diff --git a/.agents/skills/guardian-validation-matrix/references/command-matrix.md b/.agents/skills/guardian-validation-matrix/references/command-matrix.md
index b74969ec..9cb3b677 100644
--- a/.agents/skills/guardian-validation-matrix/references/command-matrix.md
+++ b/.agents/skills/guardian-validation-matrix/references/command-matrix.md
@@ -90,10 +90,13 @@ Code in:
 
 Run:
 ```bash
+./scripts/preflight-browser-smoke.sh
 cd examples/smoke-web && npm run typecheck && npm run build
 cd examples/web && npm run build
 ```
 
+The preflight is required after any branch switch: these apps alias the SDK packages to `packages/*/dist/index.js`, and `dist/` is gitignored, so a build left over from another protocol line survives the checkout and fails only at MASM compile time.
+
 Manual canary:
 - use `smoke-test-ts-multisig-sdk`
 
diff --git a/.agents/skills/smoke-test-ts-multisig-sdk/SKILL.md b/.agents/skills/smoke-test-ts-multisig-sdk/SKILL.md
index 9c2f8ea8..ceedce91 100644
--- a/.agents/skills/smoke-test-ts-multisig-sdk/SKILL.md
+++ b/.agents/skills/smoke-test-ts-multisig-sdk/SKILL.md
@@ -29,7 +29,7 @@ If the commitment does not round-trip into `status().multisig.guardianPubkey` af
 
 ## Testing Deployed SDKs
 
-`examples/smoke-web/package.json` pins `@openzeppelin/miden-multisig-client` and `@openzeppelin/guardian-client` to `file:../../packages/...`, so `npm run dev` smokes the **workspace source**, not the npm release. When the user asks to smoke "the deployed SDK" or "the released version":
+`examples/smoke-web/package.json` pins `@openzeppelin/miden-multisig-client` and `@openzeppelin/guardian-client` to `file:../../packages/...`, and `vite.config.ts` additionally aliases both to `packages/<name>/dist/index.js`. So `npm run dev` smokes the **workspace build output**, not the npm release and not `src/`. When the user asks to smoke "the deployed SDK" or "the released version":
 
 1. Create a scratch Vite (or equivalent) project outside the workspace (e.g. `/tmp/guardian-ts-smoke-<version>`).
 2. Declare the published packages pinned to the release under test:
@@ -48,6 +48,24 @@ If the commitment does not round-trip into `status().multisig.guardianPubkey` af
 
 Treat workspace-path smoke-web runs and deployed-npm scratch-project runs as different smoke targets. Never collapse them in the report.
 
+## Stale Build Output
+
+`packages/*/dist` is gitignored, so `git checkout` never touches it. A dist built on another protocol line (for example a `miden-0.16` branch) keeps being served on a 0.15 branch until something rebuilds it, and the apps load `dist`, not `src`. Nothing in a source-level check can see this.
+
+The signature is a MASM assembler error at account creation, most often:
+
+```text
+Failed to compile account component: invalid syntax
+```
+
+That means the MASM baked into the stale `dist` is a different dialect from the `@miden-sdk/miden-sdk` WASM assembler the app loaded. Cross-line MASM differences to look for: the `openzeppelin::auth::*` namespace versus `miden::standards::auth::*`, and `pub use multisig::name` versus `pub use {name} from module`.
+
+The same applies to `node_modules`: another branch can leave an out-of-range `@miden-sdk/miden-sdk` installed that the workspace's own lockfile does not pin. Compare installed against the lockfile, not against the `package.json` range, because a caret range hides it.
+
+`./scripts/preflight-browser-smoke.sh` detects and repairs both. Rebuild with `npm run clean && npm run build`, never a bare `build`: export names differ across lines, so `tsc` alone leaves orphaned files from the previous build. Restart any running dev server afterwards, and clear `examples/*/node_modules/.vite`.
+
+Do not report this class of failure as an SDK or contract bug until the preflight passes.
+
 ## Browser Automation
 
