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

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"]

operations = [["set","A1","=B1B1"],["set","B1","=A1"],["get","A1"]]
result = ["OK","OK","CYCLE"]