Surface missing-Python-package errors clearly in the Quarto log

When a {python} cell fails with ModuleNotFoundError/ImportError, the Quarto
log parser now emits an actionable error ('Python package "X" is not
installed on the server') noting which scientific packages are pre-installed,
instead of leaking an opaque traceback line.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/web/frontend/js/ide/log-parser/quarto-log-parser.ts

@@ -32,6 +32,11 @@ const UPPER_DIAG_REGEX = /^(ERROR|WARNING): (.*)$/
 const PANDOC_REGEX = /^\[(WARNING|ERROR|INFO)\] (.*)$/
 // knitr/R: `Quitting from lines 3-7 (slides.qmd)`
 const R_QUITTING_REGEX = /^Quitting from lines? (\d+)(?:-\d+)?\s*(?:\(([^)]+)\))?/
+// Python (Jupyter cell execution): a missing dependency, e.g.
+//   ModuleNotFoundError: No module named 'pandas'
+//   ImportError: No module named scipy
+const PY_MODULE_REGEX =
+  /^(?:ModuleNotFoundError|ImportError): No module named ['"]?([\w.]+)['"]?/
 // A typst diagnostic location line: `  ┌─ main.typ:5:10` / `  --> main.typ:5:10`
 const TYPST_LOCATION_REGEX = /(?:[┌╭]─|-->)\s*(.+?):(\d+):(\d+)/
 
@@ -67,6 +72,28 @@ export default function parseQuartoLog(rawLog: string): ParseResult {
       continue
     }
 
+    // A missing Python package when executing a {python} cell. Turn the raw
+    // traceback line into an actionable message rather than letting it slip
+    // through as an opaque error (or not be surfaced at all).
+    const pyModule = trimmed.match(PY_MODULE_REGEX)
+    if (pyModule) {
+      const pkg = pyModule[1]
+      data.push({
+        line: pendingLocation.line ?? null,
+        file: pendingLocation.file,
+        level: 'error',
+        message: `Python package "${pkg}" is not installed on the server`,
+        content:
+          `${clean}\n\nThe Python package "${pkg}" is not available in the ` +
+          `compile environment. Common scientific packages (numpy, pandas, ` +
+          `scipy, matplotlib, seaborn, scikit-learn, sympy, plotly) are ` +
+          `pre-installed; others must be added to the server image.`,
+        raw: clean,
+      })
+      pendingLocation = {}
+      continue
+    }
+
     let level: LatexLogEntry['level'] | null = null
     let message: string | null = null