 The smoke harness is designed to be driven from DevTools (`window.smoke.*`), which makes it drivable by browser-automation tools when available. Prefer in this order:
@@ -71,29 +89,34 @@ When reporting, capture the concrete tool invocation path used (Chrome MCP vs Cl
    - `examples/_shared/multisig-browser/src/multisigApi.ts`
    - `examples/_shared/multisig-browser/src/initClient.ts`
    - `examples/smoke-web/src/App.tsx`
-2. Run targeted TypeScript validation before manual smoke:
+2. Run the browser preflight before anything else. It is mandatory after any branch switch:
+   ```bash
+   ./scripts/preflight-browser-smoke.sh
+   ```
+   It reports, fixes, then re-verifies two things source-level checks cannot see: a workspace whose installed `@miden-sdk/miden-sdk` does not match its own lockfile pin, and a `packages/*/dist` older than its `src`. Use `--check` to report without writing. See Stale Build Output below for why this class of failure is silent.
+3. Run targeted TypeScript validation before manual smoke:
    ```bash
    cd packages/miden-multisig-client && npm test
    cd examples/smoke-web && npm run typecheck && npm run build
    cd examples/web && npm run build
    ```
-3. Start one GUARDIAN server from the repo root:
+4. Start one GUARDIAN server from the repo root:
    ```bash
    cargo run -p guardian-server --bin server
    ```
-4. Start the smoke harness:
+5. Start the smoke harness:
    ```bash
    cd examples/smoke-web && npm run dev
    ```
-5. Open the smoke harness in separate real browsers or fully isolated browser profiles. Do not rely on same-profile parallel tabs. Prefer Chrome + Brave or Chrome + Firefox when driving concurrent cosigners.
-6. Let the page-load bootstrap settle first. If `await window.smoke.status()` is not `ready`, or you need to override the default endpoints or signer settings, initialize the session with `window.smoke.initSession(...)`.
-7. Default to local signers and Falcon unless the prompt explicitly asks for ECDSA, Para, or Miden Wallet.
-8. Record each browser's signer commitment from `await window.smoke.status()` before account creation.
-9. Create the multisig in one browser by passing the other browsers' commitments to `createAccount`.
-10. Load and sync the account in the other browsers with `loadAccount` and `sync`.
-11. Choose the smallest workflow from `references/workflow-matrix.md`.
-12. Record the exact browser/profile labels, endpoints, signer source, signature scheme, workflow, observed result, and timing data.
-13. Compare the recorded timings with `references/timing-baseline.md`.
+6. Open the smoke harness in separate real browsers or fully isolated browser profiles. Do not rely on same-profile parallel tabs. Prefer Chrome + Brave or Chrome + Firefox when driving concurrent cosigners.
+7. Let the page-load bootstrap settle first. If `await window.smoke.status()` is not `ready`, or you need to override the default endpoints or signer settings, initialize the session with `window.smoke.initSession(...)`.
+8. Default to local signers and Falcon unless the prompt explicitly asks for ECDSA, Para, or Miden Wallet.
+9. Record each browser's signer commitment from `await window.smoke.status()` before account creation.
+10. Create the multisig in one browser by passing the other browsers' commitments to `createAccount`.
+11. Load and sync the account in the other browsers with `loadAccount` and `sync`.
+12. Choose the smallest workflow from `references/workflow-matrix.md`.
+13. Record the exact browser/profile labels, endpoints, signer source, signature scheme, workflow, observed result, and timing data.
+14. Compare the recorded timings with `references/timing-baseline.md`.
 
