- .csv: cells leading with =/+/-/@ (leading whitespace stripped first) are the
CSV-injection/DDE vector the guard cannot recognize, so the front-end refuses
them; the raw cell text is still materialized so a prompt-injection phrase in a
cell is caught by the stage-2 scan (T1). Detach-proof: plain-cell version of
the same file ADMITs. Numeric -/+ leads are the accepted FP (honest-limits).
- folder: walked member-by-member with relative paths preserved, so a reserved
basename member (index.md) lands on the guard's T4 gate; symlinks refused.
Refactor: per-file dispatch shared by top-level drops and folder walk (strict
raises on unsupported top-level suffix, folder skips). Tests 293 -> 300.