swarm-controller: refuse an inference model name that starts with "-"

`check_model` accepted a value like `--dangerously-skip-permissions`,
and the stored model ends up in the agent's `claude` argv. A PUT whose
`model`, or any `subagent_models` entry (same validator), starts with
`-` is now a 400 with the same problem+json shape as the other model
checks. A dash inside a name (`claude-opus-4-8`) is still accepted.

Raised by argus on #5084.

Refs #5034

docs/swarm/inference.md

@@ -82,11 +82,11 @@ which swarm-controller alone writes:
 
 Every field is optional, and `{}` reads the same as no key.
 
-| method   | path                            | body                                                                                                                                 |
-| -------- | ------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------ |
-| `GET`    | `/api/agents/<agent>/inference` | —; answers `{"configured": <the stored value, {} when none>, "effective": <what the agent reported, or null>}`                       |
-| `PUT`    | `/api/agents/<agent>/inference` | the whole value, replacing the stored one; the controller refuses unknown fields, an unknown effort, or a model name with whitespace |
-| `DELETE` | `/api/agents/<agent>/inference` | —; answers 204                                                                                                                       |
+| method   | path                            | body                                                                                                                                                  |
+| -------- | ------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `GET`    | `/api/agents/<agent>/inference` | —; answers `{"configured": <the stored value, {} when none>, "effective": <what the agent reported, or null>}`                                        |
+| `PUT`    | `/api/agents/<agent>/inference` | the whole value, replacing the stored one; the controller refuses unknown fields, an unknown effort, or a model name with whitespace or a leading `-` |
+| `DELETE` | `/api/agents/<agent>/inference` | —; answers 204                                                                                                                                        |
 
 An agent's own queue credential grants it
 `$JS.API.DIRECT.GET.KV_agent-inference.$KV.agent-inference.<agent>`, the

swarm-controller/src/inference.rs

@@ -59,7 +59,8 @@ impl From<AgentInference> for InferenceSettings {
     }
 }
 
-/// A model name as the agent passes it to claude: one non-empty word.
+/// A model name as the agent passes it to claude: one non-empty word that
+/// cannot be read as a command-line flag.
 fn check_model(name: &str, what: &str) -> Result<(), String> {
     if name.is_empty() {
         return Err(format!("the {what} is empty"));
@@ -67,6 +68,9 @@ fn check_model(name: &str, what: &str) -> Result<(), String> {
     if name.chars().any(|c| c.is_whitespace() || c.is_control()) {
         return Err(format!("the {what} {name:?} contains whitespace"));
     }
+    if name.starts_with('-') {
+        return Err(format!("the {what} {name:?} starts with \"-\""));
+    }
     Ok(())
 }
 
@@ -259,7 +263,8 @@ pub(crate) async fn get_agent_inference(
         (status = 200, description = "the settings as stored; they replace the previous \
             ones whole", body = InferenceSettings),
         (status = 400, description = "not an identifier, not declared on any hive, or a \
-            model name is empty, has whitespace, or is listed twice (problem+json)",
+            model name is empty, has whitespace, starts with `-`, or is listed twice \
+            (problem+json)",
             body = String),
         (status = 422, description = "an unknown field, or an effort that is not one of \
             the five levels"),
@@ -465,8 +470,18 @@ mod tests {
             r#"{"subagent_models":[]}"#,
             r#"{"subagent_models":["haiku",""]}"#,
             r#"{"subagent_models":["haiku","haiku"]}"#,
+            r#"{"model":"--dangerously-skip-permissions"}"#,
+            r#"{"model":"-x"}"#,
+            r#"{"subagent_models":["haiku","--print"]}"#,
         ] {
             assert!(settings(json).unwrap().into_stored().is_err(), "{json}");
         }
     }
+
+    /// Control for the leading-dash refusal: full model ids have dashes inside.
+    #[test]
+    fn a_dash_inside_a_model_name_is_accepted() {
+        let json = r#"{"model":"claude-opus-4-8","subagent_models":["claude-haiku-4-5"]}"#;
+        assert!(settings(json).unwrap().into_stored().is_ok());
+    }
 }

swarm-controller/src/main.rs

@@ -5544,17 +5544,16 @@ mod tests {
                 "DELETE {name}"
             );
         }
-        assert_eq!(
-            status(
-                put_agent_inference(
-                    State(state),
-                    Path("iris".to_owned()),
-                    body(r#"{"model":"opus 4"}"#)
-                )
-                .await
-            ),
-            Some(StatusCode::BAD_REQUEST)
-        );
+        for bad in [r#"{"model":"opus 4"}"#, r#"{"model":"--print"}"#] {
+            assert_eq!(
+                status(
+                    put_agent_inference(State(state.clone()), Path("iris".to_owned()), body(bad))
+                        .await
+                ),
+                Some(StatusCode::BAD_REQUEST),
+                "{bad}"
+            );
+        }
     }
 
     #[tokio::test]