feat: language-aware PR descriptions with TL;DR for JS/TS

- Add language field to PrCommentFields interface in cf-api and cf-webapp
- For JS/TS PRs, extract first paragraph as a visible summary ("TL;DR")
  and collapse the full explanation into a <details> block
- Use correct code block language (typescript vs python) for generated
  test code in PR body
- Remove Python-specific comments from type definitions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

js/cf-api/github/create-pr-from-diffcontents.ts

@@ -38,6 +38,7 @@ export interface PrCommentFields {
   benchmark_details?: BenchmarkDetail[]
   original_async_throughput?: string
   best_async_throughput?: string
+  language?: string
 }
 
 // Dependencies interface for easier testing

js/cf-api/github/pr-changes-utils.ts

@@ -4,6 +4,10 @@ import { fileURLToPath } from "url"
 import { PrCommentFields } from "./create-pr-from-diffcontents.js"
 import { OptimizationReview } from "../OptimizationReview.js"
 
+function isJsTsLanguage(language?: string): boolean {
+  return language === "javascript" || language === "typescript"
+}
+
 export function generateOptimizationReviewTemplate(optimizationReview: string): string {
   // Return empty string if optimizationReview is empty
   if (!optimizationReview || optimizationReview === "") {
@@ -292,7 +296,39 @@ export function buildResultHeader(fields: PrCommentFields, isUnifiedReview?: boo
     .replace(/\{num_runs}/g, fields.loop_count)
 }
 
+function extractTldr(explanation: string): { summary: string; details: string } {
+  // Remove leading markdown bold header like "**Optimization Explanation:**\n"
+  const cleaned = explanation.replace(/^\*\*[^*]+\*\*:?\s*\n?/, "").trim()
+
+  // Split on double newline to get paragraphs
+  const paragraphs = cleaned.split(/\n\n+/)
+
+  if (paragraphs.length <= 1) {
+    // Single paragraph — use first two sentences as summary
+    const sentences = cleaned.match(/[^.!?\n]+[.!?]+/g)
+    if (sentences && sentences.length > 2) {
+      const summary = sentences.slice(0, 2).join("").trim()
+      const rest = cleaned.slice(summary.length).trim()
+      return { summary, details: rest }
+    }
+    return { summary: cleaned, details: "" }
+  }
+
+  // Use first paragraph as summary, rest as details
+  return { summary: paragraphs[0].trim(), details: paragraphs.slice(1).join("\n\n").trim() }
+}
+
 export function buildResultDetails(fields: PrCommentFields, isCollapsed: boolean = false): string {
+  // For JS/TS: use TL;DR format with summary up front and details collapsed
+  if (isJsTsLanguage(fields.language)) {
+    const { summary, details } = extractTldr(fields.optimization_explanation)
+    let result = `#### 📝 Summary\n\n${summary}\n`
+    if (details) {
+      result += `\n<details>\n<summary>Full explanation and details</summary>\n\n${details}\n</details>\n`
+    }
+    return result + "\n"
+  }
+
   return isCollapsed
     ? getPrDetailsTemplateCollapsed().replace(
         /\{optimization_explanation}/g,
@@ -392,8 +428,8 @@ export function buildResultTestReport(
         const trimmedGeneratedTests = generatedTests.trim()
         // Check if generatedTests already contains backticks
         if (!trimmedGeneratedTests.includes("`")) {
-          // Wrap in Python markdown block
+          const codeBlockLang = isJsTsLanguage(fields.language) ? "typescript" : "python"
-          reportTableMd += "```python\n" + trimmedGeneratedTests + "\n```"
+          reportTableMd += "```" + codeBlockLang + "\n" + trimmedGeneratedTests + "\n```"
         } else {
           reportTableMd += trimmedGeneratedTests
         }

js/cf-webapp/src/lib/types.ts

@@ -8,16 +8,17 @@ export interface DiffContents {
 }
 
 export interface PrCommentFields {
-  file_path?: string // Likely the main Python file being optimized
+  file_path?: string
   speedup_x?: string
   loop_count?: number
   speedup_pct?: string
   best_runtime?: string
   report_table?: Record<string, { failed: number; passed: number }>
-  function_name?: string // The Python function optimized
+  function_name?: string
   original_runtime?: string
   benchmark_details?: any
   optimization_explanation?: string
+  language?: string
 }
 
 export interface ExperimentMetadata {