fix(files): collapse blank-line runs to markdown standard (no empty-paragraph explosion / reflow) (#6198)

parseMarkdownToDoc now strips ALL top-level empty paragraphs (leading, interior, trailing),
not just trailing. A run of blank lines between blocks is insignificant in markdown
(CommonMark collapses it), but @tiptap/markdown reconstructs one empty paragraph per blank
line — which made the mounted editor render vertical gaps that exist nowhere else the file
is viewed (GitHub, download, our own static preview), let a pathological blank run explode
into thousands of empty nodes, and caused the visible reflow on open (static preview
collapses empty <p>; the live editor gives each a trailing-break line). Collapsing on parse
keeps normal one-blank-line spacing, matches every standard renderer, and stays idempotent
so the round-trip-safety probe still reaches a fixed point (files stay editable; existing
files normalize on next cold-open + save). Serializer is intentionally NOT changed — a
global blank-run collapse there would corrupt blank lines inside fenced code blocks.

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/rich-markdown-editor/markdown-fidelity.ts

@@ -172,9 +172,14 @@ function stripEmptyListItemLines(markdown: string): string {
  * Cleans up serializer output: drops empty list-item marker lines that would otherwise corrupt on
  * round-trip ({@link stripEmptyListItemLines}), restores callout markers the serializer
  * backslash-escapes (`> \[!NOTE\]` → `> [!NOTE]`), and collapses trailing blank lines to a single
- * newline. The table serializer's spurious surrounding blank lines are trimmed at the source
- * (PipeSafeTable), so no global leading-newline strip is needed here — avoiding clobbering content
- * that legitimately begins with whitespace.
+ * newline. Interior blank runs are NOT collapsed here — blank lines inside a fenced code block (or a
+ * verbatim raw-markdown-snippet) are significant, and a global collapse would corrupt them. Spurious
+ * interior blank runs between top-level blocks are removed upstream instead, by
+ * {@link parseMarkdownToDoc} stripping empty paragraphs, so a doc that has been through the editor
+ * never serializes with an interior blank run outside code in the first place. The table serializer's
+ * spurious surrounding blank lines are trimmed at the source (PipeSafeTable), so no global
+ * leading-newline strip is needed here — avoiding clobbering content that legitimately begins with
+ * whitespace.
  */
 export function postProcessSerializedMarkdown(markdown: string): string {
   return collapseAutolinkedUrls(

apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/rich-markdown-editor/markdown-parse.test.ts

@@ -7,6 +7,10 @@ import { createMarkdownContentExtensions } from './extensions'
 import { parseMarkdownToDoc, serializeMarkdownBody, splitMarkdownBlocks } from './markdown-parse'
 import { isRoundTripSafe } from './round-trip-safety'
 
+/** Mirror of the production `isEmptyParagraph` (not exported): the shape a blank line reconstructs to. */
+const isEmptyPara = (n: { type?: string; content?: unknown[] }): boolean =>
+  n.type === 'paragraph' && !n.content?.length
+
 let editor: Editor | null = null
 afterEach(() => {
   editor?.destroy()
@@ -59,12 +63,6 @@ const CASES: Array<[string, string]> = [
     '1. First\n  - sub bullet\n  - another\n  1. deep ordered\n  2. item\n2. Second',
   ],
   ['heading-separated sections', '# A\n\nalpha\n\n## B\n\nbeta\n\n## C\n\ngamma'],
-  // Blank-line spacing: `@tiptap/markdown` reconstructs empty paragraphs from runs of blank lines, so
-  // the chunker must reinsert them or a saved blank line vanishes on reload. See the dedicated
-  // "empty paragraphs" suite below for the exact whole-document-parser parity.
-  ['one empty paragraph between paragraphs', 'first\n\n\n\nsecond'],
-  ['two empty paragraphs between paragraphs', 'first\n\n\n\n\n\nsecond'],
-  ['empty paragraphs between headings and text', '# A\n\n\n\nalpha\n\n\n\n## B'],
 ]
 
 describe('parseMarkdownToDoc (chunked)', () => {
@@ -93,63 +91,62 @@ describe('parseMarkdownToDoc (chunked)', () => {
     expect(splitMarkdownBlocks('\n\n  \n')).toEqual([])
   })
 
