Progress docs: target-app parity, gaps, alpha gate, readiness by audience (#189)

Progress docs per craftrules standards/progress-docs.md: target-app parity, gaps, roadmap with alpha gate, readiness by audience (full / mainstream / essentials) with Opus 5.5 hours, and feature, format, hardware, UI and localization parity docs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/function-parity.md

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+# Function parity: worksheet functions and formulas
+
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-10 · **Change:** major (created; measured against Microsoft's published Excel function list) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+
+Excel's worksheet functions, category by category, against GridCraft's function library. Part of
+[target-app-parity.md](target-app-parity.md); gaps feed [gaps.md](gaps.md).
+
+## How this is measured
+
+- **Excel's list (523):** Microsoft's "Excel functions (alphabetical)" support page, fetched and
+  parsed on 2026-10-10 (506 rows with their category and the Excel version that introduced
+  them), plus 14 text functions the page lists under combined entries (FIND/FINDB, LEFT/LEFTB,
+  LEN/LENB, MID/MIDB, REPLACE/REPLACEB, RIGHT/RIGHTB, SEARCH/SEARCHB), BETA.INV, and COPILOT and
+  PY (Microsoft 365 functions not on that page when fetched).
+- **Ours (501):** every function spec in `crates/functions/src/*.rs` (`f!("NAME", …)`) plus the
+  evaluator's special forms in `crates/calc/src/eval.rs` (`SPECIAL_FUNCTIONS`: IF, IFS, CHOOSE,
+  OFFSET, INDIRECT, INDEX, SUBTOTAL, AGGREGATE, TEXT, LET, LAMBDA, MAP, REDUCE, SCAN, BYROW, BYCOL,
+  MAKEARRAY…), excluding the test-only `ADD2`. Every one is an Excel name.
+- **Working** excludes stubs that return an error by design: the 7 CUBE functions (`#N/A`, no
+  cube connections) and WEBSERVICE and FILTERXML (`#VALUE!`). Excel for Mac also lacks
+  WEBSERVICE and FILTERXML; Excel for Windows has them.
+- The measurement is **presence**. Depth (edge cases matching Excel) is estimated below.
+
+## Coverage
+
+**Measured: 501 / 523 by name (95.8%); 492 / 523 working (94.1%).**
+
+| Category | Excel | Ours | Working | % working | Missing |
+|---|---|---|---|---|---|
+| Statistical | 111 | 107 | 107 | 96% | FORECAST.ETS, FORECAST.ETS.CONFINT, FORECAST.ETS.SEASONALITY, FORECAST.ETS.STAT |
+| Math and trigonometry | 80 | 79 | 79 | 99% | PERCENTOF |
+| Financial | 55 | 51 | 51 | 93% | ODDFPRICE, ODDFYIELD, ODDLPRICE, ODDLYIELD |
+| Engineering | 54 | 54 | 54 | 100% | — |
+| Text | 50 | 47 | 47 | 94% | BAHTTEXT, DETECTLANGUAGE, TRANSLATE |
+| Lookup and reference | 40 | 36 | 36 | 90% | GETPIVOTDATA, IMAGE, RTD, TRIMRANGE |
+| Compatibility | 40 | 40 | 40 | 100% | — |
+| Date and time | 25 | 25 | 25 | 100% | — |
+| Information | 22 | 21 | 21 | 95% | STOCKHISTORY |
+| Logical | 19 | 19 | 19 | 100% | — |
+| Database | 12 | 12 | 12 | 100% | — |
+| Cube | 7 | 7 | 0 | 0% | (all 7 are `#N/A` stubs) |
+| Web | 3 | 3 | 1 | 33% | (WEBSERVICE, FILTERXML are stubs; ENCODEURL works) |
+| Add-in and Automation | 3 | 0 | 0 | 0% | CALL, EUROCONVERT, REGISTER.ID |
+| AI and Python | 2 | 0 | 0 | 0% | COPILOT, PY |
+| **Total** | **523** | **501** | **492** | **94.1%** | 22 missing, 9 stubs |
+
+By the Excel version that introduced them (working / total): before 2010 342 / 360, 2010
+56 / 56, 2013 49 / 51, 2016 1 / 5, 2019 6 / 6, 2021 11 / 11, 2024 22 / 23, Microsoft 365 5 / 11.
