diff --git a/.github/workflows/sso-audit.yml b/.github/workflows/sso-audit.yml
new file mode 100644
index 0000000000000..f29c9a1dc2be3
--- /dev/null
+++ b/.github/workflows/sso-audit.yml
@@ -0,0 +1,86 @@
+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 — session-identity reconciliation) so the
+# merge gate blocks the stale-session leak class of bug.
+#
+# When upstream sso-rules-moneta adds a new fork-side row, vendor the
+# updated check into scripts/sso-audit.sh and re-run this workflow.
+
+on:
+  pull_request:
+    paths:
+      - 'packages/twenty-server/src/engine/guards/**'
+      - 'packages/twenty-server/src/engine/core-modules/auth/**'
+      - 'packages/twenty-front/src/modules/auth/**'
+      - 'scripts/sso-audit.sh'
+      - '.github/workflows/sso-audit.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  sso-fork-audit:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - 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: Upload audit output
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: sso-fork-audit-output
+          path: audit-output.md
+          if-no-files-found: warn
+
+      - 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
+
+  sso-fork-audit-comment:
+    # Run comment updates only on same-repo PRs. Fork PR tokens are read-only
+    # and cannot write PR comments.
+    if: |
+      always() &&
+      github.event_name == 'pull_request' &&
+      github.event.pull_request.head.repo.full_name == github.repository
+    needs: sso-fork-audit
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: write
+    steps:
+      - name: Download audit output
+        uses: actions/download-artifact@v4
+        with:
+          name: sso-fork-audit-output
+          path: audit-results
+
+      - name: Post sticky PR comment
+        continue-on-error: true
+        uses: marocchino/sticky-pull-request-comment@v2
+        with:
+          header: sso-fork-audit
+          path: audit-results/audit-output.md
diff --git a/scripts/sso-audit.sh b/scripts/sso-audit.sh
new file mode 100755
index 0000000000000..4999207d7c5d3
--- /dev/null
+++ b/scripts/sso-audit.sh
@@ -0,0 +1,257 @@
+#!/usr/bin/env bash
+#
+# sso-audit.sh — Twenty-side fork audit against the cross-app SSO contract.
+#
+# ============================================================================
+# Covers the fork-side rows of awais786/sso-rules-moneta:openspec/specs/
+# proxy-auth-middleware/spec.md that a deterministic bash check can verify
+# against Twenty's source tree. Catches regressions BEFORE they reach
+# foss-server-bundle-devstack, where the same rows currently emit `?` (no
+# fork code on disk in the bundle CI).
+#
+# Together with the bundle-side audit and the per-fork audits in Plane /
+# Outline / Penpot / SurfSense, the cross-app contract is now ~14 of 21
+# rows deterministic without any LLM invocation.
+#
+# Exit codes:
+#   0 — all rows ✅ or n/a / informational
+#   1 — at least one SECURITY-CRITICAL row failed (today: row 20 session-
+#       identity reconciliation). These violations re-open the cross-user
+#       identity-leak class of bug.
+#
+# Rows covered:
+#   Row 14 — logout shape: SPA logout file (packages/twenty-front/src/
+#            modules/auth/hooks/useAuth.ts) MUST NOT call /oauth2/sign_out.
+#            (The portal-host redirect target uses buildPortalUrl — verified
+#            elsewhere; this row only enforces no /oauth2/sign_out literal.)
+#   Row 20 — session-identity reconciliation (Rule 2 mismatch flush):
+#            JwtAuthGuard MUST call response.clearCookie('tokenPair', ...)
+#            on identity mismatch when AUTH_TYPE === 'SSO'. Without this,
+#            the stale-session-on-user-switch leak returns.  SECURITY-CRITICAL.
+#   Row 21 — email-shape detection MUST NOT use polynomial-backtracking
+#            regex. Twenty uses indexOf-based detection in
+#            normalizeProxyEmail today; this row fires only if a regex is
+#            reintroduced.
+#
+# Source of truth: awais786/sso-rules-moneta:openspec/specs/proxy-auth-
+# middleware/spec.md. When upstream adds a new fork-side row, vendor the
+# updated check here.
+# ============================================================================
+
+set -euo pipefail
+
+JWT_GUARD="packages/twenty-server/src/engine/guards/jwt-auth.guard.ts"
+USE_AUTH="packages/twenty-front/src/modules/auth/hooks/useAuth.ts"
+# clearCookie('tokenPair', ...)
