R-289: test the cast reader on strings, and fix the spelling that found

Both earlier cast defects were shown by editing CLEAN_GROUND.md in the shared tree,
which is how this session came within a git checkout of c0's uncommitted work and
is also the weaker test. Seven cases now live in check-behaviour as strings.

Writing them found a live one: "<!-- cast : ... -->", one space before the colon,
matched nothing -- not an empty declaration R-288 would refuse but no declaration
at all, so check-rollable widened to the whole duty roster and printed its usual OK
line. check-cited's three spellings again. The reader now takes cast\s*:.

castLikeIn adds the asymmetric half: anything comment-shaped containing cast\w* the
reader did not consume is named by check-rollable, so a spelling nobody anticipated
fails the build instead of silently declaring nobody. Looser than the reader on
purpose -- a false alarm costs a reword, the opposite error costs a guard that
checks the wrong six people and says OK.

Tests then mutation-checked for being load-bearing, each mutation asserted to have
applied after a first pass where three silently did not.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/REVIEW_LOG.md

@@ -6765,3 +6765,42 @@ strength of an agent the scenario does not cast.
 
 Replacing CLEAN GROUND's declaration with `<!-- cast: -->` passes before this change and
 fails after it, naming the line. A scenario with no marker still falls back, unchanged.
+
+## R-289 — the cast reader, tested on strings, and the spelling that testing found
+
+c0's point after R-286: both cast defects were demonstrated by editing CLEAN_GROUND.md in the
+shared tree to watch what the reader did with it. That is how one session came within a
+`git checkout` of another's uncommitted work — and it is also the weaker test. It holds one
+shape at a time, it leaves nothing behind, and it cannot be run again next month.
+
+Seven cases now live in `check-behaviour`, as strings: the real document's shape; the mention
+moved above the declaration (the R-286 bug, which must still read the six); two real
+declarations both seen, with line numbers surviving the code-blanking; a fenced declaration
+ignored; present-and-empty told apart from absent (R-288); spelling; and the odd-marker
+counter.
+
+**Writing them found a live one.** `<!-- cast : ... -->` — one space before the colon —
+matched nothing. Not an empty declaration that R-288 would refuse: *no declaration at all*, so
+check-rollable fell back to the whole duty roster and printed its usual OK line having checked
+every skill in the document against people the scenario does not cast. This is check-cited's
+defect exactly, where `Cite:`, `CITE:` and `cite :` all failed open while the guard reported a
+count identical to a clean tree. The reader now takes `cast\s*:`, case-insensitively.
+
+**And the asymmetric half, because widening only fixes the spellings we thought of.**
+`castLikeIn` recognises anything comment-shaped containing `cast\w*` that the strict reader did
+not consume, and check-rollable names it: `cast =`, `casting:`, `the cast is` all fail the
+build rather than silently declaring nobody. It is deliberately looser than the reader — an
+ordinary comment near the casting section can trip it, and the message says prose belongs in
+backticks, where nothing here looks at it. A false alarm costs a reword; the opposite error
+costs a guard that checks the wrong six people and says OK.
+
+**The tests were then checked for being load-bearing**, by mutating the reader in a worktree
+and reading which of them went red — each mutation asserted to have applied, after a first
+pass where three silently did not and the green that followed proved nothing:
+
+| mutation | red |
+|---|---|
+| `cast\s*:` back to `cast:` | spacing |
+| code-span blanking removed | four, including both R-286 cases |
+| marker list truncated to the first hit | two declarations both seen |
+| odd-marker counter disabled | cast-shaped marker named |