 ## Baseline Harness
 
diff --git a/.agents/skills/smoke-test-ts-multisig-sdk/references/workflow-matrix.md b/.agents/skills/smoke-test-ts-multisig-sdk/references/workflow-matrix.md
index ad777c75..43d5f541 100644
--- a/.agents/skills/smoke-test-ts-multisig-sdk/references/workflow-matrix.md
+++ b/.agents/skills/smoke-test-ts-multisig-sdk/references/workflow-matrix.md
@@ -6,14 +6,17 @@ Map the changed area to the smallest browser smoke workflow that still proves th
 
 ## Environment
 
-Run validation first:
+Run the preflight first, then validation:
 
 ```bash
+./scripts/preflight-browser-smoke.sh
 cd packages/miden-multisig-client && npm test
 cd examples/smoke-web && npm run typecheck && npm run build
 cd examples/web && npm run build
 ```
 
+The preflight is mandatory after any branch switch. The apps load `packages/*/dist`, which is gitignored and survives checkouts; see Stale Build Output in `SKILL.md`.
+
 Primary smoke server commands:
 
 ```bash
diff --git a/scripts/preflight-browser-smoke.sh b/scripts/preflight-browser-smoke.sh
new file mode 100755
index 00000000..ba8ff4af
--- /dev/null
+++ b/scripts/preflight-browser-smoke.sh
@@ -0,0 +1,220 @@
+#!/usr/bin/env bash
+#
+# Preflight for the browser example harnesses (examples/smoke-web, examples/web).
+#
+# Both apps alias @openzeppelin/miden-multisig-client and @openzeppelin/guardian-client
+# to packages/<name>/dist/index.js in their vite.config.ts, so they run the BUILT
+# package, never src/. dist/ is gitignored, which means it survives every branch
+# switch: a dist built on another protocol line (e.g. miden-0.16) keeps being served
+# on a 0.15 branch until something rebuilds it. The MASM baked into that dist then
+# meets a different WASM assembler and fails with a bare
+# "Failed to compile account component: invalid syntax".
+#
+# The same applies to node_modules: a foreign branch can leave an out-of-range
+# @miden-sdk/miden-sdk installed that the workspace's own lockfile does not pin.
+#
+# This script reports what drifted, fixes it, then re-verifies.
+#
+# Usage:
+#   ./scripts/preflight-browser-smoke.sh          # report, fix, verify
+#   ./scripts/preflight-browser-smoke.sh --check   # report only, never write
+#
+# Exit codes: 0 = clean (or all issues fixed), 1 = drift remains / fix failed,
+#             2 = usage error.
+
+set -uo pipefail
+
+CHECK_ONLY=0
+case "$#" in
+  0) ;;
+  1) case "$1" in
+       --check) CHECK_ONLY=1 ;;
+       *) echo "error: expected --check or no arguments" >&2; exit 2 ;;
+     esac ;;
+  *) echo "error: expected --check or no arguments" >&2; exit 2 ;;
+esac
+
+ROOT="$(git rev-parse --show-toplevel 2>/dev/null)" || {
+  echo "error: not inside a git repository" >&2
+  exit 1
+}
+cd "$ROOT"
+
+# Packages the browser apps alias to dist/index.js. Keep in sync with the
+# resolve.alias blocks in examples/web/vite.config.ts and examples/smoke-web/vite.config.ts.
+DIST_PACKAGES=(
