Fix LaTeX projects failing to compile (HTTP 500, no logs)

Project.compiler defaults to settings.defaultLatexCompiler ('quarto' in this
fork), so every .tex project carried compiler='quarto'. Since the CLSI runner
is chosen by file extension, a .tex root still goes to LatexRunner, whose
_buildLatexCommand threw `unknown compiler: quarto` — surfacing as an opaque
HTTP 500 with no compile log.

- LatexRunner: fall back to pdfLaTeX when the compiler isn't a known TeX engine
  instead of throwing. Universal safety net (covers existing projects, uploads
  and GitHub imports already saved with compiler='quarto').
- ProjectCreationHandler: store a sensible compiler per flavour at creation via
  a shared _flavourConfig helper — blank/example LaTeX → 'pdflatex',
  Typst → 'typst', Quarto → 'quarto' — so the compiler dropdown reflects the
  engine and LatexRunner receives a valid one directly.

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

services/clsi/app/js/LatexRunner.js

@@ -197,13 +197,13 @@ function _buildLatexCommand(mainFile, opts = {}) {
     command.push(...opts.flags)
   }
 
-  // TeX Engine selection
-  const compilerFlag = COMPILER_FLAGS[opts.compiler]
-  if (compilerFlag) {
-    command.push(compilerFlag)
-  } else {
-    throw new Error(`unknown compiler: ${opts.compiler}`)
-  }
+  // TeX Engine selection. A .tex project may carry a non-LaTeX compiler value
+  // (e.g. 'quarto', the fork-wide default for Project.compiler) because the
+  // runner is chosen by file extension, not by this setting. In that case fall
+  // back to pdfLaTeX rather than throwing — throwing here surfaces as an opaque
+  // HTTP 500 with no compile log.
+  const compilerFlag = COMPILER_FLAGS[opts.compiler] || COMPILER_FLAGS.pdflatex
+  command.push(compilerFlag)
 
   // We want to run latexmk on the tex file which we will automatically
   // generate from the Rtex/Rmd/md file.

services/web/app/src/Features/Project/ProjectCreationHandler.mjs

@@ -85,26 +85,38 @@ async function createProjectFromSnippet(ownerId, projectName, docLines) {
   return project
 }
 
-async function createBasicProject(ownerId, projectName, flavour = 'quarto') {
-  const project = await _createBlankProject(ownerId, projectName)
-
-  // Verso compiles .qmd with Quarto, .tex with latexmk and .typ with Typst;
-  // the root file's extension selects the runner (see CompileManager in CLSI),
-  // so a blank project's flavour is just a choice of template + root name.
-  let templateName, rootDocName
+// Per-flavour blank-project template, root document name and stored compiler.
+function _flavourConfig(flavour) {
   switch (flavour) {
     case 'latex':
-      templateName = 'mainbasic.tex'
-      rootDocName = 'main.tex'
-      break
+      return {
+        templateName: 'mainbasic.tex',
+        rootDocName: 'main.tex',
+        compiler: 'pdflatex',
+      }
     case 'typst':
-      templateName = 'mainbasic.typ'
-      rootDocName = 'main.typ'
-      break
+      return {
+        templateName: 'mainbasic.typ',
+        rootDocName: 'main.typ',
+        compiler: 'typst',
+      }
     default:
-      templateName = 'mainbasic.qmd'
-      rootDocName = 'main.qmd'
+      return {
+        templateName: 'mainbasic.qmd',
+        rootDocName: 'main.qmd',
+        compiler: 'quarto',
+      }
   }
+}
+
+async function createBasicProject(ownerId, projectName, flavour = 'quarto') {
+  // Verso compiles .qmd with Quarto, .tex with latexmk and .typ with Typst;
+  // the root file's extension selects the runner (see CompileManager in CLSI).
+  // Each flavour is a choice of template + root name + the compiler stored on
+  // the project (so the compiler dropdown reflects the engine and LatexRunner
+  // never receives a non-LaTeX compiler for a .tex project).
+  const { templateName, rootDocName, compiler } = _flavourConfig(flavour)
+  const project = await _createBlankProject(ownerId, projectName, { compiler })
 
   const docLines = await _buildTemplate(templateName, ownerId, projectName)
   await _createRootDoc(project, ownerId, docLines, rootDocName)
@@ -187,7 +199,11 @@ async function createExampleProject(
   attributes = {},
   flavour = 'latex'
 ) {
-  const project = await _createBlankProject(ownerId, projectName, attributes)
+  const { compiler } = _flavourConfig(flavour)
+  const project = await _createBlankProject(ownerId, projectName, {
+    ...attributes,
+    compiler,
+  })
 
   let result
   switch (flavour) {