diff --git a/.github/workflows/sso-audit.yml b/.github/workflows/sso-audit.yml
new file mode 100644
index 0000000000..e19d519268
--- /dev/null
+++ b/.github/workflows/sso-audit.yml
@@ -0,0 +1,70 @@
+name: SSO fork audit
+
+# Runs scripts/sso-audit.sh against this fork's auth code to verify
+# satisfaction of the cross-app SSO contract at
+# awais786/sso-rules-moneta:openspec/specs/proxy-auth-middleware/spec.md.
+#
+# Covers fork-side rows 14, 20, 21 from SKILL.md §5. Exits 1 on security-
+# critical violations (row 20 — architectural immunity pinned by the
+# precedence regression-guard test).
+
+on:
+  pull_request:
+    paths:
+      - 'surfsense_backend/app/middleware/proxy_auth.py'
+      - 'surfsense_backend/app/users.py'
+      - 'surfsense_backend/tests/unit/test_current_active_user_proxy_precedence.py'
+      - 'surfsense_web/lib/auth-utils.ts'
+      - 'scripts/sso-audit.sh'
+      - '.github/workflows/sso-audit.yml'
+  push:
+    branches: [foss-main]
+  schedule:
+    - cron: '0 9 * * 1'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  sso-fork-audit:
+    runs-on: ubuntu-latest
+    # Grant `pull-requests: write` only to the sticky-comment step,
+    # not to the whole workflow. The audit step needs only `contents: read`.
+    permissions:
+      contents: read
+      pull-requests: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Run fork audit
+        id: audit
+        run: |
+          set -o pipefail
+          if bash scripts/sso-audit.sh | tee audit-output.md; then
+            echo "audit_exit=0" >> "$GITHUB_OUTPUT"
+          else
+            echo "audit_exit=$?" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Publish to job summary
+        if: always()
+        run: cat audit-output.md >> "$GITHUB_STEP_SUMMARY"
+
+      - name: Post sticky PR comment
+        if: |
+          github.event_name == 'pull_request' &&
+          github.event.pull_request.head.repo.full_name == github.repository &&
+          always()
+        continue-on-error: true
+        uses: marocchino/sticky-pull-request-comment@v2
+        with:
+          header: sso-fork-audit
+          path: audit-output.md
+
+      - name: Fail on security-critical violations
+        if: steps.audit.outputs.audit_exit != '0'
+        run: |
+          echo "::error::Security-critical SSO contract violation in fork audit. See table for the failing row and fix."
+          exit 1
diff --git a/scripts/sso-audit.sh b/scripts/sso-audit.sh
new file mode 100755
index 0000000000..81a83597da
--- /dev/null
+++ b/scripts/sso-audit.sh
@@ -0,0 +1,192 @@
+#!/usr/bin/env bash
+#
+# sso-audit.sh — SurfSense-side fork audit against the cross-app SSO contract.
+#
+# ============================================================================
+# Covers fork-side rows of awais786/sso-rules-moneta:openspec/specs/
+# proxy-auth-middleware/spec.md. SurfSense is architecturally immune to
+# the cross-user stale-session class of bug because current_active_user
+# resolves request.state.proxy_user (set per-request by ProxyAuthMiddleware
+# from X-Auth-Request-Email) BEFORE falling back to the JWT bearer
+# identity. The other four forks need an explicit Rule-2 flush; SurfSense
+# inherits the property from its precedence rule.
+#
+# This audit pins that precedence as a regression guard: the contract
+# holds if-and-only-if the precedence is unchanged, so we check for the
+# regression-guard test file added in Pressingly/SurfSense#22.
+#
+# Exit codes:
+#   0 — all rows ✅ or n/a / informational
+#   1 — at least one SECURITY-CRITICAL row failed
+#
+# Rows covered:
+#   Row 14 — logout shape: SPA logout (surfsense_web/lib/auth-utils.ts)
+#            MUST NOT call /oauth2/sign_out.
+#   Row 20 — session-identity reconciliation: SurfSense relies on
+#            `current_active_user` returning proxy_user before jwt_user
+#            (architectural immunity). The regression-guard test file
+#            MUST exist and pin the precedence. SECURITY-CRITICAL only
+#            if the test is missing (means no guard against future
+#            refactor flipping the precedence).
