Revert "fix(ui): support unified diff patch format in session changes viewer"

This reverts commit 2e9ee2cde6.

packages/ui/src/lib/diff-utils.ts

@@ -2,7 +2,6 @@ const HUNK_PATTERN = /(^|\n)@@/m
 const FILE_MARKER_PATTERN = /(^|\n)(diff --git |--- |\+\+\+)/
 const BEGIN_PATCH_PATTERN = /^\*\*\* (Begin|End) Patch/
 const UPDATE_FILE_PATTERN = /^\*\*\* Update File: (.+)$/
-const HUNK_HEADER_PATTERN = /^@@ -(\d+)(?:,(\d+))? \+(\d+)(?:,(\d+))? @@/
 
 function stripCodeFence(value: string): string {
   const trimmed = value.trim()
@@ -49,48 +48,3 @@ export function isRenderableDiffText(raw?: string | null): raw is string {
   if (!normalized) return false
   return HUNK_PATTERN.test(normalized)
 }
-
-export function parsePatchToBeforeAfter(patch: string): { before: string; after: string } {
-  if (!patch || patch.trim().length === 0) {
-    return { before: "", after: "" }
-  }
-
-  const lines = patch.replace(/\r\n/g, "\n").split("\n")
-  const beforeLines: string[] = []
-  const afterLines: string[] = []
-
-  for (const line of lines) {
-    if (line.startsWith("---") || line.startsWith("+++") || line.startsWith("diff --git")) {
-      continue
-    }
-    if (HUNK_HEADER_PATTERN.test(line)) {
-      continue
-    }
-    if (line.startsWith("-") && !line.startsWith("---")) {
-      beforeLines.push(line.slice(1))
-    } else if (line.startsWith("+") && !line.startsWith("+++")) {
-      afterLines.push(line.slice(1))
-    } else if (line.startsWith(" ")) {
-      beforeLines.push(line.slice(1))
-      afterLines.push(line.slice(1))
-    } else if (line === "") {
-      beforeLines.push("")
-      afterLines.push("")
-    } else {
-      beforeLines.push(line)
-      afterLines.push(line)
-    }
-  }
-
-  while (beforeLines.length > 0 && beforeLines[beforeLines.length - 1] === "") {
-    beforeLines.pop()
-  }
-  while (afterLines.length > 0 && afterLines[afterLines.length - 1] === "") {
-    afterLines.pop()
-  }
-
-  return {
-    before: beforeLines.join("\n"),
-    after: afterLines.join("\n"),
-  }
-}