-  // The chunker used to drop empty paragraphs (visual blank lines between blocks) that the whole-document
-  // parser preserves, so a saved blank line silently vanished on the next load. These assert the chunked
-  // parse reconstructs the SAME empty-paragraph structure the whole-document parser does — at document
-  // edges and between blocks, for one or many blank lines, and around lists.
-  describe('empty paragraphs (blank-line spacing) match the whole-document parser', () => {
-    /** Block-type shape of a doc, `∅` for an empty paragraph, normalized through the editor. */
-    function shapeOf(md: string, parse: 'chunked' | 'whole'): string {
-      editor = new Editor({ extensions: createMarkdownContentExtensions() })
-      if (parse === 'whole') editor.commands.setContent(md, { contentType: 'markdown' })
-      else editor.commands.setContent(parseMarkdownToDoc(md), { contentType: 'json' })
-      const shape = (editor.getJSON().content ?? [])
-        .map((n) => (n.type === 'paragraph' && !n.content?.length ? '∅' : n.type))
+  // Asserts the collapse documented on `stripEmptyParagraphs` — at document edges, between blocks, for
+  // one or many blank lines, and around lists. (Blank runs are insignificant in markdown, so a collapsed
+  // file renders identically everywhere it's viewed; the pathological case is a run of thousands.)
+  describe('collapses blank-line runs to markdown-standard spacing', () => {
+    /** Block-type shape of a doc after `parseMarkdownToDoc`, `∅` for any surviving empty paragraph. */
+    function shapeOf(md: string): string {
+      return (parseMarkdownToDoc(md).content ?? [])
+        .map((n) => (isEmptyPara(n) ? '∅' : n.type))
         .join(',')
-      editor.destroy()
-      editor = null
-      return shape
     }
 
     it.each([
-      ['one empty between paragraphs', 'a\n\n\n\nb'],
-      ['two empties between paragraphs', 'a\n\n\n\n\n\nb'],
-      ['three empties between paragraphs', 'a\n\n\n\n\n\n\n\nb'],
-      ['even blank-line gap (rounds down)', 'a\n\n\n\n\nb'],
-      ['leading empties', '\n\n\n\na'],
-      ['leading + between', '\n\n\na\n\n\n\nb'],
-      ['empties between a heading and text', '# H\n\n\n\ntext'],
-      ['empties after a tight list', '- a\n- b\n\n\n\ntext'],
-      ['empties before a tight list', 'text\n\n\n\n- a\n- b'],
-      // Line-ending variants: the whole-vs-chunked routing must normalize first, or a `\r`-only body
-      // skips the empty-paragraph guard and is chunked (dropping the empties this fix restores).
-      ['CRLF between empties', 'a\r\n\r\n\r\n\r\nb'],
-      ['CR-only (classic Mac) between empties', 'a\r\r\r\rb'],
-    ])('chunked matches whole-doc: %s', (_label, md) => {
-      expect(shapeOf(md, 'chunked')).toBe(shapeOf(md, 'whole'))
+      ['one blank gap between paragraphs', 'a\n\n\n\nb', 'paragraph,paragraph'],
+      ['many blank lines between paragraphs', 'a\n\n\n\n\n\n\n\nb', 'paragraph,paragraph'],
+      ['leading blank lines', '\n\n\n\na', 'paragraph'],
+      ['leading + interior', '\n\n\na\n\n\n\nb', 'paragraph,paragraph'],
+      ['blank gap between a heading and text', '# H\n\n\n\ntext', 'heading,paragraph'],
+      ['blank gap after a tight list', '- a\n- b\n\n\n\ntext', 'bulletList,paragraph'],
+      ['blank gap before a tight list', 'text\n\n\n\n- a\n- b', 'paragraph,bulletList'],
+      // Line-ending variants normalize first, so `\r`-only / CRLF blank runs collapse identically.
+      ['CRLF between blocks', 'a\r\n\r\n\r\n\r\nb', 'paragraph,paragraph'],
+      ['CR-only (classic Mac) between blocks', 'a\r\r\r\rb', 'paragraph,paragraph'],
+    ])('collapses to no empty paragraphs: %s', (_label, md, expected) => {
+      expect(shapeOf(md)).toBe(expected)
+    })
+
+    it('a pathological blank run does not explode into empty paragraph nodes', () => {
+      // The production incident: an agent/paste artifact with a huge blank run became ~1959 empty
+      // paragraphs baked into the doc. Collapsing on parse neutralizes any such source.
+      const body = `Para A${'\n'.repeat(4000)}Para B`
+      const content = parseMarkdownToDoc(body).content ?? []
+      expect(content.filter(isEmptyPara).length).toBe(0)
+      expect(content.map((n) => n.type)).toEqual(['paragraph', 'paragraph'])
     })
   })
 
