perf(editor): skip Markdown classification beyond the hard render cap (#34798)

Above the 1 MiB override cap a Markdown file can never render rich, so
skip the unsupported-syntax scan and keep those documents out of the
eligibility cache.

Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>

src/renderer/src/components/editor/markdown-rich-mode-eligibility-cache.ts

@@ -4,6 +4,7 @@ import {
   type MarkdownRichModeEligibility,
   type MarkdownRichModeEligibilityDecision
 } from './markdown-rich-mode'
+import { exceedsMarkdownRenderOverrideSizeLimit } from './markdown-rich-size-limit'
 
 type EligibilityCacheEntry = {
   content: string
@@ -46,6 +47,10 @@ function getCachedMarkdownRichModeEligibilityDecision(params: {
   }
 
   const decision = getMarkdownRichModeEligibilityDecision({ content, sizeOverridden })
+  // Don't retain hard-cap documents; checked after lookup so cache hits skip the UTF-8 probe.
+  if (decision.exceedsSizeLimit && exceedsMarkdownRenderOverrideSizeLimit(content)) {
+    return decision
+  }
   entries.unshift({ content, sizeOverridden, decision })
   if (entries.length > MAX_ENTRIES) {
     entries.length = MAX_ENTRIES

src/renderer/src/components/editor/markdown-rich-mode.test.ts

@@ -1,5 +1,6 @@
 import { afterEach, describe, expect, it, vi } from 'vitest'
 import * as roundTrip from './markdown-round-trip'
+import { MARKDOWN_RENDER_OVERRIDE_MAX_SIZE_BYTES } from './markdown-rich-size-limit'
 import { RICH_MARKDOWN_MAX_SIZE_BYTES } from '../../../../shared/constants'
 import {
   getMarkdownRichModeEligibility,
@@ -207,6 +208,24 @@ describe('getMarkdownRichModeUnsupportedMessage', () => {
       unsupportedMessage: expect.any(String)
     })
   })
+
+  it.each([false, true])(
+    'reports only the size limit beyond the hard render cap, override=%s',
+    (sizeOverridden) => {
+      const content = `${'a'.repeat(MARKDOWN_RENDER_OVERRIDE_MAX_SIZE_BYTES)}\n[ref]: /docs\n`
+
+      const result = getMarkdownRichModeEligibility({ content, sizeOverridden })
+      expect(result).toEqual({
+        exceedsSizeLimit: true,
+        unsupportedMessage: null
+      })
+
+      expect(
+        getMarkdownRichModeEligibility({ content: '[ref]: /docs', sizeOverridden })
+          .unsupportedMessage
+      ).not.toBeNull()
+    }
+  )
 })
 
 const decide = (content: string) =>

src/renderer/src/components/editor/markdown-rich-mode.ts

@@ -5,7 +5,10 @@ import {
   getRichMarkdownRoundTripOutput
 } from './markdown-round-trip'
 import { extractFrontMatter } from './markdown-frontmatter'
-import { canRenderMarkdownAtSize } from './markdown-rich-size-limit'
+import {
+  canRenderMarkdownAtSize,
+  exceedsMarkdownRenderOverrideSizeLimit
+} from './markdown-rich-size-limit'
 import { translate } from '@/i18n/i18n'
 import { encodeRawMarkdownHtmlForRichEditor } from './raw-markdown-html'
 import { createRichMarkdownEditorCodec } from './rich-markdown-source-transport'
@@ -142,6 +145,10 @@ export function getMarkdownRichModeEligibilityDecision({
   content: string
   sizeOverridden: boolean
 }): MarkdownRichModeEligibilityDecision {
+  // Past the hard cap neither mode renders rich, so the unsupported-syntax scan is moot.
+  if (exceedsMarkdownRenderOverrideSizeLimit(content)) {
+    return { exceedsSizeLimit: true, unsupportedReason: null }
+  }
   return {
     exceedsSizeLimit: !canRenderMarkdownAtSize(content, sizeOverridden),
     unsupportedReason: getMarkdownRichModeUnsupportedReason(content)