When crafter-build's stdout is not a TTY (redirected to a file or pipe) the
C runtime defaults to full (block) buffering. The progress path is TTY-aware
and the in-place redraw flushes explicitly, but the non-TTY append path
(`[N/M]` lines), Finalize()'s `Built N steps` line and the `-r` server's
`listening on port :N` line all go through block-buffered stdout with no
flush. They accumulate in the buffer and only spill at ~4KB boundaries.
On a normal build this is hidden because the C runtime flushes stdout at
exit. Under `-r` the process never exits — it blocks in its serve loop — so
the trailing buffer is never flushed: a redirected log freezes mid-build (or
sits at 0 bytes) even though the build finished and the server is already
answering. Any tooling that polls the log for `Built …` / `listening …` /
`[N/N]` hangs forever. This is the real cause of the frozen log misdiagnosed
as a build deadlock in #16.
Fix: switch stdout to line buffering at the very top of main(), before any
output, only when stdout is not a terminal. Every `\n` then flushes, so the
markers reach a redirected log immediately. No behaviour change on a TTY.
Kept self-contained in main.cpp using system headers (isatty + setvbuf)
rather than a new Crafter::Progress export: the self-hosting exe build
compiles main.cpp against the installed/cached Crafter.Build module BMIs,
which shadow the freshly built local ones, so a new interface symbol would
not be visible without reinstalling crafter-build first.
Resolves#18
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
