Codex stop-time review caught that the Phase 2 domain filter
corrupted output when two adjacent kept blocks abutted: the regex's
trailing `\s*` consumed every character of whitespace BEFORE the next
match's leading `\s*`, so block N's body ended on its closing ``` and
block N+1's body started on its `### heading` with no separator at
all. Output: ` ```### Audit / activity feed` on a single line — fence
left unclosed, heading swallowed.
Replace the greedy `\s*` on both sides of each marker with a literal
`\n`, so the regex only consumes the single newline immediately
adjoining the comment. Surrounding blank lines stay in the
surrounding text where they belong, separating adjacent kept blocks
naturally.
Adds a regression guard test that searches the output for ` ```###`
(closing fence directly followed by a level-3 heading on the same
line). Codex effectively asked for it.
3767 vitest pass, format clean. Side effect: dropped blocks now
leave their surrounding blank lines intact, so dropped-block savings
shrink by ~3-5 chars per block; total Phase 2 savings stay within
the 500-char floor the existing test asserts.
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