Variables: Import Data Sets… reads tab-separated files and files without a name column

dataset.import read only commas between cells and refused a file whose
first header cell wasn't `name`. A value that didn't match its
variable's kind, and a repeated data set name, were reported with the
row's record number, which is not the file line after a blank line or a
quoted line break. A data set name over 255 characters gave no line.

- When the header row, read with tabs between cells, has a tab and no
  comma outside quotes, tabs separate the cells. A quoted cell may then
  hold tabs and commas.
- Without a `name` column every header cell is a variable, and the rows
  take the first free names Data Set 1, Data Set 2 and so on, as Capture
  Data Set and blank name cells do. A first header cell `name`, in any
  case, still holds the data set names.
- Value errors, a repeated data set name and a name over 255 characters
  give the file line the row starts on.
- The Variables panel's Import Data Sets… dialog also lists .tsv files.
- import_fuzz.rs imports random text, random bytes and mutated exports,
  comma- and tab-separated, into a document with bound text, visibility
  and graph variables, selects up to three of the imported data sets in
  turn, and exports every data set.

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

docs/mcp.md

@@ -1083,7 +1083,10 @@ already walks Image Trace. Short agent entry points:
 - Data sets: `dataset.list`, `dataset.new {name, values?}`, `dataset.set {name, values?}`, `dataset.rename`,
   `dataset.delete`, `dataset.capture`, `dataset.update`, `dataset.select {name}`, `dataset.next` /
   `dataset.prev` (each `dataset.select` / next / prev is one undo step over every bound object), `dataset.import {path|data|dataBase64|csv}` /
-  `dataset.export {path?}` (CSV: `name`, then one column per variable).
+  `dataset.export {path?}` (CSV: `name`, then one column per variable). `dataset.import` also reads tab-separated
+  files, and files whose first header cell isn't `name`: every header cell is then a variable, and the rows take the
+  first free names `Data Set 1`, `Data Set 2` and so on. An import error about a row's values or name gives the file
+  line the row starts on.
 - Batch: `action.batch {commands, source?: folder|datasets, folder?, destination?: none|saveAndClose|folder,
   destinationFolder?, overrideOpen?, overrideSave?, overrideExport?, includeSubdirs?, stopOnError?}` plays an
   action on every file in a folder or every data set (the Actions panel menu's Batch…).

docs/target-app-parity.md

@@ -415,6 +415,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - Variables: `dataset.select`, `dataset.next` and `dataset.prev` name the area type and type on a path whose text they rewrote and that doesn't fit, in the reply's `overflow` key, as `text.setText` does.
   - Actions panel (record/playback, persisted), generic parameter dialogs for every "…" command.
   - Variables (data merge): text, visibility and image variables bound to objects (an object may carry several), dataset rows applied in one undo step (`variable.*`, `dataset.*`) from a Variables panel and Window › Variables, with dialogs to define, bind and edit, Make Text/Visibility/Image Dynamic, Capture/Update Data Set, CSV import/export (`dataset.import` / `dataset.export`), and a row in italics when an edit leaves the art not matching it; an image dataset value is a file path and apply keeps the object's bounds; bindings let go of deleted art and locked art is left alone; every command, like the rest, is drivable over MCP and the CLI.
+  - Variables: Import Data Sets… (`dataset.import`) reads tab-separated files as well as comma-separated ones, and files without a `name` column, whose rows take the first free names Data Set 1, Data Set 2 and so on. An import error about a row's values or name gives the file line the row starts on.
   - JSON-lines control channel with real egui pointer and keyboard injection.
   - Synthetic input validates complete gestures before queue mutation: at most 256 drag steps, 16 clicks and 1,024 pending events; up to 64 control requests per frame, with later requests retained for the next frame (#1709).
   - The control server writes each reply through a 64 KiB buffer. On Windows 11 it sends the 17 MB `document.inspect` reply of a document with 50,000 objects on one layer to a client over loopback in 0.09 s instead of 34 s.