diff --git a/services/web/frontend/js/features/source-editor/lezer-typst/tokens.mjs b/services/web/frontend/js/features/source-editor/lezer-typst/tokens.mjs
index bdcadf8e1a..26710b6ed3 100644
--- a/services/web/frontend/js/features/source-editor/lezer-typst/tokens.mjs
+++ b/services/web/frontend/js/features/source-editor/lezer-typst/tokens.mjs
@@ -56,8 +56,16 @@ export const headingTokenizer = new ExternalTokenizer(
 // Using an external token (terminal) instead of grammar sub-items avoids
 // LALR(1) conflicts: any token shared between headingTitleItem and document-
 // level item causes the automaton to merge the two contexts.
+//
+// contextual: true — the tokenizer checks stack.canShift(HeadingTitle) before
+// doing anything, so it ONLY fires in the LR state reached after HeadingMark.
+// With contextual: false, Lezer calls the tokenizer speculatively at any
+// position where HeadingTitle is *conceivably* valid (due to LALR state
+// merging), which can cause whole lines of body text to be consumed as
+// HeadingTitle tokens and styled as headings.
 export const headingTitleTokenizer = new ExternalTokenizer(
-  (input, _stack) => {
+  (input, stack) => {
+    if (!stack.canShift(HeadingTitle)) return
     let hasContent = false
     while (input.next !== -1 && input.next !== NEWLINE) {
       // Stop before a line comment (//) or block comment (/*) so that
@@ -69,7 +77,7 @@ export const headingTitleTokenizer = new ExternalTokenizer(
     }
     if (hasContent) input.acceptToken(HeadingTitle)
   },
-  { contextual: false }
+  { contextual: true }
 )
 
 // ── rawTokenizer ────────────────────────────────────────────────────────
diff --git a/services/web/frontend/js/ide/log-parser/quarto-log-parser.ts b/services/web/frontend/js/ide/log-parser/quarto-log-parser.ts
index a1dbdfada0..3078285a17 100644
--- a/services/web/frontend/js/ide/log-parser/quarto-log-parser.ts
+++ b/services/web/frontend/js/ide/log-parser/quarto-log-parser.ts
@@ -58,6 +58,11 @@ const PY_MODULE_TO_PACKAGE: Record<string, string> = {
 }
 // A typst diagnostic location line: `  ┌─ main.typ:5:10` / `  --> main.typ:5:10`
 const TYPST_LOCATION_REGEX = /(?:[┌╭]─|-->)\s*(.+?):(\d+):(\d+)/
+// Quarto schema-validation location line emitted after `ERROR: In file <f>`:
+//   (line 6, columns 24--27) Field "section-numbering" has value …
+const QUARTO_SCHEMA_LOC_REGEX = /^\(line (\d+), columns? \d+(?:--\d+)?\)\s+(.*)/
+// Extracts the filename from an `ERROR: In file <filename>` message.
+const QUARTO_IN_FILE_REGEX = /^In file (.+)$/
 
 function stripAnsi(line: string): string {
   return line.replace(ANSI_REGEX, '')
@@ -67,7 +72,8 @@ function isDiagnosticStart(trimmed: string): boolean {
   return (
     LOWER_DIAG_REGEX.test(trimmed) ||
     UPPER_DIAG_REGEX.test(trimmed) ||
-    PANDOC_REGEX.test(trimmed)
+    PANDOC_REGEX.test(trimmed) ||
+    QUARTO_SCHEMA_LOC_REGEX.test(trimmed)
   )
 }
 
@@ -119,14 +125,48 @@ export default function parseQuartoLog(rawLog: string): ParseResult {
       continue
     }
 
+    // Quarto schema-validation errors span two lines:
+    //   ERROR: In file main.qmd           ← stores pendingLocation.file
+    //   (line 6, columns 24--27) Field … ← this line carries line + message
+    let m: RegExpMatchArray | null
+    if ((m = trimmed.match(QUARTO_SCHEMA_LOC_REGEX))) {
+      const logLine = parseInt(m[1], 10)
+      const msg = m[2].trim()
+      let content = clean
+      let j = i + 1
+      for (; j < lines.length; j++) {
+        const next = stripAnsi(lines[j])
+        if (next.trim() === '') break
+        if (isDiagnosticStart(next.trimStart())) break
+        content += '\n' + next
+      }
+      i = j - 1
+      data.push({
+        line: logLine,
+        file: pendingLocation.file,
+        level: 'error',
+        message: msg,
+        content,
+        raw: content,
+      })
+      pendingLocation = {}
+      continue
+    }
+
     let level: LatexLogEntry['level'] | null = null
     let message: string | null = null
 
-    let m: RegExpMatchArray | null
     if ((m = trimmed.match(LOWER_DIAG_REGEX))) {
       level = m[1] === 'error' ? 'error' : 'warning'
       message = m[2]
     } else if ((m = trimmed.match(UPPER_DIAG_REGEX))) {
+      // `ERROR: In file <filename>` is a preamble for a schema-validation error;
+      // store the filename and defer the entry to the (line N, …) line that follows.
+      const inFile = m[2].trim().match(QUARTO_IN_FILE_REGEX)
+      if (inFile) {
+        pendingLocation = { ...pendingLocation, file: inFile[1].trim() }
+        continue
+      }
       level = m[1] === 'ERROR' ? 'error' : 'warning'
       message = m[2]
     } else if ((m = trimmed.match(PANDOC_REGEX))) {