diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e930ff5e35..b9a7117688 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -55,6 +55,13 @@ the full dev/release/dist taxonomy and the slim `--features dev-cli` CLI (#5422)
 
 The full README [Development](README.md#development) section has more `cargo run` recipes (HIR dumps, per-crate rebuilds).
 
+For fixture-only parity reruns, `PERRY_SKIP_BUILD=1 ./run_parity_tests.sh`
+reuses `PERRY_BIN` and the matching runtime/stdlib archives from
+`PERRY_RUNTIME_DIR` (or the binary's directory) with auto-optimization disabled.
+Rebuild instead whenever Rust or Cargo inputs, or compiler, runtime, stdlib, or
+required extension sources differ; reuse does not prove that prebuilt artifacts
+match the checkout.
+
 ## Making changes
 
 ### What goes in a PR
diff --git a/run_parity_tests.sh b/run_parity_tests.sh
index 5546921045..8dd7b536be 100755
--- a/run_parity_tests.sh
+++ b/run_parity_tests.sh
@@ -417,8 +417,37 @@ echo ""
 # release binary the prior step had just produced, and (b) adds cargo's own
 # per-invocation overhead × ~150 tests.
 TARGET_DIR="${CARGO_TARGET_DIR:-$SCRIPT_DIR/target}"
-PERRY_BIN="$TARGET_DIR/release/perry"
-echo "Building compiler (release)..."
+PERRY_SKIP_BUILD="${PERRY_SKIP_BUILD:-0}"
+case "$PERRY_SKIP_BUILD" in
+    0|1) ;;
+    *)
+        echo -e "${RED}Invalid PERRY_SKIP_BUILD '$PERRY_SKIP_BUILD' (want 0 or 1)${NC}" >&2
+        exit 1
+        ;;
+esac
+
+if [[ "$PERRY_SKIP_BUILD" == "1" ]]; then
+    PERRY_BIN="${PERRY_BIN:-$TARGET_DIR/release/perry}"
+    if [[ ! -x "$PERRY_BIN" ]]; then
+        echo -e "${RED}PERRY_BIN is not executable: $PERRY_BIN${NC}" >&2
+        exit 1
+    fi
+    PERRY_RUNTIME_DIR="${PERRY_RUNTIME_DIR:-$(cd "$(dirname "$PERRY_BIN")" && pwd)}"
+    case "$(uname -s)" in
+        MINGW*|MSYS*|CYGWIN*) runtime_lib=perry_runtime.lib; stdlib_lib=perry_stdlib.lib ;;
+        *) runtime_lib=libperry_runtime.a; stdlib_lib=libperry_stdlib.a ;;
+    esac
+    if [[ ! -f "$PERRY_RUNTIME_DIR/$runtime_lib" || ! -f "$PERRY_RUNTIME_DIR/$stdlib_lib" ]]; then
+        echo -e "${RED}PERRY_RUNTIME_DIR must contain $runtime_lib and $stdlib_lib: $PERRY_RUNTIME_DIR${NC}" >&2
+        exit 1
+    fi
+    export PERRY_RUNTIME_DIR PERRY_NO_AUTO_OPTIMIZE=1
+    echo "Using prebuilt compiler: $PERRY_BIN"
+    echo "Using prebuilt runtime archives: $PERRY_RUNTIME_DIR"
+else
+    PERRY_BIN="$TARGET_DIR/release/perry"
+    echo "Building compiler (release)..."
+fi
 BUILD_PACKAGES=(-p perry -p perry-runtime -p perry-stdlib -p perry-runtime-static -p perry-stdlib-static)
 BUILD_FEATURES=()
 needs_wasm_host=0
@@ -498,11 +527,11 @@ if [[ "${#BUILD_FEATURES[@]}" -gt 0 ]]; then
     feature_csv=$(IFS=,; echo "${BUILD_FEATURES[*]}")
     BUILD_FEATURE_ARGS=(--features "$feature_csv")
 fi
-if ! cargo build --release --quiet "${BUILD_PACKAGES[@]}" "${BUILD_FEATURE_ARGS[@]}" 2>/dev/null; then
+if [[ "$PERRY_SKIP_BUILD" == "0" ]] && ! cargo build --release --quiet "${BUILD_PACKAGES[@]}" "${BUILD_FEATURE_ARGS[@]}" 2>/dev/null; then
     echo -e "${RED}Failed to build compiler/runtime archives${NC}"
     exit 1
 fi
-if [[ "$needs_wasm_host" -eq 1 ]]; then
+if [[ "$PERRY_SKIP_BUILD" == "0" && "$needs_wasm_host" -eq 1 ]]; then
     # WebAssembly metadata fixtures exercise the real host shims. Build the
     # wasm-enabled runtime staticlib after the CLI build above; enabling this
     # feature while building the `perry` binary would make the CLI link against
@@ -513,7 +542,7 @@ if [[ "$needs_wasm_host" -eq 1 ]]; then
         exit 1
     fi
 fi
-if [[ "$needs_ext_net" -eq 1 ]]; then
+if [[ "$PERRY_SKIP_BUILD" == "0" && "$needs_ext_net" -eq 1 ]]; then
     echo "Building net extension (release)..."
     ext_net_jobs="${CARGO_BUILD_JOBS:-1}"
     if ! cargo build --release --quiet -p perry-ext-net -j "$ext_net_jobs" 2>/dev/null; then
@@ -526,7 +555,11 @@ if [[ ! -x "$PERRY_BIN" ]]; then
     exit 1
 fi
 