+#   Row 21 — email-shape detection MUST NOT use polynomial-backtracking
+#            regex. SurfSense uses `"@" not in email` substring check.
+# ============================================================================
+
+set -euo pipefail
+
+MIDDLEWARE="surfsense_backend/app/middleware/proxy_auth.py"
+USERS_PY="surfsense_backend/app/users.py"
+PRECEDENCE_TEST="surfsense_backend/tests/unit/test_current_active_user_proxy_precedence.py"
+AUTH_UTILS="surfsense_web/lib/auth-utils.ts"
+
+declare -a ROW_STATUS=()
+declare -a ROW_TITLES=(
+  "logout shape: SPA logout does not call /oauth2/sign_out"
+  "session-identity reconciliation: proxy>jwt precedence pinned by test"
+  "email-shape detection uses substring, not polynomial regex"
+)
+declare -a ROW_NOTES=()
+declare -a ROW_NUMBERS=(14 20 21)
+
+SECURITY_CRITICAL=(1)
+SECURITY_CRITICAL_FAILS=0
+
+record() {
+  local idx=$1 status=$2 note=$3
+  ROW_STATUS[$idx]="$status"
+  ROW_NOTES[$idx]="$note"
+  if [[ "$status" == "❌" ]]; then
+    for c in "${SECURITY_CRITICAL[@]}"; do
+      if [[ "$c" -eq "$idx" ]]; then
+        SECURITY_CRITICAL_FAILS=$((SECURITY_CRITICAL_FAILS + 1))
+        return
+      fi
+    done
+  fi
+}
+
+# ============================================================================
+# Row 14 (idx 0): logout shape — narrow check
+# ============================================================================
+check_row_14() {
+  if [[ ! -f "$AUTH_UTILS" ]]; then
+    record 0 "?" "$AUTH_UTILS not found — skipping"
+    return
+  fi
+
+  if grep -qE '/oauth2/sign_?out' "$AUTH_UTILS"; then
+    local line
+    line=$(grep -nE '/oauth2/sign_?out' "$AUTH_UTILS" | head -1)
+    record 0 "❌" "Logout calls \`/oauth2/sign_out\` at $AUTH_UTILS:$line — per logout-flow spec, per-app Logout is navigation-only. Drop the call; portal 'Logout all' handles oauth2-proxy clearing."
+    return
+  fi
+
+  record 0 "✅" "$AUTH_UTILS does not invoke \`/oauth2/sign_out\` (this row verifies only that the SPA doesn't try to clear the upstream proxy cookie itself; that's the portal's job)"
+}
+
+# ============================================================================
+# Row 20 (idx 1): session-identity reconciliation via architectural immunity
+#
+# SurfSense doesn't need an explicit Rule 2 flush because
+# `current_active_user` in app/users.py resolves:
+#   proxy_user (per-request from X-Auth-Request-Email) BEFORE jwt_user
+#
+# That precedence IS the contract. If a future refactor flips the
+# precedence or removes the proxy_user check, the cross-user stale-session
+# leak appears.
+#
+# We check two things:
+#   1. The precedence test file exists (regression guard pin).
+#   2. app/users.py still has the precedence pattern:
+#      proxy_user check returns FIRST, jwt_user fallback SECOND.
+#
+# SECURITY-CRITICAL: missing test = no guard against precedence-flip
+# regression. Reference: Pressingly/SurfSense#22.
+# ============================================================================
+check_row_20() {
+  if [[ ! -f "$USERS_PY" ]]; then
+    record 1 "?" "$USERS_PY not found — skipping"
+    return
+  fi
+
+  # The precedence pattern: in current_active_user, proxy_user is checked
+  # and returned BEFORE jwt_user. We grep for the canonical shape that
+  # makes the precedence visible.
