[ShixiangWang]

What

Repairs the scheduled site leg — red since 2026-10-22 (last green 0322d38,
run 39722405686) — and re-arms the selfcheck law that should have caught it.

Root cause, measured twice

Two shapes of one defect, both invisible to the step's own guard:

Run	Job	Shape
42216557267	127887921027	bare closure — R.home read without call parens → cannot coerce type 'closure' to vector of type 'character'
42367209708	128387675594	binless call — file.path(R.home(), "Rscript") names <home>/Rscript, a path that exists on no Linux R install → error in running command / Execution halted

PR #80 (5396971 fix(ci): call R.home() in the scheduled site legs) moved the
failure from the first shape to the second; it did not fix the leg. Both shapes
leave attr(res, "status") NULL when the spawn never happens, so the leg's own
if (!is.null(st) && st != 0L) stop(...) guard cannot fire. This must be a
source law, not a runtime probe.

Fix

• Both spawn sites (site bundle, deploy guard) now use
  file.path(R.home("bin"), "Rscript"), the spelling already in use at
  ci.yml:705.
• tools/ci-selfcheck.py gains binless_rhome_hits plus a gating check, and
  the pre-existing bare_rhome_hits discriminator is corrected from != "()"
  to != "(" so the argument-bearing call is no longer mis-flagged as a bare
  closure.
• Firing controls widened in the same change: both measured typo shapes must
  redden, and R.home(), R.home("bin"), and file.path(R.home("bin"), "R")
  must pass.
• use-cache: true dropped from the CRAN-shape monolith's
  setup-r-dependencies step. The pinned v2 action declares cache (required,
  default 'true') and has no use-cache input, so the line was silently
  ignored while caching was already on — a behaviour-neutral removal.

Evidence

• Positive control: binless_rhome_hits returns 2 hits on main, 0 on this
  tree.
• python3 tools/ci-selfcheck.py → exit 0, zero FAIL lines, all four R.home
  checks PASS.
• tests/testthat/test-cjk-census.R → 23 pass, 0 fail (it covers both edited
  files, and no new non-ASCII was introduced).

Test plan

• guards job green — python3 tools/ci-selfcheck.py is a named PR-gate
  step (ci.yml:145), so the new law gates this PR itself.
• After merge: re-dispatch .github/workflows/scheduled.yml and convert the
  site job from red to measured green.