diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 7c25b392..3b6418d0 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -340,6 +340,8 @@ internal documentation.
 
 ## Stage 6 — Exercise CLI Selection And Failure Reporting
 
+> Completion: complete.
+
 Goal: make derived pipelines first-class through the existing commands and
 preserve the normal load-error path for invalid inheritance.
 
diff --git a/internal/cli/configkit_commands_test.go b/internal/cli/configkit_commands_test.go
index 8f6e5115..4b33b533 100644
--- a/internal/cli/configkit_commands_test.go
+++ b/internal/cli/configkit_commands_test.go
@@ -40,6 +40,130 @@ func TestConfigKitReadOnlyCommandsLoadImportsAndOverlays(t *testing.T) {
 	}
 }
 
+func TestPipelineInheritanceCommandsSelectAndInspectDerivedPipelines(t *testing.T) {
+	t.Parallel()
+	path := writeCommandConfigContent(t, `version: 5
+pipelines:
+  " parent ":
+    input:
+      module: seriatim
+    artifacts:
+      spells:
+        extract:
+          module: dnd/spells
+    structured_output_repair_attempts: 2
+  child:
+    extends: " parent "
+    structured_output_repair_attempts: 0
+`)
+	options := commandContractOptions(t)
+
+	var stdout, stderr bytes.Buffer
+	if code := RunWithOptions([]string{"pipelines", "list", "--config", path}, &stdout, &stderr, options); code != 0 || stdout.String() != "child\nparent\n" || stderr.Len() != 0 {
+		t.Fatalf("list = %d, %q, %q", code, stdout.String(), stderr.String())
+	}
+
+	stdout.Reset()
+	stderr.Reset()
+	if code := RunWithOptions([]string{"config", "validate", "--config", path, "--pipeline", "child"}, &stdout, &stderr, options); code != 0 || !strings.Contains(stdout.String(), `is valid for pipeline "child"`) || stderr.Len() != 0 {
+		t.Fatalf("validate child = %d, %q, %q", code, stdout.String(), stderr.String())
+	}
+
+	stdout.Reset()
+	stderr.Reset()
+	if code := RunWithOptions([]string{"config", "effective", "--config", path}, &stdout, &stderr, options); code != 0 || !strings.Contains(stdout.String(), "module: seriatim") || !strings.Contains(stdout.String(), "structured_output_repair_attempts: 0") || strings.Contains(stdout.String(), "extends:") || stderr.Len() != 0 {
+		t.Fatalf("effective = %d, %q, %q", code, stdout.String(), stderr.String())
+	}
+
+	stdout.Reset()
+	stderr.Reset()
+	if code := RunWithOptions([]string{"config", "explain", "--config", path, "/pipelines/child/input/module"}, &stdout, &stderr, options); code != 0 || !strings.Contains(stdout.String(), `path: "/pipelines/child/input/module"`) || !strings.Contains(stdout.String(), "parent") || stderr.Len() != 0 {
+		t.Fatalf("explain inherited input = %d, %q, %q", code, stdout.String(), stderr.String())
+	}
+}
+
+func TestPipelineInheritanceLoadFailuresUseRuntimeDiagnostics(t *testing.T) {
+	t.Parallel()
+	for _, test := range []struct {
+		name    string
+		content string
+		args    []string
+		want    string
+	}{
+		{
+			name: "missing parent",
+			content: `version: 5
+pipelines:
+  child:
+    extends: absent
+`,
+			args: []string{"config", "validate", "--pipeline", "child"},
+			want: "inheritance.missing",
+		},
+		{
+			name: "cycle",
+			content: `version: 5
+pipelines:
+  first:
+    extends: second
+  second:
+    extends: first
+`,
+			args: []string{"config", "validate", "--pipeline", "first"},
+			want: "cycle",
+		},
+		{
+			name: "invalid directive type",
+			content: `version: 5
+pipelines:
+  child:
+    extends: 7
+`,
+			args: []string{"config", "validate", "--pipeline", "child"},
+			want: "extends",
+		},
+		{
+			name: "unselected missing parent",
+			content: `version: 5
+pipelines:
+  parent:
+    input:
+      module: seriatim
+  child:
+    extends: parent
+  unrelated:
+    extends: absent
+`,
+			args: []string{"config", "validate", "--pipeline", "child"},
+			want: "inheritance.missing",
+		},
+		{
+			name: "exact sibling mismatch",
+			content: `version: 5
+pipelines:
+  parent:
+    input:
+      module: seriatim
+  child:
+    extends: "parent "
+`,
+			args: []string{"pipelines", "list"},
+			want: "inheritance.missing",
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			path := writeCommandConfigContent(t, test.content)
+			args := append([]string{}, test.args...)
+			args = append(args, "--config", path)
+			var stdout, stderr bytes.Buffer
+			if code := RunWithOptions(args, &stdout, &stderr, commandContractOptions(t)); code != 1 || stdout.Len() != 0 || stderr.Len() == 0 || !strings.Contains(stderr.String(), test.want) {
+				t.Fatalf("code=%d stdout=%q stderr=%q", code, stdout.String(), stderr.String())
+			}
+		})
+	}
+}
+
 func TestRetiredConfigProfileFlagUsesNormalUnknownFlagBehavior(t *testing.T) {
 	t.Parallel()