fix(command): refuse a malformed coordinate on : and let a later segment see an earlier one (improvise-31oe.3)

PR #316 review blockers. A cursor fallback (clear-cell, yank, paste,
drill-into-cell) now answers only for coordinates that were omitted, so
`:clear-cell Type/Clothing Month/Feb junk` is refused instead of clearing the
cursor's cell. The unknown-name checks move from `execute` to a RequireKnown
effect run at apply time, so `:create-view Second . switch-view Second` is
accepted as `improvise cmd` accepts it. Also pins that a quoted `.` is an
argument.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

context/code/cli.md

@@ -478,9 +478,22 @@ wrote it into `hidden_items`), `toggle-group`, and `switch-view` (the effect
 ignores a view it lacks, and says nothing). `set-page` with an unknown item was
 worse than a no-op: it wrote the name into `page_selections`.
 
-The check is in the **commands**, not the effects, on purpose. The effects are
-also the wire's mutation path (`model_effects`, gotcha 38), and a refusing
-effect there becomes a frame rejection (`MutationRefused`). That is arguably
-right, but it changes the protocol, and a browser composes these only from
-names it was sent. So it is left for a ticket of its own rather than slipped
-in here.
+The check runs at **apply** time, as an effect of its own. `execute` runs
+against one context built before the line ran, and a `:` line builds every
+segment up front, so a check in `execute` refused
+`create-view Second . switch-view Second` and
+`add-item Type Tools . set-page Type Tools` after their first halves had landed,
+while `improvise cmd` (which rebuilds the context per segment) accepted them.
+Each of these commands therefore returns `RequireKnown(needs)` followed by the
+real effect. `RequireKnown` refuses and aborts the batch (gotcha 21), so the
+real effect never applies. It is a `ViewOnly` effect that writes nothing and is
+off the wire on purpose: the wire's own effects (`model_effects`, gotcha 38)
+stay non-refusing, since a refusing effect there becomes a frame rejection
+(`MutationRefused`). That is arguably right, but it changes the protocol, and
+a browser composes these only from names it was sent. It is left for a ticket
+of its own.
+
+The interactive cursor fallbacks of `clear-cell`, `yank`, `paste` and
+`drill-into-cell` answer only for coordinates that were OMITTED
+(`only_when_omitted`). Coordinates that were given and are malformed are
+refused, never replaced by the cursor's cell.