diff --git a/src/renderer/src/components/editor/rich-markdown-review-annotations.ts b/src/renderer/src/components/editor/rich-markdown-review-annotations.ts
index 619d128bb65..90bd170a5c1 100644
--- a/src/renderer/src/components/editor/rich-markdown-review-annotations.ts
+++ b/src/renderer/src/components/editor/rich-markdown-review-annotations.ts
@@ -139,7 +139,7 @@ export function getRichMarkdownAnnotationHighlightRangesForComment(
   comment: DiffComment,
   markdownSourceLineOffset: number,
   // Why optional: callers looping over comments pass one shared build.
-  prebuiltBlocks?: RichMarkdownCommentBlock[]
+  prebuiltBlocks?: readonly RichMarkdownCommentBlock[]
 ): RichMarkdownAnnotationHighlightRange[] {
   const blocks = prebuiltBlocks ?? buildRichMarkdownCommentBlocks(editor)
   const selectedText = comment.selectedText?.trim()
@@ -192,13 +192,15 @@ export function getRichMarkdownCommentAnchorTop(
   block: RichMarkdownCommentBlock,
   containerRect: DOMRect,
   containerScrollTop: number,
-  markdownSourceLineOffset: number
+  markdownSourceLineOffset: number,
+  prebuiltBlocks?: readonly RichMarkdownCommentBlock[]
 ): number | null {
   try {
     const ranges = getRichMarkdownAnnotationHighlightRangesForComment(
       editor,
       comment,
-      markdownSourceLineOffset
+      markdownSourceLineOffset,
+      prebuiltBlocks
     )
     // Why: range notes should sort by the start of the selected text. Anchoring
     // to the end puts overlapping ranges with the same final line in creation
diff --git a/src/renderer/src/components/editor/rich-markdown-review-note-positioning.ts b/src/renderer/src/components/editor/rich-markdown-review-note-positioning.ts
index c54996d0ffa..4fdc12a51b9 100644
--- a/src/renderer/src/components/editor/rich-markdown-review-note-positioning.ts
+++ b/src/renderer/src/components/editor/rich-markdown-review-note-positioning.ts
@@ -1,9 +1,7 @@
 import type { Editor } from '@tiptap/react'
 import type { DiffComment } from '../../../../shared/diff-comment-types'
-import {
-  buildRichMarkdownCommentBlocks,
-  getRichMarkdownCommentAnchorTop
-} from './rich-markdown-review-annotations'
+import { getRichMarkdownCommentAnchorTop } from './rich-markdown-review-annotations'
+import { getRichMarkdownReviewRailBlocks } from './rich-markdown-review-rail-blocks'
 import {
   stackRichMarkdownReviewNotePositions,
   type RichMarkdownReviewNotePosition
@@ -23,7 +21,7 @@ export function measureRichMarkdownReviewNotePositions({
   markdownSourceLineOffset
 }: MeasureRichMarkdownReviewNotePositionsOptions): RichMarkdownReviewNotePosition[] {
   const containerRect = container.getBoundingClientRect()
-  const blocks = buildRichMarkdownCommentBlocks(editor)
+  const blocks = getRichMarkdownReviewRailBlocks(editor)
   const nextPositions = markdownComments
     .map((comment): RichMarkdownReviewNotePosition | null => {
       const bodyLineNumber = Math.max(1, comment.lineNumber - markdownSourceLineOffset)
@@ -39,7 +37,8 @@ export function measureRichMarkdownReviewNotePositions({
         block,
         containerRect,
         container.scrollTop,
-        markdownSourceLineOffset
+        markdownSourceLineOffset,
+        blocks
       )
       return top === null ? null : { comment, top }
     })
diff --git a/src/renderer/src/components/editor/rich-markdown-review-rail-benchmark.test.ts b/src/renderer/src/components/editor/rich-markdown-review-rail-benchmark.test.ts
new file mode 100644
index 00000000000..7090769f71f
--- /dev/null
+++ b/src/renderer/src/components/editor/rich-markdown-review-rail-benchmark.test.ts
@@ -0,0 +1,154 @@
+// @vitest-environment happy-dom
+// Run: ORCA_REVIEW_RAIL_BENCH=1 pnpm test src/renderer/src/components/editor/rich-markdown-review-rail-benchmark.test.ts
+import { expect, it, vi } from 'vitest'
+import { Editor as TiptapEditor } from '@tiptap/core'
+import { createRichMarkdownExtensions } from './rich-markdown-extensions'
+import { createRichMarkdownEditorCodec } from './rich-markdown-source-transport'
+import { measureRichMarkdownReviewNotePositions } from './rich-markdown-review-note-positioning'
+
+// Baseline measurement body from the parent revision, before sharing source blocks.
