fix(input): stop drafting-aid keys from cancelling the command

F8 reached ORTHO as an ordinary command, and dispatching a command tears
down whatever is running first: the active command dropped, its preview
cleared, its base point forgotten. So pressing F8 partway through a LINE
abandoned the line, and during a MOVE it took the dragged ghost with it.

A function key gets pressed mid-command — that is what it is for.
Toggles that only flip a flag now skip the teardown: ORTHO, GRID, SNAP,
POLAR, and the drafting-settings popup. None of them starts a command,
opens a document or reads geometry, so there is nothing for the teardown
to protect.

F7, F9 and F10 came through the same path and were broken the same way;
they are fixed with F8. F3, F11 and F12 already had messages of their
own and were never affected.

Closes #677

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

src/app/commands/mod.rs

@@ -65,6 +65,16 @@ impl OpenCADStudio {
         // the first space are left untouched. A non-alias passes through as-is.
         let resolved = self.resolve_alias(cmd);
         let cmd = resolved.as_deref().unwrap_or(cmd);
+        // A drafting aid only flips a flag, so it must not disturb whatever is
+        // already running: pressing F8 partway through a LINE means "constrain
+        // the rest of this line", not "abandon it". Everything below tears the
+        // running command down, so a transparent one skips straight past it.
+        // (#677)
+        if is_transparent(cmd) {
+            return self
+                .dispatch_families(cmd, i)
+                .unwrap_or_else(Task::none);
+        }
         // Starting a command closes any open ribbon dropdown (e.g. a style
         // combo left open) so it does not stay stuck behind the new tool.
         self.ribbon.close_dropdown();
@@ -232,6 +242,21 @@ impl OpenCADStudio {
     }
 }
 
+/// Commands that toggle a drafting aid and nothing else.
+///
+/// They are reachable from a function key, and a function key gets pressed
+/// mid-command — that is the point of it. Running them through the ordinary
+/// path cancelled the active command, cleared its preview and dropped its base
+/// point, so F8 during a MOVE both ended the move and made the dragged ghost
+/// vanish. Nothing here starts a command, opens a document or reads geometry,
+/// so there is nothing for the teardown to protect. (#677)
+pub fn is_transparent(cmd: &str) -> bool {
+    matches!(
+        cmd,
+        "ORTHO" | "GRID" | "SNAP" | "POLAR" | "OSNAP" | "DSETTINGS"
+    )
+}
+
 /// Whether `cmd` makes sense on the Start (welcome) tab — document lifecycle,
 /// links, and app-wide configuration; nothing that reads the scene. Single
 /// source of truth: the dispatch gate refuses everything else, and the ribbon