Reject incomplete AI completions before showing generated answers

crates/searchi-ai/src/lib.rs

@@ -165,6 +165,15 @@ impl AiClient {
             .into_iter()
             .next()
             .ok_or(AiError::InvalidResponse("AI endpoint returned no choices"))?;
+        if choice
+            .finish_reason
+            .as_deref()
+            .is_some_and(|reason| reason != "stop")
+        {
+            return Err(AiError::InvalidResponse(
+                "AI endpoint did not finish a complete answer",
+            ));
+        }
         let content = choice.message.content.ok_or(AiError::InvalidResponse(
             "AI endpoint returned no textual content",
         ))?;
@@ -351,6 +360,9 @@ struct Completion {
 #[derive(Deserialize)]
 struct Choice {
     message: Message,
+    // Some compatible local servers omit this. When present, incomplete,
+    // filtered or tool-directed completions must not appear as finished drafts.
+    finish_reason: Option<String>,
 }
 #[derive(Deserialize)]
 struct Message {

crates/searchi-ai/src/tests.rs

@@ -20,6 +20,39 @@ fn completion(answer: &str, citations: Vec<&str>) -> Vec<u8> {
     serde_json::to_vec(&serde_json::json!({"choices":[{"message":{"content":serde_json::json!({"answer":answer,"citations":citations}).to_string()}}]})).unwrap()
 }
 type Wire = Arc<Mutex<Option<(String, Vec<u8>)>>>;
+
+#[test]
+fn incomplete_or_filtered_completions_are_not_accepted_as_finished_answers() {
+    for reason in ["length", "content_filter", "tool_calls", "unexpected"] {
+        let mut body: serde_json::Value = serde_json::from_slice(&completion(
+            "Sixty days written notice. [selected]",
+            vec!["selected"],
+        ))
+        .unwrap();
+        body["choices"][0]["finish_reason"] = serde_json::json!(reason);
+        let (base, _, worker) = server(200, serde_json::to_vec(&body).unwrap(), Duration::ZERO);
+        let result = AiClient::new(config(base)).unwrap().generate(&request());
+        worker.join().unwrap();
+        assert_eq!(
+            result.unwrap_err(),
+            AiError::InvalidResponse("AI endpoint did not finish a complete answer")
+        );
+    }
+}
+
+#[test]
+fn explicit_stop_completion_is_accepted() {
+    let mut body: serde_json::Value = serde_json::from_slice(&completion(
+        "Sixty days written notice. [selected]",
+        vec!["selected"],
+    ))
+    .unwrap();
+    body["choices"][0]["finish_reason"] = serde_json::json!("stop");
+    let (base, _, worker) = server(200, serde_json::to_vec(&body).unwrap(), Duration::ZERO);
+    let result = AiClient::new(config(base)).unwrap().generate(&request());
+    worker.join().unwrap();
+    assert!(result.is_ok());
+}
 fn server(status: u16, body: Vec<u8>, delay: Duration) -> (String, Wire, thread::JoinHandle<()>) {
     server_with_length(status, body, delay, true)
 }

docs/AI-ANSWERS.md

@@ -49,6 +49,14 @@ model is instructed to return JSON containing `answer` and `citations` inside
 chosen model must follow that instruction. Unknown source citations and invalid
 responses produce an error; search remains available.
 
+When an endpoint provides `choices[0].finish_reason`, it must be `stop`.
+Truncated (`length`), filtered, tool-directed and unknown completion reasons
+are rejected even if the returned text happens to parse as valid cited JSON.
+Compatible local servers may omit this field. Nine local HTTP adapter tests
+passed on 2026-10-13, including explicit completion reasons, citation validation,
+credential handling, response limits and timeouts; strict Clippy passed.
+This does not validate any hosted provider or generated answer accuracy.
+
 Requests use timeouts and size limits. Redirects and ambient proxies are
 disabled to keep the configured destination explicit. Endpoint URLs must use
 HTTP or HTTPS and must not contain embedded credentials, query strings or