Every fec error message was written to stderr, and COMMAND.COM can only
redirect handle 1 -- ">" is the whole vocabulary, "2>" is not parsed at all.
So a failing compile recorded exit code 1 and a zero-byte log, and the actual
message went to a screen nobody reads. Confirmed directly: `FEC.EXE --check`
on a fixture that must fail produced rc=1 and 0 bytes of stdout.
That is why an unexpected compiler failure was undiagnosable. It also means
the M6 reject cases have only ever asserted "exit code was nonzero" -- the
error text they nominally check has never been observable to the runner.
Add fe_diag_stream(), which resolves once to stdout when FE_DIAG_STDOUT is set
and stderr otherwise, and route diag.c and driver.c through it. The default is
unchanged, so interactive use keeps writing to stderr; the runner sets the
variable in RUN.BAT. The stderr references in check.c and emit_c.c are the
Ferro language's own std.io.stderr writer and are deliberately untouched.
Verified in DOSBox-X: 155 passed. A rejecting compile now records its message,
source excerpt and caret in RESULTS\<key>.LOG.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BScg8CF1sAAM2zVHAu5zvW
coolguyandClaude Opus 5