+CLEAR_COOKIE_PATTERN='clearCookie\(\s*['"'"'"]tokenPair['"'"'"]'
+# get('AUTH_TYPE') === 'SSO'
+AUTH_TYPE_SSO_PATTERN='get\(\s*['"'"'"]AUTH_TYPE['"'"'"]\s*\)\s*===\s*['"'"'"]SSO['"'"'"]'
+MISMATCH_HEADER_PATTERN="X-Auth-Request-Email"
+MISMATCH_USER_PATTERN="data\\.user\\.email"
+# 25 lines keeps the required signals in one logical guard block while
+# tolerating normal formatting/wrapping drift.
+PROXIMITY_WINDOW=25
+
+declare -a ROW_STATUS=()
+declare -a ROW_TITLES=(
+  "logout shape: SPA logout does not call /oauth2/sign_out"
+  "session-identity reconciliation present (Rule 2 mismatch flush)"
+  "email-shape detection uses indexOf, not polynomial regex"
+)
+declare -a ROW_NOTES=()
+declare -a ROW_NUMBERS=(14 20 21)
+
+# Security-critical row indices (0-indexed into ROW_NUMBERS above).
+SECURITY_CRITICAL=(1)   # index 1 → row 20
+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
+#
+# SPA logout MUST NOT contain `/oauth2/sign_out` literal. Twenty's logout
+# uses `buildPortalUrl` to compute the redirect target; this audit only
+# verifies the SPA doesn't try to clear the upstream proxy cookie itself.
+# ============================================================================
+check_row_14() {
+  if [[ ! -f "$USE_AUTH" ]]; then
+    record 0 "?" "$USE_AUTH not found — skipping"
+    return
+  fi
+
+  if grep -qE '/oauth2/sign_?out' "$USE_AUTH"; then
+    local line
+    line=$(grep -nE '/oauth2/sign_?out' "$USE_AUTH" | head -1)
+    record 0 "❌" "Logout calls \`/oauth2/sign_out\` at $USE_AUTH:$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 "✅" "$USE_AUTH does not invoke \`/oauth2/sign_out\` (this row verifies only that the SPA doesn't try to clear the upstream proxy cookie itself; that's the portal's job)"
+}
+
+# ============================================================================
+# Row 20 (idx 1): session-identity reconciliation
+#
+# JwtAuthGuard MUST clear the tokenPair cookie on identity mismatch:
+#   response.clearCookie('tokenPair', { path: '/' })
+#
+# AND it MUST gate the mismatch check on AUTH_TYPE === 'SSO' so non-SSO
+# deployments are unaffected.
+#
+# Deterministic signal:
+#   - SSO gate: get('AUTH_TYPE') === 'SSO'
+#   - mismatch operands: X-Auth-Request-Email + data.user.email
+#   - token flush: clearCookie('tokenPair', ...)
+# All must exist in the same nearby block (within ±PROXIMITY_WINDOW lines), so unrelated
+# AUTH_TYPE/clearCookie references elsewhere in the file cannot false-pass.
+#
+# SECURITY-CRITICAL: without this, the stale-session leak returns.
+# ============================================================================
+check_row_20() {
+  if [[ ! -f "$JWT_GUARD" ]]; then
+    record 1 "?" "$JWT_GUARD not found — skipping"
+    return
+  fi
+
+  local clear_cookie_lines
+  clear_cookie_lines=$(grep -nE "$CLEAR_COOKIE_PATTERN" "$JWT_GUARD" || true)
+
+  local auth_type_lines
+  auth_type_lines=$(grep -nE "$AUTH_TYPE_SSO_PATTERN" "$JWT_GUARD" || true)
+
+  local mismatch_header_lines
+  mismatch_header_lines=$(grep -nE "$MISMATCH_HEADER_PATTERN" "$JWT_GUARD" || true)
+
+  local mismatch_user_lines
+  mismatch_user_lines=$(grep -nE "$MISMATCH_USER_PATTERN" "$JWT_GUARD" || true)
+
+  if [[ -n "$clear_cookie_lines" && -n "$auth_type_lines" && -n "$mismatch_header_lines" && -n "$mismatch_user_lines" ]]; then
+    local nearby_match
+    nearby_match=$(
+      awk \
+        -v clearPattern="$CLEAR_COOKIE_PATTERN" \
+        -v authPattern="$AUTH_TYPE_SSO_PATTERN" \
+        -v headerPattern="$MISMATCH_HEADER_PATTERN" \
+        -v userPattern="$MISMATCH_USER_PATTERN" \
+        -v window="$PROXIMITY_WINDOW" '
+        $0 ~ clearPattern { clear[NR]=1 }
+        $0 ~ authPattern { auth[NR]=1 }
+        $0 ~ headerPattern { header[NR]=1 }
+        $0 ~ userPattern { user[NR]=1 }
+        END {
+          for (line = 1; line <= NR; line++) {
+            hasClear = 0
+            hasAuth = 0
+            hasHeader = 0
+            hasUser = 0
+            for (i = line - window; i <= line + window; i++) {
+              if (clear[i]) hasClear = 1
