D091 - A writer refuses where a reader may guess

Status: decided Date: 2026-09-26

Code whose output is written back into a file refuses input it cannot represent exactly: dynlib::string_at returns BuildError::SymbolName for an out-of-range offset, a missing terminator or invalid UTF-8. A reader may be lenient where leniency can only produce a wrong line of output.

Why: a reader's guess is a wrong line on a terminal; a writer's guess is a wrong file. A lossy builder renamed symbols and, given the wrong string table, wrote undefined symbols back as nameless locals, skipping the unclaimed-import check.

Rejected:

• One permissiveness for both sides: either the reader refuses real files or the writer invents names.