1 files changed, 48 insertions, 4 deletions

diff --git a/libpanto/src/provider_openai_chat.zig b/libpanto/src/provider_openai_chat.zig
index f653ff6..a05c7ba 100644
--- a/libpanto/src/provider_openai_chat.zig
+++ b/libpanto/src/provider_openai_chat.zig
@@ -674,23 +674,23 @@ fn handleEvent(
         try out.push(.{ .message_start = .assistant });
     }
 
-    if (d.reasoning_content) |rc| {
+    if (d.reasoning_content) |rc| if (rc.len > 0) {
         if (!state.started) {
             state.started = true;
             try out.push(.{ .message_start = .assistant });
         }
         try state.openBlock(.thinking, out);
         try state.appendDelta(out, rc);
-    }
+    };
 
-    if (d.content) |c| {
+    if (d.content) |c| if (c.len > 0) {
         if (!state.started) {
             state.started = true;
             try out.push(.{ .message_start = .assistant });
         }
         try state.openBlock(.text, out);
         try state.appendDelta(out, c);
-    }
+    };
 
     if (d.tool_calls.len > 0) {
         if (!state.started) {
@@ -909,6 +909,50 @@ test "openai_chat: omitted stream usage yields null on message_complete" {
     try testing.expectEqualStrings("msg_complete[usage:null]", found.?);
 }
 
+test "openai_chat: empty content alongside reasoning does not split thinking block" {
+    const allocator = testing.allocator;
+
+    var conv = conversation.Conversation.init(allocator);
+    defer conv.deinit();
+    try addUserText(&conv, "think");
+
+    var rec = EventRecorder{ .allocator = allocator };
+    defer rec.deinit();
+
+    const events = [_][]const u8{
+        \\{"choices":[{"delta":{"role":"assistant"}}]}
+        ,
+        \\{"choices":[{"delta":{"reasoning_content":"rea","content":""}}]}
+        ,
+        \\{"choices":[{"delta":{"reasoning_content":"son","content":""}}]}
+        ,
+        \\{"choices":[{"delta":{"reasoning_content":"ing","content":""}}]}
+        ,
+        \\{"choices":[{"delta":{},"finish_reason":"stop"}]}
+        ,
+        "[DONE]",
+    };
+    try runStreamedTurn(allocator, &conv, &rec, &events);
+
+    const expected = [_][]const u8{
+        "msg_start",
+        "block_start[0]:Thinking",
+        "delta[0]:rea",
+        "delta[0]:son",
+        "delta[0]:ing",
+        "block_complete[0]",
+        "msg_complete[usage:null]",
+    };
+    try testing.expectEqual(expected.len, rec.events.items.len);
+    for (expected, rec.events.items) |want, got| {
+        try testing.expectEqualStrings(want, got);
+    }
+
+    const asst = conv.messages.items[1];
+    try testing.expectEqual(@as(usize, 1), asst.content.items.len);
+    try testing.expectEqualStrings("reasoning", asst.content.items[0].Thinking.text.items);
+}
+
 test "fragmented tool_call id and name are reassembled" {
     // Lenient OpenAI-compatible providers occasionally split `id` and
     // `function.name` across multiple deltas instead of sending them whole