diff --git a/riddle/src/oracle.rs b/riddle/src/oracle.rs
index 12ae27e..a69726c 100644
--- a/riddle/src/oracle.rs
+++ b/riddle/src/oracle.rs
@@ -420,7 +420,14 @@ impl HttpOracle {
         // Sent as "reasoning_effort" only when set: reasoning models accept it
         // ("low" ≈ faster first ink), but some providers reject the field on
         // non-reasoning models, so it must stay out of the default request.
-        let reasoning = std::env::var("RIDDLE_OPENAI_REASONING").ok();
+        // Set-but-EMPTY also means unset: config UIs writing env files (e.g.
+        // remagic's settings form, whose select includes a "" option) produce
+        // RIDDLE_OPENAI_REASONING= — and sending "reasoning_effort":"" is a
+        // 400 on OpenAI, silently killing every turn.
+        let reasoning = std::env::var("RIDDLE_OPENAI_REASONING")
+            .ok()
+            .map(|s| s.trim().to_string())
+            .filter(|s| !s.is_empty());
         eprintln!(
             "riddle: http oracle base={base} model={model} max_tokens={max_tokens} reasoning={}",
             reasoning.as_deref().unwrap_or("-")