kb: a pipe discards the exit code you meant to read

Fourth occurrence in one campaign, and this one was in a tool I wrote TO BE
the reliable answer. scripts/pr-reviews --wait correctly exited 1 on a
timeout, and my invocation ended in '| tail -20; echo', so the harness
reported 0 — a review window that had EXPIRED read as a review that had
ARRIVED, which is the dangerous direction.

The earlier three: pr-watch reading tr's status through a pipe; a probe
reporting EXIT=0 from a checker that had exited 1; and PIPESTATUS in zsh,
where the array is lowercase pipestatus — the two shells differ, which is its
own trap.

The script's usage now says not to pipe it.

Closes improvise-711n (,.2f yielded zero decimals — the spelling our own docs
show) and improvise-x1ns (the preflight undercount ChatGPT Codex found on a
PR I had already merged unread).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FC2jVn8Au7E9JPkw6bwXXH

scripts/pr-reviews

@@ -16,6 +16,10 @@ exit 0  a review against the current head exists (or --wait was 0)
 exit 1  --wait elapsed with no review against the current head
 exit 4  usage or environment error
 
+DO NOT PIPE THIS INTO head/tail. `$?` is then the pager's status, not this
+script's, and a --wait that timed out reads as success. That trap has cost
+this repo four separate diagnoses. Redirect to a file and read it instead.
+
 A review may target an EARLIER head, which is why the head is compared rather
 than the count: a finding against an old commit may be fixed or still live, and
 only reading it tells you which.