feat(stream): add method to detect incomplete tool calls and handle parsing errors

src/service/provider.rs

@@ -318,6 +318,19 @@ impl LlmClient {
             }
         }
 
+        // The connection closed without an explicit `[DONE]` event. Some
+        // providers legitimately omit it, so EOF alone isn't an error —
+        // but if it leaves a tool call's arguments as unparsable JSON, the
+        // response was truncated mid-generation, not finished. Report that
+        // honestly instead of silently double-stringifying the fragment
+        // into a tool call that will misbehave (e.g. a `write` call with a
+        // half-written file body).
+        if let Some((name, err)) = turn.incomplete_tool_call() {
+            anyhow::bail!(
+                "stream ended before tool call '{name}' arguments were complete: {err}"
+            );
+        }
+
         turn.is_complete = true;
         Ok((turn.build_assistant_message(), usage))
     }