+  local has_precedence
+  has_precedence=$(grep -cE "proxy_user.*is not None|return proxy_user" "$USERS_PY" || true)
+
+  local has_test
+  has_test=0
+  [[ -f "$PRECEDENCE_TEST" ]] && has_test=1
+
+  if [[ "$has_precedence" -gt 0 && "$has_test" -eq 1 ]]; then
+    record 1 "✅" "$USERS_PY preserves proxy_user > jwt_user precedence (architectural immunity); regression guard test at $PRECEDENCE_TEST pins the contract"
+    return
+  fi
+
+  if [[ "$has_precedence" -eq 0 ]]; then
+    record 1 "❌" "$USERS_PY does NOT show the proxy_user precedence pattern. SurfSense's immunity to the cross-user stale-session leak depends on \`current_active_user\` returning \`proxy_user\` before falling back to \`jwt_user\`. If this property is gone, the leak class is re-introduced. Reference: openspec proxy-auth-middleware §'Identity mismatch SHALL flush', surfsense-security.md §'architecturally immune', Pressingly/SurfSense#22."
+    return
+  fi
+
+  record 1 "❌" "$PRECEDENCE_TEST does NOT exist. The proxy_user > jwt_user precedence in $USERS_PY is the load-bearing reason SurfSense is immune to the cross-user stale-session leak — but it's unguarded by tests. A future refactor that flips the precedence (or removes the proxy_user check during a 'simplify auth' pass) would silently re-introduce the bug. Add the regression-guard test from Pressingly/SurfSense#22."
+}
+
+# ============================================================================
+# Row 21 (idx 2): polynomial-regex avoidance in email-shape detection
+# ============================================================================
+check_row_21() {
+  if [[ ! -f "$MIDDLEWARE" ]]; then
+    record 2 "?" "$MIDDLEWARE not found — skipping"
+    return
+  fi
+
+  local hits
+  hits=$(grep -nE '\^\[\^[\\\\]s@\]\+@\[\^[\\\\]s@\]\+\\\.\[\^[\\\\]s@\]\+\$' "$MIDDLEWARE" 2>/dev/null || true)
+
+  if [[ -n "$hits" ]]; then
+    record 2 "❌" "Polynomial-backtracking email-shape regex detected in $MIDDLEWARE: $hits. SurfSense uses a substring check (\`'@' not in email\`); introducing the explicit ^...$ regex form re-enables polynomial backtracking on adversarial input. Rewrite to substring or indexOf-based check per openspec proxy-auth-middleware §'email-shape detection SHALL avoid polynomial-backtracking regex'."
+    return
+  fi
+
+  record 2 "✅" "No polynomial-backtracking email-shape regex in $MIDDLEWARE; using substring check"
+}
+
+# ============================================================================
+# Run checks
+# ============================================================================
+check_row_14
+check_row_20
+check_row_21
+
+# ============================================================================
+# Print table
+# ============================================================================
+echo "## SurfSense SSO Fork Audit"
+echo
+echo "Cross-app contract: https://github.com/awais786/sso-rules-moneta/blob/main/openspec/specs/proxy-auth-middleware/spec.md"
+echo "Row numbers match the 21-row table at https://github.com/awais786/sso-rules-moneta/blob/main/skills/app-rules/SKILL.md#5-report"
+echo
+echo "| Row | Invariant | Status | Notes |"
+echo "|-----|-----------|--------|-------|"
+for i in "${!ROW_TITLES[@]}"; do
+  printf "| %d | %s | %s | %s |\n" \
+    "${ROW_NUMBERS[$i]}" "${ROW_TITLES[$i]}" "${ROW_STATUS[$i]:-?}" "${ROW_NOTES[$i]:-}"
+done
+echo
+
+TOTAL_FAILS=0
+for s in "${ROW_STATUS[@]}"; do
+  [[ "$s" == "❌" ]] && TOTAL_FAILS=$((TOTAL_FAILS + 1))
+done
+
+if [[ "$TOTAL_FAILS" -eq 0 ]]; then
+  echo "**All fork-side invariants hold.**"
+  exit 0
+fi
+
+echo "**$TOTAL_FAILS violations.** Security-critical (row 20): $SECURITY_CRITICAL_FAILS."
+if [[ "$SECURITY_CRITICAL_FAILS" -gt 0 ]]; then
+  exit 1
+fi
+exit 0