fix: prevent duplicate reasoning_details when converting messages back to API format (#344)

* fix: prevent duplicate reasoning_details when converting messages back to API format

* chore: adds changelog

* refactor: use helper function for reasoning_details deduplication

Replaces boolean flag tracking with a cleaner findFirstReasoningDetails() helper.
Priority: message-level > first tool call > first reasoning part.

* chore: improves parallel-tool-calls test coverage

Author: robert-j-y

.changeset/funny-jobs-send.md

@@ -0,0 +1,5 @@
+---
+"@openrouter/ai-sdk-provider": patch
+---
+
+Fix parallel tool calls with Claude models when thinking/reasoning is enabled. Previously, reasoning_details were duplicated across all parallel tool calls, causing Anthropic to reject continuation requests.

.gitignore

@@ -8,3 +8,5 @@ dist
 
 # Reference repositories (git submodules)
 reference/
+
+/tmp