collectPageEmbedsFromPmJson (and the sibling collectors/remap) recursed with no
guard, so a pathological/cyclic non-JSON input could stack-overflow (RangeError).
Add a depth cap (1000, far above any real doc nesting) so such input is handled
gracefully. Normal documents are unaffected. Updates a stale test that asserted
the old throwing behavior.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>