Fix compile error propagation: 'failure' instead of HTTP 500

LocalCommandRunner: attach captured stdout to the error object when
  exit code is 1, so callers can read Quarto's output even on failure.

QuartoRunner: stop propagating plain 'exited' errors from Quarto up
  to CompileManager. A Quarto exit-code-1 is a compile failure, not a
  server error — CLSI already detects failure by the absence of
  output.pdf and returns status='failure' (HTTP 200). Previously it
  fell through to the generic error handler (HTTP 500), which caused
  the frontend to show "Server Error" instead of the log panel.
  Only true process-level errors (terminated, timedout) are propagated.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/clsi/app/js/LocalCommandRunner.js

@@ -89,9 +89,10 @@ export default CommandRunner = {
         err.terminated = true
         return callback(err)
       } else if (code === 1) {
-        // exit status from chktex
+        // exit status from chktex (and any compiler that exits 1 on failure)
         err = new Error('exited')
         err.code = code
+        err.stdout = stdout // preserve captured output for callers
         return callback(err)
       } else {
         return callback(null, { stdout, exitCode: code })

services/clsi/app/js/QuartoRunner.js

@@ -11,7 +11,10 @@ function runQuarto(compileName, options, callback) {
   const { directory, mainFile, image, environment, compileGroup } = options
   const timeout = options.timeout || 60000
 
-  logger.debug({ directory, timeout, mainFile, compileGroup }, 'starting quarto compile')
+  logger.debug(
+    { directory, timeout, mainFile, compileGroup },
+    'starting quarto compile'
+  )
 
   const command = _buildQuartoCommand(mainFile)
 
@@ -26,22 +29,31 @@ function runQuarto(compileName, options, callback) {
     null,
     function (error, output) {
       delete ProcessTable[compileName]
-      if (error) {
-        // Still try to write whatever output we captured before the error
-        _writeLogOutput(compileName, directory, output, () => callback(error))
-        return
+
+      // Propagate real process-level errors (killed, timed out) but NOT
+      // ordinary non-zero exit codes from Quarto itself.  A Quarto compile
+      // failure (exit code 1) is not a server error — the absence of
+      // output.pdf is sufficient for CompileController to return 'failure'.
+      if (error && (error.terminated || error.timedout)) {
+        return callback(error)
       }
-      _writeLogOutput(compileName, directory, output, () => callback(null, output))
+
+      // On exit-code-1 errors LocalCommandRunner attaches stdout to the
+      // error object; merge it so _writeLogOutput can persist it.
+      const combined = output || (error ? { stdout: error.stdout || '' } : null)
+      _writeLogOutput(compileName, directory, combined, () =>
+        callback(null, combined)
+      )
     }
   )
 }
 
 function _buildQuartoCommand(mainFile) {
-  // Run through a POSIX shell so we can merge stderr into stdout.
+  // Run through a POSIX shell so stderr is merged into stdout (2>&1).
   // Quarto writes all progress and error messages to stderr; without this
-  // merge the UI would show nothing in the log panel on failure.
-  // LocalCommandRunner replaces $COMPILE_DIR before the shell sees the string,
-  // so the substitution is safe and no shell variable expansion occurs.
+  // the log panel would be empty on failure.
+  // LocalCommandRunner replaces $COMPILE_DIR before the shell sees the
+  // string, so no shell variable expansion occurs for that token.
   const quartoArgs = [
     'quarto',
     'render',