want := destination.Takeover.Mode, TakeoverModeSamePipeline; got != want {
+		t.Fatalf("takeover mode default = %q, want %q", got, want)
+	}
 	if destination.Retention.Prune.Enabled {
 		t.Fatal("retention.prune.enabled default = true, want false")
 	}
@@ -231,6 +234,50 @@ pipelines:
 	}
 }
 
+func TestLoadFileAcceptsExplicitTakeoverModes(t *testing.T) {
+	cfg := loadConfig(t, `
+pipelines:
+  - id: reports
+    source:
+      backend: local
+      path: /source
+    destinations:
+      - id: same-pipeline
+        backend: local
+        path: /same-pipeline
+        takeover:
+          mode: same_pipeline
+      - id: same-source
+        backend: local
+        path: /same-source
+        takeover:
+          mode: same_source
+      - id: any-managed
+        backend: local
+        path: /any-managed
+        takeover:
+          mode: any_managed
+      - id: never
+        backend: local
+        path: /never
+        takeover:
+          mode: never
+`)
+
+	destinations := cfg.Pipelines[0].Destinations
+	wants := []string{
+		TakeoverModeSamePipeline,
+		TakeoverModeSameSource,
+		TakeoverModeAnyManaged,
+		TakeoverModeNever,
+	}
+	for index, want := range wants {
+		if got := destinations[index].Takeover.Mode; got != want {
+			t.Fatalf("destinations[%d].takeover.mode = %q, want %q", index, got, want)
+		}
+	}
+}
+
 func TestLoadFileAcceptsRetentionPruneConfig(t *testing.T) {
 	cfg := loadConfig(t, `
 pipelines:
@@ -868,6 +915,38 @@ pipelines:
 `, "on_destination_older must be replace or fail")
 }
 
+func TestLoadFileRejectsInvalidTakeoverMode(t *testing.T) {
+	assertLoadError(t, `
+pipelines:
+  - id: reports
+    source:
+      backend: local
+      path: /source
+    destinations:
+      - id: archive
+        backend: local
+        path: /archive
+        takeover:
+          mode: unmanaged
+`, "takeover.mode must be same_pipeline, same_source, any_managed, or never")
+}
+
+func TestLoadFileRejectsUnknownTakeoverFields(t *testing.T) {
+	assertLoadError(t, `
+pipelines:
+  - id: reports
+    source:
+      backend: local
+      path: /source
+    destinations:
+      - id: archive
+        backend: local
+        path: /archive
+        takeover:
+          surprise: true
+`, "field surprise not found")
+}
+
 func TestLoadFileRejectsInvalidValidationAction(t *testing.T) {
 	assertLoadError(t, `
 pipelines: