Keep constant error cells from an opened .xlsx, report them, write them back (#227)

README.en.md

@@ -44,7 +44,7 @@ right here, with the URL, the header and the data never passing through our serv
   <img alt="Tailwind CSS" src="https://img.shields.io/badge/Tailwind_CSS-4-06B6D4?logo=tailwindcss&logoColor=white">
   <img alt="Zustand" src="https://img.shields.io/badge/Zustand-5-443E38">
   <a href="https://excel-to-go.vercel.app"><img alt="Open the app" src="https://img.shields.io/badge/▶_try_it-excel--to--go.vercel.app-2F9E44"></a>
-  <img alt="Vitest" src="https://img.shields.io/badge/tests-1974%20passing-2F9E44?logo=vitest&logoColor=white">
+  <img alt="Vitest" src="https://img.shields.io/badge/tests-1979%20passing-2F9E44?logo=vitest&logoColor=white">
   <img alt="CI" src="https://github.com/SuruchBoss/ExcelToGo/actions/workflows/ci.yml/badge.svg">
 </p>
 
@@ -65,7 +65,7 @@ self-hosted, straight from PostgreSQL/MySQL — one saved read-only query, and n
 and full-fidelity Excel/PDF export, where a chart exported to `.xlsx` is a real, editable chart
 bound to its cells, because the OOXML chart parts are written by hand (ExcelJS writes none). Plus optional
 bring-your-own-backend cloud save and live co-editing over it — presence, last-writer-wins with the loser told, and
-an undo that does not erase the other person's work. Bilingual UI (Thai/English), 1974 automated tests.
+an undo that does not erase the other person's work. Bilingual UI (Thai/English), 1979 automated tests.
 
 ---
 
@@ -109,7 +109,7 @@ Want the harder parts: [embedding a Thai font in the PDF, with stacked tone mark
 
 ---
 
-### 🧪 What 1974 passing tests could not catch
+### 🧪 What 1979 passing tests could not catch
 
 Every test of the assistant **mocks the model** — it returns what I imagined it would. Put a real
 API key behind it, ask fourteen ordinary questions, and **six answers used functions this engine
@@ -120,7 +120,7 @@ Then **the first fix made it worse.** The rule started as "give the closest form
 allows", so _"join all the names into one line"_ came back as `=SUM(A2:A20)` — `0` in the cell, no
 error, nothing to notice. **A visible `#NAME?` traded for an invisible wrong number.**
 
-**And it happened again, in a different place.** With every gate green — 1974 tests, `axe` clean on
+**And it happened again, in a different place.** With every gate green — 1979 tests, `axe` clean on
 both pages at two widths — an hour of clicking through the public build the way a first-time visitor
 would found three things no gate can see:
 
@@ -395,7 +395,7 @@ Other available commands:
 | `npm run build` | Build a production bundle |
 | `npm run start` | Run the production build (run `npm run build` first) |
 | `npm run lint` | Check code quality with ESLint |
-| `npm test` | Run the 1974-case Vitest suite |
+| `npm test` | Run the 1979-case Vitest suite |
 | `npm run check:readme` | Check the READMEs still match the code (links/images/test count/new modules/both languages) |
 | `npm run check:screens` | Figures printed on a screenshot still match the source |
 | `npm run check:rls` | Two real accounts against your own Supabase: does the database refuse what the policies say it should (needs env) |
@@ -2512,12 +2512,16 @@ package again as it opens and **says so before anything is edited**: what, how m
 | Excel PivotTables | values only | static numbers, not a PivotTable |
 | Formulas calling a function the engine lacks | `#NAME?` | **the formula is kept**, and Excel calculates it |
 | Range names that cannot come in (a formula, a whole column, several areas, or a sheet the file lacks) | formulas using them read `#NAME?` | the name is lost; formulas still carry it |
+| Cells holding a constant error value (`#DIV/0!`, `#N/A`) | shown as the text of the code; a formula that reads one does not see an error, so `SUM` steps over it (until [#226](https://github.com/SuruchBoss/ExcelToGo/issues/226)) | **written back as the error value** |
 | External links to other files | values do not update | lost |
 | Macros (VBA) | not run | lost |
 
