test(agent): cover the unsupported-image loop guard

The `removed == 0` branch in the recovery path is the only thing stopping
a phrase-matched 404 with no image in history from re-requesting forever:
`max_rounds` defaults to 0 (unlimited) in production, and buzz-acp's queue
retry never fires because the turn never returns.

Deleting that guard left the whole package suite green, so the branch had
no coverage. This test drives the typed error with an empty history and
asserts the turn fails with the typed error after exactly one request.

Co-authored-by: Sami <f4a42a97e594b77bdbd8ee35191c8b28a94a4cb871d96f32921558275421fb68@buzz.block.builderlab.xyz>
Signed-off-by: Sami <f4a42a97e594b77bdbd8ee35191c8b28a94a4cb871d96f32921558275421fb68@buzz.block.builderlab.xyz>

crates/buzz-agent/tests/fake_llm.rs

@@ -437,6 +437,67 @@ async fn unsupported_image_response_recovers_without_replaying_image() {
     h.shutdown().await;
 }
 
+/// The recovery path must only fire when it actually removed an image. If the
+/// provider emits the unsupported-image phrase while history holds no image
+/// (a misclassification, or a provider that returns the phrase for an
+/// unrelated reason), mutating nothing and continuing would spin the turn loop
+/// forever — `max_rounds` defaults to 0 (unlimited) in production, so nothing
+/// downstream bounds it. The turn must fail with the typed error instead.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn unsupported_image_without_image_in_history_fails_instead_of_looping() {
+    // Five rejections but MAX_ROUNDS=4: if the guard is removed the loop
+    // re-requests without ever mutating history and drains the queue.
+    let responses = (0..5)
+        .map(|_| CannedResponse {
+            status: 404,
+            body: json!({
+                "error": { "message": "No endpoints found that support image input" }
+            }),
+        })
+        .collect();
+    let (url, captures) = spawn_capturing_fake_llm_with_statuses(responses).await;
+    let mut h = Harness::spawn(&url).await;
+
+    h.send(
+        "initialize",
+        json!({"protocolVersion":2,"clientCapabilities":{}}),
+    )
+    .await;
+    let _ = h.recv().await;
+    let session_id = h
+        .send("session/new", json!({ "cwd": "/tmp", "mcpServers": [] }))
+        .await;
+    let session = h.recv_until(|v| v["id"] == json!(session_id)).await;
+    let sid = session["result"]["sessionId"].as_str().unwrap();
+
+    let prompt_id = h
+        .send(
+            "session/prompt",
+            json!({
+                "sessionId": sid,
+                "prompt": [{"type":"text","text":"no image here"}],
+            }),
+        )
+        .await;
+    let reply = h.recv_until(|v| v["id"] == json!(prompt_id)).await;
+
+    assert!(
+        reply.get("result").is_none(),
+        "an unrecoverable image rejection must not complete the turn: {reply}"
+    );
+    let message = reply["error"]["message"].as_str().unwrap_or_default();
+    assert!(
+        message.contains("image input unsupported"),
+        "the typed error must surface to the caller: {reply}"
+    );
+    assert_eq!(
+        captures.lock().await.len(),
+        1,
+        "the loop must not re-request after a rejection it could not repair"
+    );
+    h.shutdown().await;
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn rejects_concurrent_prompts() {
     // Slow first response so the second prompt arrives mid-flight.