-  // Regression: a file ending in a blank line (a trailing empty paragraph) must stay EDITABLE. Such an
-  // empty paragraph can't be serialized stably (postProcess collapses trailing newlines), so the parser
-  // strips it — keeping the doc round-trip-safe/idempotent instead of flipping the file read-only.
-  describe('trailing blank lines stay editable (regression)', () => {
+  // Regression: a file with blank lines (leading, interior, or trailing) must stay EDITABLE. Collapsing
+  // blank runs keeps serialize→parse idempotent, so the round-trip-safety probe reaches a fixed point
+  // instead of flipping the file read-only.
+  describe('blank lines stay editable (regression)', () => {
     it.each([
       ['plain paragraph', 'abc\n\n'],
       ['heading + text', '# Title\n\nSome text\n\n'],
       ['three trailing newlines', 'hello\n\n\n'],
       ['two paragraphs', 'para one\n\npara two\n\n'],
-      ['interior empties + trailing', 'a\n\n\n\nb\n\n'],
-    ])('a file ending in a blank line is round-trip-safe: %s', (_label, md) => {
+      ['interior blank run + trailing', 'a\n\n\n\nb\n\n'],
+    ])('a file with blank lines is round-trip-safe: %s', (_label, md) => {
       expect(isRoundTripSafe(md)).toBe(true)
     })
 
-    it('strips the trailing empty paragraph but keeps interior ones', () => {
+    it('removes only structurally-empty paragraphs — a paragraph with content survives', () => {
+      // The shape suite above already proves leading/interior/trailing blank runs collapse to zero empty
+      // paragraphs; this pins the complementary guarantee — a real (non-empty) paragraph is never dropped.
       const trailing = parseMarkdownToDoc('abc\n\n').content ?? []
       expect(trailing.at(-1)?.type).toBe('paragraph')
-      expect(trailing.at(-1)?.content?.length ?? 0).toBeGreaterThan(0)
-      const interior = parseMarkdownToDoc('a\n\n\n\nb').content ?? []
-      expect(interior.some((n) => n.type === 'paragraph' && !n.content?.length)).toBe(true)
+      expect(isEmptyPara(trailing.at(-1) ?? {})).toBe(false)
     })
   })
 

apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/rich-markdown-editor/markdown-parse.ts

@@ -47,20 +47,6 @@ const FENCE_CLOSE = /^ {0,3}(`{3,}|~{3,})[ \t]*$/
 const LIST_MARKER = /^[ ]{0,3}(?:[-*+]|\d+[.)])\s/
 const BLOCKQUOTE = /^[ ]{0,3}>/
 
-/**
- * Blank-line spacing that `@tiptap/markdown` reconstructs as *interior* or *leading* empty paragraphs —
- * a run of two or more blank lines somewhere, or blank line(s) at the document's leading edge. `[^\S\n]`
- * matches horizontal whitespace, so a "blank" line may carry spaces/tabs. This is only ever tested
- * against the `\r`-normalized body ({@link parseMarkdownToDoc}), so no CRLF handling is needed here.
- *
- * A *single* trailing blank line is deliberately not matched — purely to avoid routing an otherwise-plain
- * file to the slower whole-document parser. Correctness does not depend on it: {@link parseMarkdownToDoc}
- * strips trailing empty paragraphs on *both* parse paths ({@link stripTrailingEmptyParagraphs}), so
- * serialize→parse stays idempotent regardless of which parser ran. (A trailing run of two or more blanks
- * still matches the interior alternative — harmless, since the strip cleans it either way.)
- */
-const EMPTY_PARAGRAPH_SPACING = /\n[^\S\n]*\n[^\S\n]*\n|^[^\S\n]*\n[^\S\n]*\n/
-
 /**
  * Split a markdown body into top-level blocks that can each be parsed independently and reassembled
  * without changing meaning. Blank lines separate candidate groups (fenced code blocks stay atomic),
@@ -135,21 +121,20 @@ export function splitMarkdownBlocks(body: string): string[] {
  * Documents whose constructs span blocks ({@link NON_CHUNKABLE}) parse whole, and any failure falls
  * back to a single whole-document parse, so correctness never depends on the splitter.
  *
- * Blank-line spacing ({@link EMPTY_PARAGRAPH_SPACING}) also parses whole: the chunker parses each block
- * stripped of the blank lines between them, so it drops the empty paragraphs `@tiptap/markdown` builds
- * from runs of blank lines — a saved visual blank line would silently vanish on reload. Whether a gap
- * yields an empty paragraph is a global, block-type-dependent decision (kept between two paragraphs,
- * dropped after a heading), so it can't be reconstructed block-locally; these documents parse whole for
- * exact fidelity. Ordinary single-blank-line separation still takes the fast chunked path.
+ * Runs of blank lines take the fast chunked path too: the chunker parses each block stripped of the
+ * blank lines between them, which drops the empty paragraphs `@tiptap/markdown` reconstructs from a
+ * blank run — exactly what {@link stripEmptyParagraphs} does to the whole-parse output anyway. A blank
+ * run between blocks is insignificant in markdown, so collapsing it is the intended normalization (see
+ * {@link stripEmptyParagraphs}), and both parse paths converge on the same empty-paragraph-free result.
  */
 export function parseMarkdownToDoc(body: string): JSONContent {
   const manager = markdownManager()
-  // Normalize line endings up front so the routing guards see the same `\n` the chunker and parser
-  // do — the guards' `\n`-anchored tests would otherwise miss a classic `\r`-only body (its blank
-  // lines are `\r`), routing it to the chunker that then drops its empty paragraphs.
+  // Normalize line endings up front so {@link NON_CHUNKABLE}'s `\n`-anchored tests see the same `\n`
+  // the chunker and parser do — a classic `\r`-only body would otherwise slip past the reference-def /
+  // block-HTML guard and be chunked, shattering a construct that must parse whole.
   const normalized = body.replace(/\r\n?/g, '\n')
   let doc: JSONContent
-  if (NON_CHUNKABLE.test(normalized) || EMPTY_PARAGRAPH_SPACING.test(normalized)) {
+  if (NON_CHUNKABLE.test(normalized)) {
     doc = manager.parse(normalized)
   } else {
     try {
@@ -163,7 +148,7 @@ export function parseMarkdownToDoc(body: string): JSONContent {
       doc = manager.parse(normalized)
     }
   }
-  return stripTrailingEmptyParagraphs(doc)
+  return stripEmptyParagraphs(doc)
 }
 
