The two catch blocks in importPage() threw an opaque "Error processing file
content" / "Failed to create imported page" BadRequest, hiding the real cause
from the HTTP response. This made a production 400 regression impossible to
diagnose without server log access, and violated the project convention that
errors must never be swallowed.
Extract `${err.name}: ${err.message}` into both the log (full err object kept
for the stack) and the thrown BadRequestException. Inner processMarkdown/
processHTML rethrowing catches and the EE processDocx/processPdf license
catches are left unchanged.
Local reproduction of the happy-dom 14->20 theory failed (full import chain
+ 22 edge cases pass on happy-dom@20.8.9), so the root cause is still pending
the now-visible reason from a recurring 400. Diagnostic script test-import.tsx
added; backlog doc updated with findings.