+import type { Editor } from '@tiptap/react'
+import type { DiffComment } from '../../../../shared/diff-comment-types'
+import {
+  buildRichMarkdownCommentBlocks,
+  getRichMarkdownCommentAnchorTop
+} from './rich-markdown-review-annotations'
+import {
+  stackRichMarkdownReviewNotePositions,
+  type RichMarkdownReviewNotePosition
+} from './rich-markdown-review-note-layout'
+
+type MeasureRichMarkdownReviewNotePositionsOptions = {
+  container: HTMLDivElement
+  editor: Editor
+  markdownComments: DiffComment[]
+  markdownSourceLineOffset: number
+}
+
+function measureBaseline({
+  container,
+  editor,
+  markdownComments,
+  markdownSourceLineOffset
+}: MeasureRichMarkdownReviewNotePositionsOptions): RichMarkdownReviewNotePosition[] {
+  const containerRect = container.getBoundingClientRect()
+  const blocks = buildRichMarkdownCommentBlocks(editor)
+  const nextPositions = markdownComments
+    .map((comment): RichMarkdownReviewNotePosition | null => {
+      const bodyLineNumber = Math.max(1, comment.lineNumber - markdownSourceLineOffset)
+      const block = blocks.find(
+        (candidate) => candidate.startLine <= bodyLineNumber && bodyLineNumber <= candidate.endLine
+      )
+      if (!block) {
+        return null
+      }
+      const top = getRichMarkdownCommentAnchorTop(
+        editor,
+        comment,
+        block,
+        containerRect,
+        container.scrollTop,
+        markdownSourceLineOffset
+      )
+      return top === null ? null : { comment, top }
+    })
+    .filter((position): position is RichMarkdownReviewNotePosition => position !== null)
+  return stackRichMarkdownReviewNotePositions(
+    nextPositions,
+    measureReviewNoteHeights(container, nextPositions)
+  )
+}
+
+function measureReviewNoteHeights(
+  container: HTMLDivElement,
+  positions: RichMarkdownReviewNotePosition[]
+): Map<string, number> {
+  const measuredHeights = new Map<string, number>()
+  for (const pos of positions) {
+    const el = container.querySelector(`[data-rich-markdown-review-note-id="${pos.comment.id}"]`)
+    if (el) {
+      measuredHeights.set(pos.comment.id, el.getBoundingClientRect().height)
+    }
+  }
+  return measuredHeights
+}
+
+it.skipIf(process.env.ORCA_REVIEW_RAIL_BENCH !== '1')(
+  'benchmarks full review rail measurements',
+  () => {
+    for (const blockCount of [250, 1000]) {
+      const editor = new TiptapEditor({
+        element: document.createElement('div'),
+        extensions: createRichMarkdownExtensions({ codec: createRichMarkdownEditorCodec() }),
+        content: {
+          type: 'doc',
+          content: Array.from({ length: blockCount }, (_, index) => ({
+            type: 'paragraph',
+            content: [{ type: 'text', text: `Paragraph ${index} with reviewable content.` }]
+          }))
+        }
+      })
+      try {
+        vi.spyOn(editor.view, 'coordsAtPos').mockReturnValue({
+          top: 100,
+          bottom: 120,
+          left: 0,
+          right: 10
+        })
+        const container = document.createElement('div')
+        const markdownComments: DiffComment[] = Array.from({ length: 5 }, (_, index) => ({
+          id: `note-${index}`,
+          worktreeId: 'workspace',
+          filePath: 'notes.md',
+          source: 'markdown',
+          lineNumber: 1 + index * 40,
+          body: 'Review',
+          createdAt: index,
+          side: 'modified'
+        }))
+        const args = { editor, container, markdownComments, markdownSourceLineOffset: 0 }
+        const serialize = vi.spyOn(editor.markdown!, 'serialize')
+        const baseline = measureBaseline(args)
+        const baselineCalls = serialize.mock.calls.length
+        serialize.mockClear()
+        expect(measureRichMarkdownReviewNotePositions(args)).toEqual(baseline)
+        const coldCalls = serialize.mock.calls.length
+        serialize.mockClear()
+        expect(measureRichMarkdownReviewNotePositions(args)).toEqual(baseline)
+        const warmCalls = serialize.mock.calls.length
+        serialize.mockRestore()
+        const time = (run: () => unknown) => {
+          const start = performance.now()
+          for (let index = 0; index < 20; index++) {
+            run()
+          }
+          return (performance.now() - start) / 20
+        }
+        const before: number[] = []
+        const after: number[] = []
+        for (let round = 0; round < 5; round++) {
+          before.push(time(() => measureBaseline(args)))
+          after.push(time(() => measureRichMarkdownReviewNotePositions(args)))
+        }
+        const median = (values: number[]) => values.sort((a, b) => a - b)[2]!