+Dynamic-array and LAMBDA-era functions (FILTER, SORT, UNIQUE, XLOOKUP, VSTACK, TAKE, GROUPBY,
+PIVOTBY, REGEXTEST…) are all present.
+
+### Scope of what's missing
+
+| Function(s) | In scope? | Estimate | Note |
+|---|---|---|---|
+| FORECAST.ETS family (4) | yes | 4–6 h | AAA exponential smoothing with seasonality detection; needed for Forecast Sheet too |
+| ODDFPRICE, ODDFYIELD, ODDLPRICE, ODDLYIELD | yes | 2–4 h | Odd first/last period bond maths |
+| GETPIVOTDATA | yes | 2–3 h | Needs the pivot engine's result cache; also the "Generate GetPivotData" option |
+| TRIMRANGE, PERCENTOF, BAHTTEXT | yes | 1–2 h | TRIMRANGE also implies the `.:` trim-ref operators |
+| IMAGE | yes | 3–5 h | Pictures in cells (see PR #105); fetching URLs needs a privacy decision |
+| EUROCONVERT | yes | 0.5 h | Fixed conversion table |
+| CUBE* (7), WEBSERVICE, FILTERXML | partly | 4–8 h | FILTERXML can work offline; CUBE needs an OLAP/data-model source |
+| TRANSLATE, DETECTLANGUAGE, STOCKHISTORY, COPILOT, PY | no (cloud) | — | Microsoft cloud services; open equivalents only by owner decision |
+| CALL, REGISTER.ID, RTD | no | — | Native DLL/COM calls; not portable or safe |
+
+## Formula language
+
+| Feature | Status |
+|---|---|
+| A1 and R1C1 references, absolute/relative/mixed, F4 cycling | done |
+| 3-D references (`Sheet1:Sheet3!A1`) | done; endpoint-deletion bug (#140) |
+| Structured references (`Table1[Col]`, `[#Totals]`, `@`) | done |
+| Defined names (workbook and sheet scope), Create from Selection | done |
+| Dynamic arrays, spill, `#SPILL!`, spill operator `A1#` | done; stale-spill bugs (#133, #139; PRs #148, #157) |
+| Implicit intersection `@`, legacy CSE array formulas | done; legacy array range fill (PR #156) |
+| LET, LAMBDA, named LAMBDAs, ISOMITTED, MAP/REDUCE/SCAN/BYROW/BYCOL/MAKEARRAY | done |
+| Iterative calculation for circular references | cycle detection done; the Enable Iterative Calculation setting is stored and saved to XLSX, but the calc engine does not iterate (circular references stay unresolved) |
+| 15-significant-digit comparison semantics | **missing** (#57: `=0.1+0.2=0.3` is FALSE) |
+| External workbook references (`[Book.xlsx]Sheet1!A1`) | parsed; links dropped on open, no update |
+| Localized function names and `;` separators | **missing** (#45); en-US only |
+| Error values | the seven classic errors plus `#SPILL!`, `#CALC!`, `#GETTING_DATA` done; `#FIELD!`, `#BLOCKED!`, `#CONNECT!`, `#BUSY!`, `#UNKNOWN!`, `#PYTHON!` missing (minor: they come from data types, cloud and Python features) |
+
+## Depth (estimated)
+
+**~82% ready.** The library is broad and has 96 test functions in `crates/functions` with many
+assertions each, but there is no conformance suite against Excel-computed results, and user
+reports keep finding edge cases: MIN() with no arguments (#138), COUNTBLANK past the used range
+(#137), ROUND at 15 digits and DATE(1900,2,29) (fixed 10-09), SUMIF sum-range sizing (fixed
+10-09). Statistical distributions and financial functions with iterative solvers (RATE, IRR,
+XIRR, YIELD) are the highest-risk for last-digit differences.
+
+Work to close (18–30 h in total): the in-scope missing functions (12–20 h with the table above),
+an oracle corpus of Excel-computed results per function (owner runs Excel on generated
+workbooks; results checked in as data, not Excel files) and fixing what it finds (6–10 h).
+
+## Revision history
+
+| Date | Change | Summary |
+|---|---|---|
+| 2026-10-10 | major | Created: 501 / 523 by name, 492 working, per category, against Microsoft's published list |