 <p align="center"><img src="public/screenshots/en/69-file-losses.png" width="820"></p>
 
 - **A plain file sees nothing.** The report comes up only when something is actually lost.
+- **A constant error cell used to open blank, with nothing said** (#227), and a total over it read as a clean number. It now
+  keeps its code and goes back out as the error it was. An error code typed as Excel spells it (`#N/A`, `#DIV/0!`) also
+  goes out as the error, as Excel would store it; a leading apostrophe or the Text format keeps it text.
 - **Got it** closes it. It opens again from the **menu** (or the amber button beside Export Excel from 1366px) for as long
   as the file's sheets are open; undoing the open, or opening another file over it, takes the report away too.
 - It reads the original package, not what the importer returned, because what the importer returned is exactly what
@@ -3010,7 +3014,7 @@ architecture behind it.
 | `@anthropic-ai/sdk` | Connects to the Claude API for the AI assistant |
 | `lucide-react` | UI icons |
 | `clsx` | Conditional className composition |
-| `vitest` | Unit tests for the formula engine, sort logic, JSON-to-table conversion, pagination, rate limiting, templates, file fidelity, conditional formatting and live blocks (1974 cases) |
+| `vitest` | Unit tests for the formula engine, sort logic, JSON-to-table conversion, pagination, rate limiting, templates, file fidelity, conditional formatting and live blocks (1979 cases) |
 
 > **Note:** No off-the-shelf formula library (e.g. HyperFormula) is used — the **formula engine is hand-written**
 > (tokenizer, parser, evaluator, and functions) to keep full control over its behavior. See
@@ -3284,7 +3288,7 @@ src/
     fillSeries.ts            # What dragging the corner continues into — numbers, Thai days and months, quarters, formulas
     sheetSearch.ts           # Find and replace over the raw text rather than the displayed result
     workbookRefs.ts          # The formula rewrites that are not a fact about one sheet: cross-sheet shifts, renames
-    fileLosses.ts            # What an opened file holds that the app can't keep (pictures, charts, PivotTables, macros, links, missing functions), read from the package (#83)
+    fileLosses.ts            # What an opened file holds that the app can't keep (pictures, charts, PivotTables, macros, links, missing functions, constant error values), read from the package (#83)
     sheetNames.ts            # Excel's sheet-name rules in one place: ≤31 chars, no \ / ? * [ ] :, unique ignoring case (#54)
     byok.ts                  # The visitor's own API key: this tab only, masked when shown
     sheet.ts                 # The core sheet data model, whole-sheet computation, applying a formula by scope,
@@ -4050,13 +4054,13 @@ the framework bundle itself, which isn't a trade worth making here. Written down
 ## 🧪 Testing
 
 ```bash
-npm test      # 1974 cases across 140 files, via Vitest
+npm test      # 1979 cases across 140 files, via Vitest
 ```
 
 Testing is focused on the **formula engine, sort logic, JSON-to-table conversion, pagination, rate-limit backoff, Excel templates and live-block placement** — pure functions with no React/DOM dependency, so
 they run fast and give high confidence.
 
-**But not one of those 1974 cases opens the app**, and nearly every bug this project found by hand lived in
+**But not one of those 1979 cases opens the app**, and nearly every bug this project found by hand lived in
 the wiring *between* pieces that all passed their tests — the toolbar's "+ row" called `addRow`, which
 announced nothing, while `insertRowAtSelection` next to it announced correctly (both tested) · the AI
 assistant sent a range including its text header, because the context builder read raw `sheet.cells`
@@ -4175,10 +4179,10 @@ once; disable `ArrowRight` in the grid and two assertions in the third fail. (Th
 second one stayed green: the `case` I inserted landed *after* the existing `case "ArrowRight"` and was dead
 code. Proving a gate means checking that the thing you meant to break actually broke.)
 
