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Usman Akinyemi
b0e65da2af
Detect the `{ident?}` pattern where `?` is immediately followed by `}` and emit
a clearer diagnostic explaining that `:` is required for Debug formatting.
This avoids falling back to a generic “invalid format string” error and adds
a targeted UI test for the case.
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>