fix: handle unclosed <think> tags from truncated model output

When the small model hits its token limit mid-generation, `<think>` tags
may not have a closing `</think>`. The previous regex required a closing
tag, which would leak the entire reasoning block into the enhanced prompt.

Now `stripThinkTags()` matches both closed and unclosed think blocks.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: anandgupta42

packages/opencode/src/altimate/enhance-prompt.ts

@@ -54,7 +54,9 @@ User: "migrate this from snowflake to bigquery"
 Enhanced: "Migrate the SQL from Snowflake dialect to BigQuery dialect. Convert Snowflake-specific functions (e.g. DATEADD, IFF, QUALIFY) to BigQuery equivalents. Preserve the query logic and verify the translated query is syntactically valid."`
 
 export function stripThinkTags(text: string) {
-  return text.replace(/<think>[\s\S]*?<\/think>\s*/g, "")
+  // Match closed <think>...</think> blocks, and also unclosed <think>... to end of string
+  // (unclosed tags happen when the model hits token limit mid-generation)
+  return text.replace(/<think>[\s\S]*?(?:<\/think>\s*|$)/g, "")
 }
 
 export function clean(text: string) {

packages/opencode/test/altimate/enhance-prompt.test.ts

@@ -108,6 +108,14 @@ describe("enhance-prompt stripThinkTags()", () => {
   test("handles nested angle brackets inside think tags", () => {
     expect(stripThinkTags("<think>check if x < 5 and y > 3</think>result")).toBe("result")
   })
+
+  test("strips unclosed think tag (model hit token limit)", () => {
+    expect(stripThinkTags("<think>reasoning that got cut off")).toBe("")
+  })
+
+  test("strips unclosed think tag with content before it", () => {
+    expect(stripThinkTags("good content <think>trailing reasoning")).toBe("good content ")
+  })
 })
 
 describe("enhance-prompt combined pipeline", () => {