Extract `_copy_close_to_null_rows()` with explicit mutation
bounds, searchable close-copy comments, and preserved activity
fields. Type and document `maybe_fill_null_segments()` including
its distinction from packed timestamp-gap repair.
Disable relative epoch tolerance when validating synthetic
stamps: an overfull reservation must not duplicate the right
boundary. Cover modern epochs, typed empty replies, packed gaps,
and unchanged rejected inputs.
Prompt-IO: ai/prompt-io/codex/20260924T165757Z_1da9b760_prompt_io.md
(this patch was generated in some part by `codex` using
`gpt-6` (`openai`))
Gud Boi