FormatStatus now matches named codes against code & 0xFFFF0000 (high-word
mask) rather than exact equality, so status codes carrying sub-code or flag
bits in the low 16 bits (e.g. 0x80050001) still resolve to their named class.
For codes not in the named shortlist a severity-class fallback using the top
2 bits always emits Good / Uncertain / Bad rather than bare hex.
Updated the stale FormatStatus_unknown_codes_fall_back_to_hex_only test (its
expectation became invalid once the severity-class fallback was added) and
added new Theory cases exercising both the high-word matching and the
severity-class fallback paths.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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