+  packages/guardian-client
+  packages/miden-multisig-client
+)
+
+# Workspaces that declare @miden-sdk/miden-sdk and must match their own lockfile pin.
+SDK_WORKSPACES=(
+  packages/miden-multisig-client
+  examples/_shared/multisig-browser
+  examples/smoke-web
+  examples/web
+  examples/operator-smoke-web
+)
+
+RED=$'\033[31m'; GRN=$'\033[32m'; YEL=$'\033[33m'; DIM=$'\033[2m'; OFF=$'\033[0m'
+[[ -t 1 ]] || { RED=""; GRN=""; YEL=""; DIM=""; OFF=""; }
+
+ok()   { printf '  %s%-46s%s %s\n' "$DIM" "$1" "$OFF" "${GRN}ok${OFF}"; }
+bad()  { printf '  %s%-46s%s %s\n' "$DIM" "$1" "$OFF" "${RED}$2${OFF}"; }
+note() { printf '      %s%s%s\n' "$DIM" "$1" "$OFF"; }
+
+# Version installed in a workspace's node_modules, or empty.
+installed_sdk() {
+  python3 -c "
+import json,sys
+try: print(json.load(open('$1/node_modules/@miden-sdk/miden-sdk/package.json'))['version'])
+except Exception: print('')
+" 2>/dev/null
+}
+
+# Version the workspace's own lockfile pins, or empty.
+locked_sdk() {
+  python3 -c "
+import json,sys
+try:
+    d=json.load(open('$1/package-lock.json'))['packages']
+    print(d.get('node_modules/@miden-sdk/miden-sdk',{}).get('version',''))
+except Exception: print('')
+" 2>/dev/null
+}
+
+declared_sdk() {
+  python3 -c "
+import json,sys
+try:
+    d=json.load(open('$1/package.json'))
+    print(d.get('dependencies',{}).get('@miden-sdk/miden-sdk','') or d.get('devDependencies',{}).get('@miden-sdk/miden-sdk',''))
+except Exception: print('')
+" 2>/dev/null
+}
+
+# Count src/*.ts files newer than the built entrypoint. Echoes STALE reason or empty.
+dist_staleness() {
+  local pkg="$1" entry="$1/dist/index.js"
+  [[ -d "$pkg/dist" ]] || { echo "dist/ missing"; return; }
+  [[ -f "$entry" ]]    || { echo "dist/index.js missing"; return; }
+  local n
+  n=$(find "$pkg/src" -name '*.ts' -newer "$entry" 2>/dev/null | wc -l | tr -d ' ')
+  [[ "$n" -gt 0 ]] && echo "$n src file(s) newer than dist"
+}
+
+SDK_DRIFT=(); LOCK_ERRORS=(); STALE=(); ISSUES=0
+
+scan() {
+  SDK_DRIFT=(); LOCK_ERRORS=(); STALE=()
+
+  printf '\n%s[1/4]%s @miden-sdk/miden-sdk: installed vs lockfile pin\n' "$YEL" "$OFF"
+  for w in "${SDK_WORKSPACES[@]}"; do
+    [[ -d "$w" ]] || continue
+    local dec ins loc
+    dec="$(declared_sdk "$w")"; [[ -n "$dec" ]] || continue
+    ins="$(installed_sdk "$w")"; loc="$(locked_sdk "$w")"
+    if [[ -z "$loc" ]]; then
+      bad "$w" "lockfile pin missing"
+      note "declared $dec -> run npm install to update package-lock.json"
+      LOCK_ERRORS+=("$w"); continue
+    fi
+    if [[ -z "$ins" ]]; then
+      bad "$w" "not installed"; note "declared $dec -> run npm install"
+      SDK_DRIFT+=("$w"); continue
+    fi
+    if [[ "$ins" != "$loc" ]]; then
+      bad "$w" "MISMATCH"
+      note "declared $dec | lockfile $loc | installed $ins"
+      note "out-of-range install from another branch -> npm ci"
+      SDK_DRIFT+=("$w")
+    else
+      ok "$w  $ins"