+        const result = {
+          blockCount,
+          comments: markdownComments.length,
+          beforeMs: median(before),
+          afterMs: median(after),
+          baselineCalls,
+          coldCalls,
+          warmCalls
+        }
+        process.stdout.write(`${JSON.stringify(result)}\n`)
+        expect(baselineCalls).toBe((2 * blockCount - 1) * 6)
+        expect(coldCalls).toBe(2 * blockCount - 1)
+        expect(warmCalls).toBe(0)
+      } finally {
+        editor.destroy()
+        vi.restoreAllMocks()
+      }
+    }
+  },
+  120_000
+)
diff --git a/src/renderer/src/components/editor/rich-markdown-review-rail-blocks.test.ts b/src/renderer/src/components/editor/rich-markdown-review-rail-blocks.test.ts
new file mode 100644
index 00000000000..18c00a47fb5
--- /dev/null
+++ b/src/renderer/src/components/editor/rich-markdown-review-rail-blocks.test.ts
@@ -0,0 +1,139 @@
+// @vitest-environment happy-dom
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { Editor, type JSONContent } from '@tiptap/core'
+import type { DiffComment } from '../../../../shared/diff-comment-types'
+import { createRichMarkdownExtensions } from './rich-markdown-extensions'
+import { createRichMarkdownEditorCodec } from './rich-markdown-source-transport'
+import { buildRichMarkdownCommentBlocks } from './rich-markdown-review-annotations'
+import { getRichMarkdownReviewRailBlocks } from './rich-markdown-review-rail-blocks'
+import { measureRichMarkdownReviewNotePositions } from './rich-markdown-review-note-positioning'
+
+const editors: Editor[] = []
+
+function createEditor(
+  content: string | JSONContent = '# Heading\n\nFirst paragraph\n\n- One\n- Two'
+) {
+  const editor = new Editor({
+    element: document.createElement('div'),
+    extensions: createRichMarkdownExtensions({ codec: createRichMarkdownEditorCodec() }),
+    content,
+    ...(typeof content === 'string' ? { contentType: 'markdown' as const } : {})
+  })
+  editors.push(editor)
+  // Settle the trailing-node plugin before measuring selection-only transactions.
+  editor.view.dispatch(editor.state.tr.setMeta('addToHistory', false))
+  return editor
+}
+
+afterEach(() => {
+  for (const editor of editors.splice(0)) {
+    editor.destroy()
+  }
+  vi.restoreAllMocks()
+})
+
+describe('review rail source block reuse', () => {
+  it.each([
+    '```ts\nconst value = 1\n\nvalue++\n```\n\nAfter code',
+    '| First | Second |\n| --- | --- |\n| one | two |\n\nAfter table',
+    '<details><summary>Toggle</summary>\n\nInside\n\n</details>\n\nAfter toggle'
+  ])('preserves multiline block boundaries for %s', (source) => {
+    const editor = createEditor(source)
+    expect(getRichMarkdownReviewRailBlocks(editor)).toEqual(buildRichMarkdownCommentBlocks(editor))
+  })
+
+  it('preserves block lines and reuses them after selection-only transactions', () => {
+    const editor = createEditor()
+    const expected = buildRichMarkdownCommentBlocks(editor)
+    const serialize = vi.spyOn(editor.markdown!, 'serialize')
+    const blocks = getRichMarkdownReviewRailBlocks(editor)
+    expect(blocks).toEqual(expected)
+    expect(serialize).toHaveBeenCalledTimes(2 * editor.state.doc.childCount - 1)
+    serialize.mockClear()
+    editor.commands.setTextSelection(3)
+    expect(getRichMarkdownReviewRailBlocks(editor)).toBe(blocks)
+    expect(serialize).not.toHaveBeenCalled()
+  })
+
+  it('rebuilds after edits and undo while keeping editors isolated', () => {
+    const editor = createEditor()
+    const original = getRichMarkdownReviewRailBlocks(editor)
+    editor.commands.insertContentAt(1, 'changed\ntext')
+    const changed = getRichMarkdownReviewRailBlocks(editor)
+    expect(changed).not.toBe(original)
+    expect(changed).toEqual(buildRichMarkdownCommentBlocks(editor))
+    editor.commands.undo()
+    expect(getRichMarkdownReviewRailBlocks(editor)).toEqual(original)
+    expect(getRichMarkdownReviewRailBlocks(createEditor())).not.toBe(original)
+  })
+
+  it('invalidates an in-place serializer replacement and a manager replacement', () => {
