feat(f34): Excel workbook interoperability

CHANGELOG.md

@@ -42,6 +42,30 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   are written as NULL and counted into a per-column warning report; columns
   without a schema export as text verbatim. A columnar document opens
   unsaved so a later Save can never overwrite the binary source with CSV.
+- **Excel `.xlsx` interoperability** (F34): read and produce Excel workbooks
+  without a detour through CSV, and without a formula engine. The open chooser
+  inspects a workbook up front — every sheet with its visibility (including
+  hidden and very-hidden sheets), named tables and named ranges, per-sheet used
+  ranges and dimensions, formula and merged-cell counts, detected header-row
+  candidates and a bounded preview. Import a chosen sheet, named table or named
+  range (optionally a specific `A1` cell range), with control over the header
+  row (first row, a chosen row, or none), merged cells (keep the top-left value
+  only, or repeat it across the region), formulas (cached result, formula text,
+  or blank — with a warning when a workbook has formulas but no cached results,
+  since CEESVEE never evaluates them) and blank-row/blank-column trimming.
+  Imports honour the workbook's 1900/1904 date system so dates never shift and
+  the Excel 1900 leap-year quirk is preserved, and leading-zero text (ZIP and
+  account codes) stays text — cell types are respected, never numeric-coerced.
+  Every import produces a fresh CEESVEE document (there is no in-place `.xlsx`
+  save); the original workbook is never modified. Export one sheet from one
+  document, or several sheets (one per open tab) into a single workbook, with
+  optional bold/filled header styling, a frozen header row, an autofilter, and
+  column widths from the grid or autofit. Typed columns (from the F31 schema)
+  export as real Excel numbers, booleans and dates; text stays text and cells
+  invalid under their schema fall back to text. Excel's 1,048,576-row ×
+  16,384-column limits are checked before writing (an over-limit export is
+  refused up front), and the workbook is committed through the atomic-save
+  pipeline, so a failed or cancelled export never touches an existing file.
 - **Row bookmarks, tags & notes** (F40): mark and annotate records without
   touching the source data. Star or flag a row, apply multiple named tags
   (a per-document tag namespace with usage counts), and attach a row note or

README.md

@@ -58,6 +58,17 @@ and faithful on large, real-world delimited files.**
   explode into rows, or drop). Signed/unsigned 64-bit integers, exact
   decimal precision/scale, timestamps with timezone, and null-vs-empty-string
   all survive intact.
+- **Open Excel `.xlsx`** — a chooser lists every sheet (including hidden and
+  very-hidden ones), named tables and ranges, used ranges and dimensions, and
+  formula/merged-cell counts. Pick a sheet, table or cell range; choose the
+  header row (first, a chosen row, or none), how merged cells are handled
+  (top-left value only, or repeated across the region) and how formulas are
+  handled (cached result, formula text, or blank — with a warning when a
+  workbook has formulas but no cached results), and blank-row/column trimming.
+  The workbook's 1900/1904 date system is honoured (no date shifting, the
+  1900 leap-year quirk preserved) and leading-zero text stays text. Every
+  import creates a new document — there is no in-place `.xlsx` save, so the
+  original workbook is never modified.
 - Auto-detect the **delimiter** (comma, tab, semicolon, pipe) with a manual /
   custom override — plus an **advanced import** for preambles, comment
   lines, custom quoting/escaping, multi-row headers, and footers.
@@ -121,6 +132,14 @@ and faithful on large, real-world delimited files.**
   column's declared logical type to the matching arrow type (preserving 64-bit
   integer widths, decimal precision/scale, and timestamp timezones); cells
   that can't be represented are written as NULL and reported per column.
+- **Export to Excel `.xlsx`** — write one document — or several open tabs as
+  one sheet each — to a single workbook, with optional bold/filled header
+  styling, a frozen header row, an autofilter, and column widths from the grid
+  or autofit. Typed columns emit real Excel numbers, booleans, and dates from
+  the declared schema (text stays text; cells invalid under their schema fall
+  back to text). Excel's 1,048,576-row × 16,384-column limits are checked
+  before anything is written, and the workbook commits through the same atomic
+  save pipeline, so a failed or cancelled export never touches an existing file.
 
 **Reliability**
 

src-tauri/Cargo.toml

@@ -55,6 +55,12 @@ zip = { version = "2", default-features = false, features = ["deflate"] }
 # Parquet & Arrow interop (F32): typed columnar open/export.
 arrow = { version = "59", default-features = false, features = ["ipc"] }
 parquet = { version = "59", default-features = false, features = ["arrow", "snap", "zstd"] }
+# Excel .xlsx interoperability (F34): calamine reads workbooks (the `dates`
+# feature pulls in chrono so date cells honour the workbook epoch), and
+# rust_xlsxwriter produces them (typed values via its native ExcelDateTime, so
+# no extra chrono feature is needed on the writer).
+calamine = { version = "0.36", features = ["dates"] }
+rust_xlsxwriter = "0.96"
 
 # Single-instance is desktop-only: it forwards a second "Open with" launch
 # (and its file argument) to the already-running window instead of spawning a