fix(provider): preserve reasoning_content on second interleaved pass

When the interleaved transform runs on subsequent requests (after DB
round-trip), content parts no longer contain reasoning blocks (they were
extracted on the first pass). The unconditional [field]: reasoningText
overwrites the previously correct providerOptions.reasoning_content with
empty string, causing DeepSeek 400: 'The reasoning_content in the thinking
mode must be passed back to the API.'

Fix: set [field]: reasoningText first, then spread existing providerOptions
so that preserved values from DB take priority over empty reasoningText.

Closes #24442 (co-discovered with @claudianus)

Author: knefenk

packages/opencode/src/provider/transform.ts

@@ -208,14 +208,18 @@ function normalizeMessages(
         // Include reasoning_content | reasoning_details directly on the message for all assistant messages.
         // Always set the field even when empty — some providers (e.g. DeepSeek) may return empty
         // reasoning_content which still needs to be sent back in subsequent requests.
+        // Preserve existing providerOptions[field] when content no longer has reasoning
+        // parts (e.g. after a prior transform pass already extracted them). The first
+        // pass sets the field from reasoning parts; on subsequent passes reasoningText
+        // is empty and must not overwrite the preserved value from DB.
         return {
           ...msg,
           content: filteredContent,
           providerOptions: {
             ...msg.providerOptions,
             [sdk]: {
-              ...msg.providerOptions?.[sdk],
               [field]: reasoningText,
+              ...msg.providerOptions?.[sdk],
             },
           },
         }