fix: move bodyContainsImages above stableStringify comment

The helper was inserted between the stableStringify rationale comment and
the serializeBody function it describes, making the comment appear to
document bodyContainsImages. Move it above the comment so the comment
remains adjacent to serializeBody.

Co-Authored-By: OpenClaude (mimo-v2.5-pro) <openclaude@gitlawb.com>

Author: currentsuspect

src/services/api/openaiShim.ts

@@ -2112,15 +2112,6 @@ class OpenAIShimMessages {
       return false
     }
 
-    // WHY: byte-identity required for implicit prefix caching in
-    // OpenAI/Kimi/DeepSeek. stableStringify sorts object keys at every
-    // depth so spurious insertion-order differences across rebuilds of
-    // `body` (spread-merge, conditional assignments above) don't bust
-    // the provider's prefix hash.
-    //
-    // Local backends do not implement prefix caching, so the deep key-sort
-    // is pure CPU overhead per request (issue #1016). Drop to the native
-    // `JSON.stringify` fast path when the fast-path config opts out.
     const bodyContainsImages = (): boolean => {
       if (request.transport === 'responses') {
         const responsesBody = buildResponsesBody()
@@ -2140,6 +2131,15 @@ class OpenAIShimMessages {
       })
     }
 
+    // WHY: byte-identity required for implicit prefix caching in
+    // OpenAI/Kimi/DeepSeek. stableStringify sorts object keys at every
+    // depth so spurious insertion-order differences across rebuilds of
+    // `body` (spread-merge, conditional assignments above) don't bust
+    // the provider's prefix hash.
+    //
+    // Local backends do not implement prefix caching, so the deep key-sort
+    // is pure CPU overhead per request (issue #1016). Drop to the native
+    // `JSON.stringify` fast path when the fast-path config opts out.
     const serializeBody = (): string => {
       const payload =
         request.transport === 'responses' ? buildResponsesBody() : body