fuzz_test.sh: copy the binary to a private path before looping

A concurrent gmake clean (update_head_reference.sh, precommit_check.sh)
unlinks ./_typhoon out from under a fuzz loop mid-run, breaking every
subsequent iteration with "not found/executable". Observed live running
this alongside update_head_reference.sh today. Copy once up front instead
of exec'ing $BIN in place, so later rebuilds in the working tree can't
touch what the loop is actually running.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/fuzz_test.sh b/src/fuzz_test.sh
index 5e3d5f7..131b6a0 100755
--- a/src/fuzz_test.sh
+++ b/src/fuzz_test.sh
@@ -27,6 +27,19 @@ if [ ! -f "$SUITE" ]; then
     exit 1
 fi
 
+# Copy the binary out to a stable, private path rather than exec'ing $BIN
+# in place. A concurrent "gmake clean" (e.g. update_head_reference.sh,
+# precommit_check.sh) unlinks ./_typhoon/./typhoon out from under a loop
+# that's mid-run, silently breaking every subsequent iteration with
+# "not found/executable" -- observed live running this alongside
+# update_head_reference.sh. Copying once up front means later rebuilds in
+# the working tree can't touch what this loop is actually running.
+FUZZ_BIN="$LOGDIR/fuzz_bin_$$"
+cp "$BIN" "$FUZZ_BIN"
+chmod +x "$FUZZ_BIN"
+trap 'rm -f "$FUZZ_BIN"' EXIT
+BIN="$FUZZ_BIN"
+
 TOTAL_RECORDS=$(grep -c '^go' "$SUITE")
 
 ITER=0