Spreadsheet String Concatenation with Dependent Cells

Implement a 26-column, 100-row spreadsheet that stores strings and supports formulas that concatenate other cells. When a referenced cell changes, future reads of dependent formulas must reflect the new string. Use columns `A` through `Z` and rows `1` through `100`. Implement `concatenate_sheet(operations: string[][]) -> string[]`: - `["set", cell, raw]` stores a literal string or formula and returns the string `"OK"`. - A raw value starting with `=` is a formula, such as `=C1C2`, which concatenates the computed values of `C1` and `C2` in that order. - `["get", cell]` returns `"VALUE:"` followed by the computed string, or exactly `"CYCLE"` if the read reaches a circular reference. - Return one string per operation. The `VALUE:` prefix is part of the output contract and distinguishes arbitrary literal content from error/status tokens. ### Constraints & Assumptions - The fixed grid size and concatenation form are the reported variant; the following parsing and error rules make the practice task deterministic. - A formula is `=` followed by one or more valid cell names with no separators or spaces. Each name has exactly one uppercase column letter followed by a decimal row number without leading zero. - Repeated references repeat the corresponding string. Formula order matters. - A literal does not start with `=`. Unset cells evaluate to the empty string, so getting one returns `"VALUE:"`. - Set replaces the old literal or formula completely. Cycles are stored and diagnosed on reads that reach them; an unrelated cycle does not affect another cell. - There are at most 500 operations, at most 20 references per formula, and at most 100 characters per literal. Every successfully evaluated cell has a computed length of at most 10,000 characters. - All inputs follow the grammar and grid bounds. Persistent stale caches must not survive an input update. ### Examples ```text operations = [ ["set","C1","hello"], ["set","C2"," world"], ["set","A1","=C1C2"], ["get","A1"], ["set","C1","goodbye"], ["get","A1"] ] result = ["OK","OK","OK","VALUE:hello world","OK","VALUE:goodbye world"] ``` ```text operations = [["set","A1","=B1B1"],["set","B1","=A1"],["get","A1"]] result = ["OK","OK","CYCLE"] ``` ```hint Parse references before evaluating them The next uppercase letter starts the next cell reference. Preserve the resulting reference sequence even if a separate dependency set is used for cycle detection. ```