+    const editor = createEditor()
+    const original = getRichMarkdownReviewRailBlocks(editor)
+    const serialize = editor.markdown!.serialize.bind(editor.markdown)
+    vi.spyOn(editor.markdown!, 'serialize').mockImplementation(
+      (content) => `${serialize(content)}\nextra line`
+    )
+    const changed = getRichMarkdownReviewRailBlocks(editor)
+    expect(changed).not.toEqual(original)
+    expect(changed).toEqual(buildRichMarkdownCommentBlocks(editor))
+    editor.markdown = createEditor().markdown
+    expect(getRichMarkdownReviewRailBlocks(editor)).toEqual(original)
+  })
+
+  it('does not reuse fallback lines after a missing serializer becomes available', () => {
+    const editor = createEditor()
+    const markdown = editor.markdown
+    editor.markdown = undefined
+    const fallback = getRichMarkdownReviewRailBlocks(editor)
+    expect(fallback).toEqual(buildRichMarkdownCommentBlocks(editor))
+    editor.markdown = markdown
+    expect(getRichMarkdownReviewRailBlocks(editor)).not.toEqual(fallback)
+    expect(getRichMarkdownReviewRailBlocks(editor)).toEqual(buildRichMarkdownCommentBlocks(editor))
+  })
+
+  it('avoids serialization for every comment and repeated scroll while refreshing geometry', () => {
+    const editor = createEditor()
+    let sourceTop = 100
+    const coords = vi.spyOn(editor.view, 'coordsAtPos').mockImplementation(() => ({
+      top: sourceTop,
+      bottom: sourceTop + 20,
+      left: 0,
+      right: 10
+    }))
+    const container = document.createElement('div')
+    const comment: DiffComment = {
+      id: 'note',
+      worktreeId: 'workspace',
+      filePath: 'notes.md',
+      source: 'markdown',
+      lineNumber: 1,
+      body: 'Review',
+      createdAt: 1,
+      side: 'modified'
+    }
+    const markdownComments = Array.from({ length: 5 }, (_, index) => ({
+      ...comment,
+      id: `note-${index}`,
+      selectedText: index === 0 ? 'Heading' : undefined
+    }))
+    const serialize = vi.spyOn(editor.markdown!, 'serialize')
+    const measure = () =>
+      measureRichMarkdownReviewNotePositions({
+        editor,
+        container,
+        markdownComments,
+        markdownSourceLineOffset: 0
+      })
+    expect(measure()[0]?.top).toBe(100)
+    expect(serialize).toHaveBeenCalledTimes(2 * editor.state.doc.childCount - 1)
+    serialize.mockClear()
+    sourceTop = 200
+    container.scrollTop = 30
+    for (let index = 0; index < 60; index++) {
+      expect(measure()[0]?.top).toBe(230)
+    }
+    expect(serialize).not.toHaveBeenCalled()
+    expect(coords).toHaveBeenCalledTimes(61 * markdownComments.length)
+  })
+})
diff --git a/src/renderer/src/components/editor/rich-markdown-review-rail-blocks.ts b/src/renderer/src/components/editor/rich-markdown-review-rail-blocks.ts
new file mode 100644
index 00000000000..35dd1bb9eb5
--- /dev/null
+++ b/src/renderer/src/components/editor/rich-markdown-review-rail-blocks.ts
@@ -0,0 +1,31 @@
+import type { Editor } from '@tiptap/core'
+import {
+  buildRichMarkdownCommentBlocks,
+  type RichMarkdownCommentBlock
+} from './rich-markdown-review-annotations'
+
+type ReviewRailBlocks = {
+  doc: Editor['state']['doc']
+  markdown: Editor['markdown']
+  serialize: NonNullable<Editor['markdown']>['serialize'] | undefined
+  blocks: readonly RichMarkdownCommentBlock[]
+}
+
+// Keep only the current document per editor; scrolling changes geometry, not source lines.
+const blocksByEditor = new WeakMap<Editor, ReviewRailBlocks>()
+
+export function getRichMarkdownReviewRailBlocks(
+  editor: Editor
+): readonly RichMarkdownCommentBlock[] {
+  const doc = editor.state.doc
+  const markdown = editor.markdown
+  const serialize = markdown?.serialize
+  const cached = blocksByEditor.get(editor)
+  if (cached?.doc === doc && cached.markdown === markdown && cached.serialize === serialize) {
+    return cached.blocks
+  }
+
+  const blocks = buildRichMarkdownCommentBlocks(editor)
+  blocksByEditor.set(editor, { doc, markdown, serialize, blocks })
+  return blocks
+}