+              if (auth[i]) hasAuth = 1
+              if (header[i]) hasHeader = 1
+              if (user[i]) hasUser = 1
+            }
+            if (hasClear && hasAuth && hasHeader && hasUser) {
+              print 1
+              exit
+            }
+          }
+          print 0
+        }
+      ' "$JWT_GUARD"
+    )
+
+    if [[ "$nearby_match" == "1" ]]; then
+      record 1 "✅" "$JWT_GUARD contains nearby SSO gate + identity-mismatch comparison + \`clearCookie('tokenPair'\` (within ±$PROXIMITY_WINDOW lines) — Rule 2 mismatch flush in place"
+      return
+    fi
+  fi
+
+  if [[ -z "$clear_cookie_lines" ]]; then
+    record 1 "❌" "$JWT_GUARD does NOT call \`response.clearCookie('tokenPair', ...)\`. The cross-app spec (proxy-auth-middleware Rule 2) requires the guard to clear the tokenPair cookie when oauth2-proxy asserts a different identity than the JWT user. Without it, the stale-session-on-user-switch leak returns. Fix: add a comparison of \`X-Auth-Request-Email\` vs \`data.user.email\` after \`validateTokenByRequest\`, and on mismatch call \`response.clearCookie('tokenPair', { path: '/' })\` then return false. Gate the check on \`AUTH_TYPE === 'SSO'\`."
+    return
+  fi
+
+  record 1 "❌" "$JWT_GUARD has \`clearCookie('tokenPair'\` but missing a nearby full Rule 2 block: \`get('AUTH_TYPE') === 'SSO'\` + \`X-Auth-Request-Email\` vs \`data.user.email\` comparison in the same conditional path. Keep these checks colocated to avoid false passes from unrelated references."
+}
+
+# ============================================================================
+# Row 21 (idx 2): polynomial-regex avoidance in email-shape detection
+#
+# Twenty uses indexOf-based detection in normalizeProxyEmail (added in
+# Pressingly/twenty#8). This is a regression guard — fires only if a
+# polynomial-backtracking regex like /^[^\s@]+@[^\s@]+\.[^\s@]+$/ is
+# reintroduced. CodeQL's `js/polynomial-redos` flags it on adversarial input.
+# ============================================================================
+check_row_21() {
+  if [[ ! -f "$JWT_GUARD" ]]; then
+    record 2 "?" "$JWT_GUARD not found — skipping"
+    return
+  fi
+
+  # Look for the canonical polynomial-backtracking shape used in JS regex
+  # literals: /^[^\s@]+@[^\s@]+\.[^\s@]+$/ and variations.
+  local hits
+  hits=$(grep -nE '\[\^[\\\\]s@\]\+@\[\^[\\\\]s@\]\+\\\.\[\^[\\\\]s@\]\+' "$JWT_GUARD" 2>/dev/null || true)
+
+  if [[ -n "$hits" ]]; then
+    record 2 "❌" "Polynomial-backtracking email-shape regex detected in $JWT_GUARD: $hits. Rewrite to indexOf-based check per openspec proxy-auth-middleware §'email-shape detection SHALL avoid polynomial-backtracking regex'. Reference: \`normalizeProxyEmail\` in this file."
+    return
+  fi
+
+  record 2 "✅" "No polynomial-backtracking email-shape regex in $JWT_GUARD; using indexOf-based detection"
+}
+
+# ============================================================================
+# Run checks
+# ============================================================================
+check_row_14
+check_row_20
+check_row_21
+
+# ============================================================================
+# Print table
+# ============================================================================
+echo "## Twenty SSO Fork Audit"
+echo
+echo "Cross-app contract: https://github.com/awais786/sso-rules-moneta/blob/main/openspec/specs/proxy-auth-middleware/spec.md"
+echo "Row numbers match the 21-row table at https://github.com/awais786/sso-rules-moneta/blob/main/skills/app-rules/SKILL.md#5-report"
+echo
+echo "| Row | Invariant | Status | Notes |"
+echo "|-----|-----------|--------|-------|"
+for i in "${!ROW_TITLES[@]}"; do
+  printf "| %d | %s | %s | %s |\n" \
+    "${ROW_NUMBERS[$i]}" "${ROW_TITLES[$i]}" "${ROW_STATUS[$i]:-?}" "${ROW_NOTES[$i]:-}"
+done
+echo
+
+# ============================================================================
+# Summary + exit code
+# ============================================================================
+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