feat(claw): serve the vision flag on model listings

The models route's cards serialize as rhema-provider's ModelCard
spells them, so supports_vision rides exactly when the adapter knows
it and is absent when it does not — unknown stays absent, never
false. The route's doc now pins that contract, and a listing builder
on Backend lets the surface tests mount one offline.

crates/rhema-claw/src/backends.rs

@@ -115,6 +115,18 @@ impl Backend {
             list_models: None,
         }
     }
+
+    /// Attaches a live listing. [`construct`] builds the real ones off
+    /// the provider; this shape exists so the surface's model routes
+    /// can be exercised offline — a test mounts a listing over a
+    /// scripted card set.
+    pub fn with_listing(
+        mut self,
+        list_models: impl Fn() -> ModelListing + Send + Sync + 'static,
+    ) -> Self {
+        self.list_models = Some(Arc::new(list_models));
+        self
+    }
 }
 
 /// The currently active backend instance: id plus the model turns run on.

crates/rhema-claw/src/http.rs

@@ -1864,8 +1864,12 @@ async fn providers_active(
 }
 
 /// `GET /v1/providers/{id}/models`: the instance's live listing,
-/// straight from the provider. An id without a listing (unknown, or the
-/// mock) is a 404.
+/// straight from the provider, the cards serialized as rhema-provider's
+/// `ModelCard` spells them. `supports_vision` rides when the adapter
+/// knows — `true` or `false` — and is absent when it does not: unknown
+/// stays absent, never `false`, and a client reads the key's absence as
+/// no verdict at all. An id without a listing (unknown, or the mock) is
+/// a 404.
 async fn providers_models(
     State(state): State<ClawState>,
     Path(id): Path<String>,

crates/rhema-claw/tests/http.rs

@@ -1630,6 +1630,67 @@ async fn providers_are_listed_switched_and_persisted() {
     assert_eq!(daemon.backends().active().1, "mock-large");
 }
 
+/// The models route: the cards serialize as rhema-provider's
+/// `ModelCard`, so a model the adapter knows is vision-capable rides
+/// with `supports_vision: true` and an unknown one omits the key
+/// entirely — unknown stays absent, never `false`.
+#[tokio::test]
+async fn model_listings_carry_the_vision_flag_only_when_known() {
+    let card = |id: &str, vision: Option<bool>| rhema_provider::ModelCard {
+        id: id.to_owned(),
+        display_name: id.to_owned(),
+        description: String::new(),
+        input_token_limit: None,
+        output_token_limit: None,
+        supports_vision: vision,
+        generation_methods: vec!["generateContent".to_owned()],
+        pricing: None,
+    };
+    let cards = vec![
+        card("claude-sonnet-4-5", Some(true)),
+        card("some-foreign-model", None),
+    ];
+    let backend =
+        rhema_claw::Backend::headless("anthropic", Arc::new(MockProvider::new([reply("on it")])))
+            .with_listing(move || {
+                let cards = cards.clone();
+                Box::pin(async move { Ok(cards) })
+            });
+    let dir = tempfile::tempdir().expect("tempdir");
+    let daemon = Daemon::build(
+        &config(&dir, None),
+        Arc::new(
+            rhema_claw::BackendRegistry::new(vec![backend], None)
+                .expect("a single backend always constructs"),
+        ),
+        rhema_rsd::DispatcherConfig::default(),
+    )
+    .expect("the daemon assembles");
+    let base = serve(&daemon).await;
+
+    let listed: Value = reqwest::Client::new()
+        .get(format!("{base}/v1/providers/anthropic/models"))
+        .send()
+        .await
+        .expect("the listing reads")
+        .json()
+        .await
+        .expect("the listing parses");
+    let entries = listed["models"].as_array().expect("the models array");
+    assert_eq!(entries.len(), 2, "{listed}");
+    assert_eq!(entries[0]["id"], "claude-sonnet-4-5");
+    assert_eq!(
+        entries[0]["supports_vision"], true,
+        "a known-vision model says so: {listed}"
+    );
+    assert_eq!(entries[1]["id"], "some-foreign-model");
+    assert!(
+        entries[1].get("supports_vision").is_none(),
+        "unknown stays absent, not false: {:?}",
+        entries[1]
+    );
+}
+
 /// The credentials surface: a runtime login adds a backend, the list
 /// names where its credential came from, a re-add replaces it in place,
 /// and a removal drops it — refusing to remove the last backend, and