+    fi
+  done
+
+  printf '\n%s[2/4]%s built dist freshness (apps alias dist, not src)\n' "$YEL" "$OFF"
+  for p in "${DIST_PACKAGES[@]}"; do
+    [[ -d "$p" ]] || continue
+    local why
+    why="$(dist_staleness "$p")"
+    if [[ -n "$why" ]]; then
+      bad "$p/dist" "STALE"; note "$why"
+      STALE+=("$p")
+    else
+      ok "$p/dist"
+    fi
+  done
+
+  ISSUES=$(( ${#SDK_DRIFT[@]} + ${#LOCK_ERRORS[@]} + ${#STALE[@]} ))
+}
+
+scan
+FOUND=$ISSUES
+
+if [[ "$ISSUES" -eq 0 ]]; then
+  printf '\n%s[3/4]%s rebuild: not needed\n' "$YEL" "$OFF"
+  printf '%s[4/4]%s vite caches: left alone\n' "$YEL" "$OFF"
+  printf '\n%sPREFLIGHT OK%s  browser harnesses are safe to smoke\n\n' "$GRN" "$OFF"
+  exit 0
+fi
+
+if [[ "$CHECK_ONLY" -eq 1 ]]; then
+  printf '\n%s[3/4]%s rebuild: skipped (--check)\n' "$YEL" "$OFF"
+  printf '%s[4/4]%s vite caches: skipped (--check)\n' "$YEL" "$OFF"
+  printf '\n%sPREFLIGHT FAILED%s  %d issue(s); re-run without --check to fix\n\n' "$RED" "$OFF" "$FOUND"
+  exit 1
+fi
+
+if [[ ${#SDK_DRIFT[@]} -eq 0 && ${#STALE[@]} -eq 0 ]]; then
+  printf '\n%s[3/4]%s rebuild: skipped (lockfile pin missing; npm ci cannot create it)\n' "$YEL" "$OFF"
+  printf '%s[4/4]%s vite caches: left alone\n' "$YEL" "$OFF"
+  printf '\n%sPREFLIGHT FAILED%s  %d issue(s); add the missing lockfile pin(s) then re-run\n\n' "$RED" "$OFF" "$FOUND"
+  exit 1
+fi
+
+printf '\n%s[3/4]%s fixing\n' "$YEL" "$OFF"
+FIX_FAILED=0
+
+for w in ${SDK_DRIFT[@]+"${SDK_DRIFT[@]}"}; do
+  printf '  npm ci  %s ... ' "$w"
+  if (cd "$w" && npm ci >/dev/null 2>&1); then
+    echo "${GRN}ok${OFF}"
+    # A reinstall invalidates anything already built here.
+    for p in "${DIST_PACKAGES[@]}"; do
+      [[ "$p" == "$w" ]] && { case " ${STALE[*]+${STALE[*]}} " in *" $p "*) ;; *) STALE+=("$p");; esac; }
+    done
+  else
+    echo "${RED}FAILED${OFF}"; FIX_FAILED=1
+  fi
+done
+
+for p in ${STALE[@]+"${STALE[@]}"}; do
+  # clean, not a bare build: export names change across protocol lines, and tsc
+  # leaves orphaned files from the previous build behind.
+  printf '  clean+build %s ... ' "$p"
+  if (cd "$p" && npm run clean >/dev/null 2>&1 && npm run build >/dev/null 2>&1); then
+    echo "${GRN}ok${OFF}"
+  else
+    echo "${RED}FAILED${OFF}"; FIX_FAILED=1
+  fi
+done
+
+printf '\n%s[4/4]%s clearing vite dep caches\n' "$YEL" "$OFF"
+shopt -s nullglob
+for c in examples/*/node_modules/.vite examples/_shared/*/node_modules/.vite; do
+  rm -rf "$c" && printf '  removed %s\n' "$c"
+done
+shopt -u nullglob
+
+printf '\n%sre-verifying%s\n' "$DIM" "$OFF"
+scan
+
+if [[ "$ISSUES" -eq 0 && "$FIX_FAILED" -eq 0 ]]; then
+  printf '\n%sPREFLIGHT FIXED%s  %d issue(s) resolved\n' "$GRN" "$OFF" "$FOUND"
+  printf '%sRestart any running vite dev server so it picks up the rebuilt dist.%s\n\n' "$DIM" "$OFF"
+  exit 0
+fi
+
+printf '\n%sPREFLIGHT FAILED%s  %d issue(s) remain after fix\n\n' "$RED" "$OFF" "$ISSUES"
+exit 1