fix: pre-landing review fixes (pass 2)

An unclosed receipt fence makes the body from that line on one section
the merge never matches, so posted leading prose cannot replace it and a
closed receipt before it stays a receipt; the by-tree pregate mirror must
hold the tests stage (what --stage tests --remote writes) rather than
every check; empty sha/tree strings in a train note are not evidence;
(v1.2.3-rc1 #301) is a version word, not a repository.

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

docs/pregate.md

@@ -284,9 +284,10 @@ printing `PREGATE: … (from the state root's pregate/by-tree/<tree12>.json,
 recorded by another checkout)`. This is for the lane whose `gstack-pregate
 --remote` had to run from a separate clone (a worktree cannot host it): the
 clone's record clears the lane's own checkout as long as both hold the same
-tree. Only a complete run stands in: the mirror must name every registered
-check (so a `--only` or single-stage run is "a partial run without …"), be
-recorded against `origin/<base>` and not under `--policy-from head`;
+tree. Only a run that holds the tests stage stands in (what `--stage tests
+--remote` writes, `checks=[lanes]`; a `--only timing` or preflight-only run
+is "a run without the tests stage"), and it must be recorded against
+`origin/<base>` and not under `--policy-from head`;
 otherwise the `PREGATE:` line says why the mirror cannot stand in. A record
 whose own checks failed or stayed incomplete is final and no mirror overrides
 it. An explicit `--pregate <file>` that verifies is used as before; a mirror