fix: handle long/multiline prompts in _resolve_prompt

Skip the file-existence check when the prompt contains newlines (can't
be a filename) and catch OSError for prompts that exceed the OS path
length limit.

bulkgen/builder.py

@@ -57,9 +57,14 @@ class BuildResult:
 
 def _resolve_prompt(prompt_value: str, project_dir: Path) -> str:
     """Resolve a prompt: read from file if the path exists, otherwise use as-is."""
-    candidate = project_dir / prompt_value
-    if candidate.is_file():
-        return candidate.read_text()
+    if "\n" in prompt_value:
+        return prompt_value
+    try:
+        candidate = project_dir / prompt_value
+        if candidate.is_file():
+            return candidate.read_text()
+    except OSError:
+        pass
     return prompt_value