feat(cli): the operator config surface — identity and output defaults (RFC-007 PR 1)

~/.omnigraph/config.yaml joins the resolution chains as the operator
surface: operator.actor becomes the last hop of THE actor chain (--as >
legacy cli.actor during the RFC-008 window > operator.actor > none, one
implementation for direct-engine and cluster commands alike) and
defaults.output joins the read-format cascade below every more-specific
source. Discovery honors $OMNIGRAPH_HOME (tilde-expanded, #139 finding 9);
an absent file is an empty layer; unknown keys WARN and load (a file
written for later slices must not break this CLI); malformed YAML is a
loud error. The module is CLI-only — the server never reads operator
config (invariant 11 by construction).

$OMNIGRAPH_CONFIG becomes a first-class stand-in for --config in
load_config (flag > env > ./omnigraph.yaml), one meaning in both binaries.

The test harness pins hermeticity: spawned binaries get a nonexistent
OMNIGRAPH_HOME by default so no test ever reads the developer's real
operator config. New coverage: loader unit tests, the env-precedence
matrix on load_config_in, and spawned-binary e2es for the actor chain
(operator wins with no flag/legacy key; legacy outranks it; --as wins) and
the format cascade.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/omnigraph-cli/tests/cli_data.rs

@@ -984,6 +984,52 @@ fn read_csv_format_outputs_header_and_row_values() {
     assert!(stdout.contains("Alice"));
 }
 
+/// RFC-007 PR 1: the format cascade's operator hop — `defaults.output` in
+/// ~/.omnigraph/config.yaml applies when nothing more specific is given,
+/// and `--format` still wins over it.
+#[test]
+fn read_uses_operator_default_output_format() {
+    let temp = tempdir().unwrap();
+    let graph = graph_path(temp.path());
+    init_graph(&graph);
+    load_fixture(&graph);
+    let operator_home = tempdir().unwrap();
+    fs::write(
+        operator_home.path().join("config.yaml"),
+        "defaults:\n  output: csv\n",
+    )
+    .unwrap();
+
+    let read = |extra: &[&str]| {
+        let mut command = cli();
+        command
+            .env("OMNIGRAPH_HOME", operator_home.path())
+            .arg("read")
+            .arg(&graph)
+            .arg("--query")
+            .arg(fixture("test.gq"))
+            .arg("--name")
+            .arg("get_person")
+            .arg("--params")
+            .arg(r#"{"name":"Alice"}"#);
+        for arg in extra {
+            command.arg(arg);
+        }
+        stdout_string(&output_success(&mut command))
+    };
+
+    let stdout = read(&[]);
+    assert!(
+        stdout.lines().next().unwrap().contains("p.name") && stdout.contains("Alice"),
+        "operator defaults.output: csv applies with no --format: {stdout}"
+    );
+    let stdout = read(&["--format", "jsonl"]);
+    assert!(
+        stdout.starts_with('{'),
+        "--format wins over the operator default: {stdout}"
+    );
+}
+
 #[test]
 fn read_jsonl_format_outputs_metadata_header_first() {
     let temp = tempdir().unwrap();