Warm fasl cache duplicates the output of nested (load)s #92

Found while running capcov's f-modelcheck workload across ports. It reproduces on main e3dec8b (LuaJIT 2.1.1785763465, macOS arm64). The #84–#88 PRs (#89, #90, #91) don't cause it.

Repro

mkdir fasl-dup && cd fasl-dup
printf '(output "LIB~%%")\n' > lib.shen
printf '(output "BEGIN~%%")\n(load "lib.shen")\n(define reload X -> (load X))\n(reload "lib.shen")\n(output "END~%%")\n' > main.shen
export SHEN_FASL_DIR=$PWD/fasl
for i in 1 2 3; do shen --hush-load main.shen | tr '\n' '|'; echo; done

Output at e3dec8b:

BEGIN|LIB|LIB|END|              <- cold fasl cache: correct
BEGIN|LIB|LIB|LIB|LIB|END|      <- warm: every LIB is printed twice
BEGIN|LIB|LIB|LIB|LIB|END|

Control: with SHEN_FASL=off the output is BEGIN|LIB|LIB|END| on every run. shen-go 1f587de prints LIB twice, plus its load echo.

A plain top-level (load "lib.shen") in main.shen has the same problem. With main.shen as (output "BEGIN~%") (load "lib.shen") (load "lib.shen") (output "END~%"), the cold run prints BEGIN|LIB|LIB|END| and the warm run prints BEGIN|LIB|LIB|LIB|LIB|END|. So the trigger is output inside a file that a cached file loads; it doesn't matter where the nested load is called from. My guess is that on a fasl hit for main.shen, the replay emits the nested file's output once from the outer record stream and again from the nested load. I haven't confirmed this.

Impact

capcov f-modelcheck registers its judges with (load Path) from inside mc.judge-all. Its first run prints 25 MC lines, identical to shen-go. Every later run prints 36: 11 JUDGE/PASS lines are duplicated. The workload's result therefore depends on the state of the cache.

Generated by Claude Code