MCP: an integer given as a string or a fraction is refused as the wrong type, not reported as missing

A command that needs a whole number of 0 or more, such as `index` of
`appearance.setItem`, `anchor` of `path.removeAnchor` and
`addon.pen.removePoint`, `sourceDocument` of `edit.dropSelection`, `index`
of `document.activate` and `to` of `document.move`, answered "missing
integer `index`" (or "missing index") both when the key was left out and
when it was given as a value that is not a whole number of 0 or more, such
as "3", 2.5, -1 or true. A value that is given but is not one is now
refused with "`index` must be a whole number", the message object ids
already use. A key left out or given as null is still missing, and an
optional index such as `subpath` keeps its default. Neither error changes
the document or records an undo step.

Docs: docs/mcp.md, docs/target-app-parity.md.

docs/mcp.md

@@ -564,7 +564,13 @@ key, and report a key left out or null as missing. The optional `group` of `live
 (`x` of `shape.rectangle`, `pos` of `guide.add`, `index`, `x` and `y` of the `object.mesh.*` and
 `object.envelope.setMeshPoint` point commands, and the others like them) refuses a value that is not a number with
 `` `x` must be a number, not "40" ``, naming the key and showing the value as given, and reports a key left out or null
-as `` missing number `x` ``; it changes nothing either way. A command that leaves out an object selected inside a
+as `` missing number `x` ``; it changes nothing either way. A command that needs a whole number of 0 or more (`index`
+of `appearance.setItem`, `anchor` of `path.removeAnchor` and `addon.pen.removePoint`, `sourceDocument` of
+`edit.dropSelection`, `index` of `document.activate`, `to` of `document.move`, and the others like them) refuses a
+value such as `"3"`, `2.5`, `-1` or `true` with `` `index` must be a whole number ``, naming the key, and reports a key
+left out or null as missing (such as `` missing integer `index` ``). An optional one, such as `subpath`, keeps its default when
+left out or null; `appearance.setActiveItem` reads a null `index` as clearing the active item.
+A command that leaves out an object selected inside a
 selected group also leaves it out when `ids` list it together with a group that holds it. Every command that takes
 `ids` (or `slices`, for the slice commands) refuses a list with an entry that is not a non-negative integer, or a value
 that is not a list, and changes nothing; it does not act on the other entries. The error for an entry names the key,
@@ -5111,7 +5117,7 @@ path by its control points when one of them has an x or y that is infinite or la
 the canvas (coordinates out of range)".
 `path.curvatureEdit`, `path.removeAnchor`, `path.convertAnchor`, `path.reshapeSegment`, `path.split`,
 `path.setHandle`, `path.moveAnchor` and `path.insertAnchor` edit subpath 0 when `subpath` is absent or null, and refuse a `subpath` that
-is not a whole number of 0 or more, such as 1.5, -1 or "1" ("missing integer `subpath`"); `path.split` refuses such
+is not a whole number of 0 or more, such as 1.5, -1 or "1" ("`subpath` must be a whole number"); `path.split` refuses such
 an `anchor` or `segment` in the same way. The document does not change and no undo step is recorded.
 `path.moveAnchor` to the point the anchor is at, and `path.setHandle` to the point the handle is at on an anchor that
 keeps its kind, leave the document as it is and record no undo step.

docs/target-app-parity.md

@@ -1086,7 +1086,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
     A path segment with a control point whose x or y is infinite or larger in size than `f64::MAX / 16` is measured by its control points, so its bounds hold the whole curve and the canvas check refuses an edit that leaves such a path selected (`path.create` included).
     With Direct Selection, the Pen and the anchor tools, a group, compound path or clip group selected whole shows the anchors of its paths filled, as a path selected whole does; the direction handles still show only on a path that is selected itself. Public references: [Adjust anchor point, handle, and bounding box display size](https://web.archive.org/web/20251114182206/https://helpx.adobe.com/illustrator/desktop/draw-shapes-and-paths/learn-drawing-basics/adjust-anchor-point-handle-and-bounding-box-display-size.html) and [Drawing basics](https://web.archive.org/web/20231130064834/https://helpx.adobe.com/illustrator/using/drawing-basics.html) (archived copies).
     When the Add Anchor Point tool, the Pen's Auto Add, the Smart Pen's Alt-click on a segment or Alt-click with the Scissors adds an anchor to a path with direct-selected anchors or segments (`path.insertAnchor`), the same points stay selected: the anchors and segments after the new anchor are numbered one higher, and a selected segment that the new anchor splits stays selected as its two halves.
-    `path.curvatureEdit`, `path.removeAnchor`, `path.convertAnchor`, `path.reshapeSegment`, `path.split`, `path.setHandle`, `path.moveAnchor` and `path.insertAnchor` refuse a `subpath` that is not a whole number of 0 or more, and `path.split` refuses such an `anchor` or `segment`; without a `subpath` they edit subpath 0.
+    `path.curvatureEdit`, `path.removeAnchor`, `path.convertAnchor`, `path.reshapeSegment`, `path.split`, `path.setHandle`, `path.moveAnchor` and `path.insertAnchor` refuse a `subpath` that is not a whole number of 0 or more, and `path.split` refuses such an `anchor` or `segment`; without a `subpath` they edit subpath 0. A value given that is not a whole number, such as `"1"` or `1.5`, is refused with `` `subpath` must be a whole number ``, naming its key, as are a required index of the Appearance panel and Smart Pen commands, `sourceDocument` of `edit.dropSelection` and `index` and `to` of `document.activate` and `document.move`; a required one left out or null is reported as missing (`tests::params::a_malformed_required_integer_is_not_reported_as_missing`).
     `path.reshapeSegment` refuses a delta of 1e9 pt or longer, as `object.blend.spine.reshapeSegment` does, and `path.convertAnchor` and `path.freehand` refuse a point whose x or y is 1e9 pt or more in size.
     `path.reshapeSegment`, `object.blend.spine.reshapeSegment`, `path.convertAnchor`, `path.curvatureEdit`, `path.insertAnchor`, `path.moveAnchors`, `path.reshape`, `path.close` and the Pencil, Curvature, Knife, Eraser, Path Eraser, Smooth, Join and Blob Brush commands refuse a number, point or handle given as text, such as "10", and leave the document unchanged; `path.convertAnchor` refuses an `x` without a `y`, or a `y` without an `x`.
     `path.close` and `path.setHandle` (`independent`), `path.moveAnchors` (`patterns`), the Pencil (`closed`, `keepSelected`, `fill`), Curvature (`closed` and a point's `corner`), `path.curvatureEdit` (`corner`), `path.reshapeSegment` (`perpendicular`) and the Blob Brush (`keepSelected`, `mergeOnlySelection`, `merge`) refuse a value other than true, false or null, such as "true", and leave the document unchanged.