Add BrokerPort: loopd asks brokerd for every tool call

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/loopd/tests/config.rs

@@ -224,3 +224,49 @@ fn unknown_keys_are_errors_in_the_m2b_tables_too() {
         "a partial table keeps the other defaults"
     );
 }
+
+#[test]
+fn the_broker_table_is_optional_and_its_socket_has_no_default() {
+    let c = Config::load(&fixture("minimal.toml")).unwrap();
+    assert_eq!(
+        c.broker.socket, None,
+        "no socket means no broker, never a guessed path"
+    );
+    assert_eq!(c.broker.timeout_ms, 120_000);
+}
+
+#[test]
+fn the_broker_table_can_be_set_and_rejects_unknown_keys() {
+    let base = std::fs::read_to_string(fixture("m2b.toml")).unwrap();
+    let text = format!(
+        "{base}\n[broker]\nsocket = \"/run/boxmaker/loop-broker/broker.sock\"\ntimeout_ms = 5000\n"
+    );
+    let c = Config::parse(&text).unwrap();
+    assert_eq!(
+        c.broker.socket,
+        Some(PathBuf::from("/run/boxmaker/loop-broker/broker.sock"))
+    );
+    assert_eq!(c.broker.timeout_ms, 5000);
+
+    let only_timeout = format!("{base}\n[broker]\ntimeout_ms = 5000\n");
+    let c = Config::parse(&only_timeout).unwrap();
+    assert_eq!((c.broker.socket, c.broker.timeout_ms), (None, 5000));
+
+    let only_socket = format!("{base}\n[broker]\nsocket = \"/b.sock\"\n");
+    let c = Config::parse(&only_socket).unwrap();
+    assert_eq!(
+        c.broker.timeout_ms, 120_000,
+        "a partial table keeps the default"
+    );
+
+    for bad in [
+        "zz_unknown = 1",
+        "timeout = 5000",
+        "timeout_ms = -1",
+        "timeout_ms = \"5s\"",
+        "socket = 7",
+    ] {
+        let text = format!("{base}\n[broker]\n{bad}\n");
+        assert!(Config::parse(&text).is_err(), "[broker] accepted `{bad}`");
+    }
+}