-echo -e "${GREEN}Compiler and runtime archives built successfully${NC}"
+if [[ "$PERRY_SKIP_BUILD" == "0" ]]; then
+    echo -e "${GREEN}Compiler and runtime archives built successfully${NC}"
+else
+    echo -e "${GREEN}Prebuilt compiler and runtime archives verified${NC}"
+fi
 echo ""
 echo "Running parity tests (backend: $BACKEND_LABEL, suite: $TEST_SUITE${MODULE_FILTER:+, module: $MODULE_FILTER})..."
 echo ""
diff --git a/tests/test_parity_build_reuse.sh b/tests/test_parity_build_reuse.sh
new file mode 100755
index 0000000000..5d9a28c5d1
--- /dev/null
+++ b/tests/test_parity_build_reuse.sh
@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+WORK="$(mktemp -d)"
+trap 'rm -rf "$WORK"' EXIT
+
+cp "$ROOT/run_parity_tests.sh" "$WORK/run_parity_tests.sh"
+mkdir -p "$WORK/bin" "$WORK/test-files" "$WORK/test-parity/node-suite/reuse" \
+    "$WORK/test-parity/output/node" "$WORK/test-parity/output/perry" "$WORK/test-parity/reports"
+cat > "$WORK/bin/cargo" <<'EOF'
+#!/bin/sh
+echo invoked >> "$CARGO_LOG"
+exit 99
+EOF
+cat > "$WORK/perry" <<'EOF'
+#!/bin/sh
+echo "$0|$PERRY_RUNTIME_DIR|$PERRY_NO_AUTO_OPTIMIZE" >> "$PERRY_LOG"
+while [ "$#" -gt 0 ]; do
+    if [ "$1" = "-o" ]; then
+        cat > "$2" <<'BIN'
+#!/bin/sh
+echo reuse-ok
+BIN
+        chmod +x "$2"
+        exit 0
+    fi
+    shift
+done
+exit 0
+EOF
+cat > "$WORK/bin/node" <<'EOF'
+#!/bin/sh
+echo reuse-ok
+EOF
+cat > "$WORK/bin/ps" <<'EOF'
+#!/bin/sh
+echo 1
+EOF
+touch "$WORK/test-parity/node-suite/reuse/basic.ts"
+chmod +x "$WORK/bin/cargo" "$WORK/bin/node" "$WORK/bin/ps" "$WORK/perry"
+export PATH="$WORK/bin:$PATH" CARGO_LOG="$WORK/cargo.log" PERRY_LOG="$WORK/perry.log"
+
+run_failure() {
+    local expected=$1
+    shift
+    if "$@" >"$WORK/output" 2>&1; then
+        echo "expected failure: $expected" >&2
+        exit 1
+    fi
+    grep -F "$expected" "$WORK/output" >/dev/null
+}
+
+run_failure "Invalid PERRY_SKIP_BUILD 'yes'" env PERRY_SKIP_BUILD=yes "$WORK/run_parity_tests.sh"
+run_failure "PERRY_BIN is not executable" env PERRY_SKIP_BUILD=1 PERRY_BIN="$WORK/missing" "$WORK/run_parity_tests.sh"
+mkdir -p "$WORK/empty"
+case "$(uname -s)" in
+    MINGW*|MSYS*|CYGWIN*) touch "$WORK/empty/perry_runtime.lib" ;;
+    *) touch "$WORK/empty/libperry_runtime.a" ;;
+esac
+run_failure "PERRY_RUNTIME_DIR must contain" env PERRY_SKIP_BUILD=1 PERRY_BIN="$WORK/perry" PERRY_RUNTIME_DIR="$WORK/empty" "$WORK/run_parity_tests.sh"
+
+case "$(uname -s)" in
+    MINGW*|MSYS*|CYGWIN*) touch "$WORK/perry_runtime.lib" "$WORK/perry_stdlib.lib" ;;
+    *) touch "$WORK/libperry_runtime.a" "$WORK/libperry_stdlib.a" ;;
+esac
+: > "$CARGO_LOG"
+set +e
+PERRY_SKIP_BUILD=1 PERRY_BIN="$WORK/perry" "$WORK/run_parity_tests.sh" --suite node-suite --module reuse >"$WORK/output" 2>&1
+status=$?
+set -e
+[[ "$status" -eq 0 ]]
+grep -F "Using prebuilt compiler: $WORK/perry" "$WORK/output" >/dev/null
+grep -F "Using prebuilt runtime archives: $WORK" "$WORK/output" >/dev/null
+grep -F "$WORK/perry|$WORK|1" "$PERRY_LOG" >/dev/null
+[[ ! -s "$CARGO_LOG" ]]
+
+echo "PASS"