fix: preserve BOM in text tool round-trips (#23797)

packages/opencode/src/patch/index.ts

@@ -3,6 +3,7 @@ import * as path from "path"
 import * as fs from "fs/promises"
 import { readFileSync } from "fs"
 import { Log } from "../util"
+import * as Bom from "../util/bom"
 
 const log = Log.create({ service: "patch" })
 
@@ -305,18 +306,19 @@ export function maybeParseApplyPatch(
 interface ApplyPatchFileUpdate {
   unified_diff: string
   content: string
+  bom: boolean
 }
 
 export function deriveNewContentsFromChunks(filePath: string, chunks: UpdateFileChunk[]): ApplyPatchFileUpdate {
   // Read original file content
-  let originalContent: string
+  let originalContent: ReturnType<typeof Bom.split>
   try {
-    originalContent = readFileSync(filePath, "utf-8")
+    originalContent = Bom.split(readFileSync(filePath, "utf-8"))
   } catch (error) {
     throw new Error(`Failed to read file ${filePath}: ${error}`, { cause: error })
   }
 
-  let originalLines = originalContent.split("\n")
+  let originalLines = originalContent.text.split("\n")
 
   // Drop trailing empty element for consistent line counting
   if (originalLines.length > 0 && originalLines[originalLines.length - 1] === "") {
@@ -331,14 +333,16 @@ export function deriveNewContentsFromChunks(filePath: string, chunks: UpdateFile
     newLines.push("")
   }
 
-  const newContent = newLines.join("\n")
+  const next = Bom.split(newLines.join("\n"))
+  const newContent = next.text
 
   // Generate unified diff
-  const unifiedDiff = generateUnifiedDiff(originalContent, newContent)
+  const unifiedDiff = generateUnifiedDiff(originalContent.text, newContent)
 
   return {
     unified_diff: unifiedDiff,
     content: newContent,
+    bom: originalContent.bom || next.bom,
   }
 }
 
@@ -553,13 +557,13 @@ export async function applyHunksToFiles(hunks: Hunk[]): Promise<AffectedPaths> {
             await fs.mkdir(moveDir, { recursive: true })
           }
 
-          await fs.writeFile(hunk.move_path, fileUpdate.content, "utf-8")
+          await fs.writeFile(hunk.move_path, Bom.join(fileUpdate.content, fileUpdate.bom), "utf-8")
           await fs.unlink(hunk.path)
           modified.push(hunk.move_path)
           log.info(`Moved file: ${hunk.path} -> ${hunk.move_path}`)
         } else {
           // Regular update
-          await fs.writeFile(hunk.path, fileUpdate.content, "utf-8")
+          await fs.writeFile(hunk.path, Bom.join(fileUpdate.content, fileUpdate.bom), "utf-8")
           modified.push(hunk.path)
           log.info(`Updated file: ${hunk.path}`)
         }