PROPOSED. Framing only; no runtime code.
Buffer::undo gates on ensure_writable() and never consults the intercept
chain, so the add_intercept "read-only" idiom leaves the rope writable
and the owner's own bypass_intercept paint on the undo stack. Four writer
mechanisms across five buffer families are affected; every one was
reproduced by execution at ad41cf1, not inferred.
The document carries the measured reproductions, the full classified
census with its arithmetic shown, the primitive decision with numbered
alternatives, per-criterion bite obligations, and the staging proposal.
Recommended primitive: Buffer::apply_generated_edit(op), exposed as a
{ generated = true } option on the existing Lua mutators, with
set_generated_contents reimplemented as its whole-buffer wrapper. It is
the only candidate in which the buffer is never observably unlocked.
