diff --git a/packages/tamarin-prover/build.sh b/packages/tamarin-prover/build.sh
index a484a1ba..4ba93a89 100755
--- a/packages/tamarin-prover/build.sh
+++ b/packages/tamarin-prover/build.sh
@@ -67,6 +67,41 @@ grep -v '^with-compiler:' stackage-lts-24.50.cabal.config > lts-pinned.config
 # so the field is reachable via the type. (pkgmgr-rs#528)
 sed -i 's/defaultTheoryLoadOptions, maudePath, TheoryLoadError/defaultTheoryLoadOptions, TheoryLoadOptions(maudePath), TheoryLoadError/' src/Main/REPL.hs
 
+# Reproducibility: tamarin's version banner embeds the WALL-CLOCK compile time
+#
+#     Git revision: UNKNOWN, branch: UNKNOWN
+#     Compiled at: 2026-07-25 03:47:54.541898723 UTC
+#
+# via a TemplateHaskell splice that calls getCurrentTime while COMPILING. It
+# asks the clock directly, so the sandbox's SOURCE_DATE_EPOCH never reaches it,
+# and two builds differ by exactly that string — measured: 26 bytes out of
+# 135 MB, with the Haskell codegen itself bit-identical. (The git fields are
+# already deterministic: no repo here, so both builds say UNKNOWN.)
+#
+# Rewrite the splice to a fixed instant derived from SOURCE_DATE_EPOCH. Located
+# by content rather than by path so an upstream file move fails loudly here
+# instead of silently reverting to a wall clock.
+STAMP="$(date -u -d "@${SOURCE_DATE_EPOCH:-0}" '+%Y-%m-%d %H:%M:%S UTC' 2>/dev/null \
+        || date -u -r "${SOURCE_DATE_EPOCH:-0}" '+%Y-%m-%d %H:%M:%S UTC')"
+stamp_file="$(grep -rl 'Compiled at' --include='*.hs' src lib 2>/dev/null | head -1)"
+if [ -z "$stamp_file" ]; then
+    echo "ERROR: no source file embeds 'Compiled at' — tamarin's version banner moved; revisit this patch." >&2
+    exit 1
+fi
+# Replace the compile-time-clock splice with the pinned literal. Upstream
+# COMPOSES the action rather than naming it bare:
+#     $(stringE =<< runIO (show `fmap` Data.Time.getCurrentTime))
+# so the first pattern matches the whole parenthesised argument. The two bare
+# forms are kept in case upstream simplifies back to them.
+sed -i "s|runIO ([^)]*getCurrentTime[^)]*)|pure (\"$STAMP\")|g; \
+        s|runIO Data\.Time\.getCurrentTime|pure (\"$STAMP\")|g; \
+        s|runIO getCurrentTime|pure (\"$STAMP\")|g" "$stamp_file"
+if grep -q 'getCurrentTime' "$stamp_file"; then
+    echo "ERROR: tamarin compile-time-clock patch did not apply in $stamp_file (splice shape changed)." >&2
+    grep -n 'getCurrentTime' "$stamp_file" >&2
+    exit 1
+fi
+
 # Build + install the executable (STATIC — a normal Haskell static link; the link
 # was never the problem). The sandbox hides build detail, so on failure dump the
 # real error (compile OR link) rather than a silent "Failed to build".
diff --git a/packages/zola/build.sh b/packages/zola/build.sh
index c20b192c..9453acf1 100755
--- a/packages/zola/build.sh
+++ b/packages/zola/build.sh
@@ -3,9 +3,20 @@
 set -eu
 export CC=gcc
 export LD=gcc
-# Reproducibility (per minimal-repro's guide): strip absolute build
-# paths (source dir + cargo registry) and disable incremental builds.
-export RUSTFLAGS="-C linker=gcc --remap-path-prefix=$(pwd)=/builddir --remap-path-prefix=$HOME/.cargo=/cargo"
+# Reproducibility (per minimal-repro's guide): strip absolute build paths
+# (source dir + cargo registry), disable incremental builds, and pin codegen.
+#
+# codegen-units=1 is the load-bearing one here. rustc's default release build
+# shards codegen across parallel units, and the units finish in whatever order
+# the thread pool happens to produce, so functions are EMITTED in a different
+# order each build. The result is a binary of identical size whose contents are
+# a permutation of themselves — measured on 0.22.1: 16.89% of bytes differed
+# with the total size unchanged, and 69% of the differing windows had a
+# byte-exact twin elsewhere in the other build. Not codegen variance; ordering.
+#
+# symbol-mangling-version=v0 removes the other half: the legacy mangling scheme
+# embeds a compilation-session hash in symbol names, which varies run to run.
+export RUSTFLAGS="-C linker=gcc --remap-path-prefix=$(pwd)=/builddir --remap-path-prefix=$HOME/.cargo=/cargo -C codegen-units=1 -C symbol-mangling-version=v0"
 export CARGO_INCREMENTAL=0
 cargo build --release
 mkdir -p "$OUTPUT_DIR/usr/bin"