-> **1974 tests passed, and 43% of the assistant's answers were unusable** — because those tests mock
+> **1979 tests passed, and 43% of the assistant's answers were unusable** — because those tests mock
 > the model, so it returns what the test author imagined. A test count says what you thought to ask,
 > not whether you asked enough. Only a real API key found this: see
-> [What 1974 passing tests could not catch](#-what-1974-passing-tests-could-not-catch), repeatable
+> [What 1979 passing tests could not catch](#-what-1979-passing-tests-could-not-catch), repeatable
 > with `npm run check:ai`.
 
 | File | Cases | Tests |
@@ -4219,8 +4223,8 @@ code. Proving a gate means checking that the thing you meant to break actually b
 | `sheetNames.test.ts` | 7 | Excel's sheet-name rules (#54): each rule broken, case counted as one name, cleaning a name and finding a free one, + never reusing a name after a delete, an old save's duplicate keeping its formulas on the first tab, an invalid name renamed with its formulas |
 | `sheetMerges.test.ts` | 35 | Which cells a merge swallows, shifting merges on row/column insert and delete, dropping one that collapses to a single cell |
 | `sheetTemplate.test.ts` | 14 | Which cells are locked vs. fields, inline and range-backed dropdown options, column-width conversion |
-| `fileLosses.test.ts` | 10 | What an opened file can't keep (#83): a real file with a picture, a chart and a function the engine lacks, counted with its sheet; that formula exported as it was; a plain file reporting nothing; `_xlfn.` spelling of a function the engine has not counted; PivotTables, shapes, macros, links and a chart sheet as the spec lays them out; a non-zip not failing the open; range names that cannot come in (#60) as one line of the same report, after the missing functions, the whole report for a file with nothing else, and still said when the package cannot be read again |
-| `excelIO.test.ts` | 55 | Builds a real .xlsx and round-trips it: reading fields/dropdowns/widths, an unprotected file isn't a template, export→import comes back identical, and styling (fills/font sizes/borders/row heights/merges) round-trips, as do all five kinds of conditional formatting rule and cell notes (both the plain-string and Excel's rich-text form), cross-sheet dropdowns read from the sheet the rule names (quoted names, a hidden sheet, a missing one, and the PaynEat ERP draft-0 template), a column exactly width 9 still 9 after export (#136), a merge in the file holding its value in the top-left cell only with SUM/COUNTA matching Excel and the merge still exported (#55) |
+| `fileLosses.test.ts` | 12 | What an opened file can't keep (#83): a real file with a picture, a chart and a function the engine lacks, counted with its sheet; that formula exported as it was; a plain file reporting nothing; `_xlfn.` spelling of a function the engine has not counted; PivotTables, shapes, macros, links and a chart sheet as the spec lays them out; a non-zip not failing the open; range names that cannot come in (#60) as one line of the same report, after the missing functions, the whole report for a file with nothing else, and still said when the package cannot be read again; constant error cells (#227) counted with their sheet while a formula whose result is an error is not, and still counted after an export and a reopen |
+| `excelIO.test.ts` | 58 | Builds a real .xlsx and round-trips it: reading fields/dropdowns/widths, an unprotected file isn't a template, export→import comes back identical, and styling (fills/font sizes/borders/row heights/merges) round-trips, as do all five kinds of conditional formatting rule and cell notes (both the plain-string and Excel's rich-text form), cross-sheet dropdowns read from the sheet the rule names (quoted names, a hidden sheet, a missing one, and the PaynEat ERP draft-0 template), a column exactly width 9 still 9 after export (#136), a merge in the file holding its value in the top-left cell only with SUM/COUNTA matching Excel and the merge still exported (#55), a real `t="e"` cell opening as its error code rather than blank, going back out as `t="e"` and still there on a reopen, while `'#N/A` and a Text-formatted cell go out as text (#227) |
 | `charts.test.ts` | 42 | Reading a range into series and labels (including a text label column), gaps for non-numbers, a zero-anchored axis, moving/resizing/clamping a chart's frame, what the legend names per kind, shifting on edits |
 | `server/urlGuard.test.ts` | 31 | Addresses the server refuses to reach (loopback, private ranges, cloud metadata, IPv6 link-local), IPv4 embedded in IPv6 (`::ffff:`, `::`, SIIT, NAT64, 6to4, Teredo), non-http schemes, and the allowlist |
 | `server/sourcesAuth.test.ts` | 9 | No token means off, right/wrong/prefix tokens, and telling "switched off" apart from "wrong token" |