#92: import XLSB worksheet data and saved formula results

docs/cli.md

@@ -3,6 +3,10 @@
 Headless GridCraft: inspect, convert, evaluate, script and serve MCP without a window. Errors go to stderr with a
 non-zero exit code.
 
+`.xlsb` files support [worksheet data import](xlsb-import.md). Formula cells use their last saved
+values; source formatting and other workbook features are omitted. Import warnings go to stderr.
+Convert to `.xlsx` to save the imported workbook; XLSB output is not supported.
+
 ```sh
 cargo install --path apps/gridcraft-cli     # or: cargo run -p gridcraft-cli -- <subcommand>
 ```

docs/xlsb-import.md

@@ -0,0 +1,22 @@
+# Importing Excel binary workbooks
+
+Open an `.xlsb` file with File → Open, drag it onto GridCraft, or pass it to the CLI.
+GridCraft imports worksheet data into a new workbook and shows the conversion limits.
+
+The import reads worksheet names, visibility, numbers, text, booleans, errors and merged
+cells. Formula cells become their **last saved results**, not live formulas. Those results
+may be out of date if the source application did not recalculate before saving.
+
+Source formatting is omitted: dates, times, percentages and currencies initially display as
+their underlying numbers. The workbook's date system is retained. Charts, images, names,
+macros and other workbook features are not imported. GridCraft does not write XLSB files.
+
+Save opens Save As and suggests a new `.xlsx` file. The source XLSB file is not used as the
+workbook's save destination; requests to save to `.xlsb` return an error.
+
+```sh
+gridcraft-cli info source.xlsb
+gridcraft-cli convert source.xlsb imported.xlsx
+```
+
+CLI import warnings go to stderr, leaving structured output on stdout available for scripts.