 /** An empty paragraph node — the shape a blank line reconstructs to (no content, or `content: []`). */
@@ -172,19 +157,26 @@ function isEmptyParagraph(node: JSONContent): boolean {
 }
 
 /**
- * Drop trailing empty paragraphs from a parsed doc. {@link postProcessSerializedMarkdown} collapses
- * trailing blank lines to a single newline, so a trailing empty paragraph can never round-trip — the
- * whole-document parser reconstructs one from a file ending in a blank line, but keeping it makes
- * serialize→parse non-idempotent, which flips the file read-only via the round-trip-safety probe.
- * Leading/interior empty paragraphs are untouched (postProcess never strips those). TipTap re-adds its
- * own trailing filler paragraph on `setContent`, so the editor still has a place to type.
+ * Drop ALL top-level empty paragraphs from a parsed doc — leading, interior, and trailing. In markdown
+ * a run of blank lines between blocks is insignificant (CommonMark collapses it), so `@tiptap/markdown`
+ * reconstructing each blank as an empty paragraph node is not fidelity: it makes the editor render the
+ * file differently from every standard renderer (GitHub, the download, our own static preview), and a
+ * pathological blank run (an agent/paste artifact) explodes into thousands of empty nodes that persist
+ * forever and reflow the doc on open. Collapsing them here keeps normal single-blank-line block spacing
+ * while removing the spurious gaps, and stays idempotent so the round-trip-safety probe still passes: a
+ * doc parsed this way has no empty paragraphs, so re-serializing it never re-emits an interior blank run
+ * (the serializer is intentionally left alone — a blank line inside a fenced code block IS significant),
+ * and a second parse is a fixed point. Only TOP-LEVEL paragraphs are touched, so blank lines that carry
+ * meaning inside a construct (e.g. a loose list) are left to the block parser. TipTap re-adds its own
+ * trailing filler paragraph on `setContent`, so the editor still has a place to type.
  */
-function stripTrailingEmptyParagraphs(doc: JSONContent): JSONContent {
+function stripEmptyParagraphs(doc: JSONContent): JSONContent {
   const content = doc.content
   if (!content || content.length === 0) return doc
-  let end = content.length
-  while (end > 0 && isEmptyParagraph(content[end - 1])) end--
-  return end === content.length ? doc : { ...doc, content: content.slice(0, end) }
+  // The dominant (chunked) parse already emits no top-level empty paragraphs, so scan before allocating:
+  // return the doc untouched — no array copy — unless there is actually something to strip.
+  if (!content.some(isEmptyParagraph)) return doc
+  return { ...doc, content: content.filter((node) => !isEmptyParagraph(node)) }
 }
 
 /**