Merge PR #2019: Formulas: the reference app's longest legal operator chain (4,096 operands) no longer crashes entry or save

docs/function-parity.md: union of the status line and both history rows.

docs/function-parity.md

@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **Last reviewed:** 2026-10-15 · **Last updated:** 2026-10-19 · **Change:** minor (LET and LAMBDA names ignore case in any script) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-15 · **Last updated:** 2026-10-19 · **Change:** minor (LET and LAMBDA names ignore case in any script; flat operator chains as long as Excel allows: 4,096 operands no longer overflow the stack, Spanish entry accepts them, files keep them as plain formulas); previously minor (MEDIAN and AGGREGATE median avoid intermediate overflow) · **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).
@@ -84,6 +84,7 @@ PIVOTBY, REGEXTEST…) are all present.
 | 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 |
+| Long flat operator chains (`=A1+A2+…`, `-`, `*`, `/`, `^`, `&`, comparisons) | done: no operand limit below Excel's 8,192-character formula limit (Excel, observed: `=1+1+…` with 4,096 operands is exactly 8,192 characters with the `=` and calculates; one more character is refused). Evaluated (#484), printed (#628), stored, copied, adjusted, saved and reopened without recursing once per operand, on a 1 MiB stack (#916); written to XLSX as plain formulas, not dynamic arrays; Spanish entry accepts them |
 | 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)
@@ -115,6 +116,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 | Date | Change | Summary |
 |---|---|---|
 | 2026-10-19 | minor | LET and LAMBDA names compare case-insensitively in any script, as in Excel: `=LET(dług,100,DŁUG*2)` is 200 (was #NAME?); also LET-bound lambdas called or passed by name (`żar(2)`, `MAP(…,Λ)`), `ISOMITTED`, and formula-bar alias translation (one shared `gridcraft_formula::same_name`, which matches `ß` with `ẞ` and keeps dotless `ı` apart from `i`) |
+| 2026-10-19 | minor | Long flat operator chains (#916): 4,096 operands (Excel's 8,192-character limit) no longer overflow the stack when entered, filled, adjusted or saved; chains past 64 operands are no longer saved as dynamic-array formulas; Spanish entry no longer refuses chains past 256 operands |
 | 2026-10-15 | minor | MEDIAN and AGGREGATE median use an overflow-safe midpoint (#1579); regressions cover finite extremes, tiny values and dependent recalculation |
 | 2026-10-13 | minor | Clear reports changed stored cells sparsely, including those beyond the first million coordinates; dependent formulas and removed spills update, while clearing empty merges still unblocks spills (#1032) |
 | 2026-10-12 | minor | USDOLLAR added as a Compatibility function (not on Microsoft's list, so the counts don't change); MIRR with no positive flow is -1, COUNTIF's bare `"<="` / `">="` skip empty strings, INDIRECT with `a1` = FALSE gives `#REF!` for A1-style text (#738) |