diff --git a/.github/workflows/sso-audit.yml b/.github/workflows/sso-audit.yml
new file mode 100644
index 00000000000..cd95b6c76bd
--- /dev/null
+++ b/.github/workflows/sso-audit.yml
@@ -0,0 +1,68 @@
+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).
+
+on:
+  pull_request:
+    paths:
+      - 'backend/src/app/http/auth_request.clj'
+      - 'backend/src/app/http/session.clj'
+      - 'frontend/src/app/main/data/auth.cljs'
+      - '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 00000000000..75c51359717
--- /dev/null
+++ b/scripts/sso-audit.sh
@@ -0,0 +1,192 @@
+#!/usr/bin/env bash
+#
+# sso-audit.sh — Penpot-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 that a deterministic bash check can verify
+# against Penpot's source tree. Catches regressions BEFORE they reach
+# foss-server-bundle-devstack.
+#
+# 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 (frontend/src/app/main/data/auth.cljs)
+#            MUST NOT call /oauth2/sign_out.
+#   Row 20 — session-identity reconciliation (Rule 2 mismatch flush):
+#            backend/src/app/http/auth_request.clj MUST call
+#            (session/delete-fn cfg) on unresolvable mismatch OR
+#            (create-session!) on resolvable mismatch (in-place re-key).
+#            Both satisfy the contract; presence of either is the deterministic
+#            signal that wrap-authz reconciles upstream identity vs session.
+#            SECURITY-CRITICAL.
+#   Row 21 — email-shape detection MUST NOT use polynomial-backtracking
+#            regex. Penpot uses valid-email? helper (regex) — this row only
+#            fires if the unanchored polynomial-backtrack shape is introduced.
+# ============================================================================
+
+set -euo pipefail
+
+AUTH_REQUEST="backend/src/app/http/auth_request.clj"
+AUTH_FRONTEND="frontend/src/app/main/data/auth.cljs"
+
+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 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 "$AUTH_FRONTEND" ]]; then
+    record 0 "?" "$AUTH_FRONTEND not found — skipping"
+    return
+  fi
+
+  if grep -qE '/oauth2/sign_?out' "$AUTH_FRONTEND"; then
+    local line
+    line=$(grep -nE '/oauth2/sign_?out' "$AUTH_FRONTEND" | head -1)
+    record 0 "❌" "Logout calls \`/oauth2/sign_out\` at $AUTH_FRONTEND:$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 "✅" "$AUTH_FRONTEND does not invoke \`/oauth2/sign_out\` (this row verifies only that the SPA doesn't try to clear the upstream proxy cookie itself; that's the portal's job)"
+}
+
+# ============================================================================
+# Row 20 (idx 1): session-identity reconciliation
+#
+# Penpot's flush mechanism has three paths per the spec:
+#   1. Resolvable + active mismatch  →  in-place re-key (create-session! on
+#      response with the new profile-id)
+#   2. Blocked / inactive incoming   →  403 + renewal guard prevents stale
+#      cookie extension
+#   3. Unresolvable upstream         →  drop in-flight session markers AND
+#      expire the browser cookie via (session/delete-fn cfg)
+#
+# All three paths must exist in wrap-authz for the contract to hold. The
+# deterministic signal is the presence of `session/delete-fn` (the
+# drop+expire path, unique to Pressingly/penpot#18) AND `create-session!`
+# (the re-key path) in auth_request.clj.
+#
+# If either marker is absent, the middleware is in an earlier state where
+# wrap-authz short-circuited on the session cookie without consulting the
+# upstream header — the cross-user stale-session leak.
+#
+# SECURITY-CRITICAL: without these, the stale-session leak returns.
+# ============================================================================
+check_row_20() {
+  if [[ ! -f "$AUTH_REQUEST" ]]; then
+    record 1 "?" "$AUTH_REQUEST not found — skipping"
+    return
+  fi
+
+  local has_delete_fn
+  has_delete_fn=$(grep -cE "session/delete-fn" "$AUTH_REQUEST" || true)
+
+  local has_create_session
+  has_create_session=$(grep -cE "create-session!" "$AUTH_REQUEST" || true)
+
+  if [[ "$has_delete_fn" -gt 0 && "$has_create_session" -gt 0 ]]; then
+    record 1 "✅" "$AUTH_REQUEST contains \`session/delete-fn\` (drop+expire path) AND \`create-session!\` (re-key path) — Rule 2 three-path mismatch flush in place"
+    return
+  fi
+
+  local missing=""
+  [[ "$has_delete_fn" -eq 0 ]] && missing="${missing} session/delete-fn (drop+expire path);"
+  [[ "$has_create_session" -eq 0 ]] && missing="${missing} create-session! (re-key path);"
+
+  record 1 "❌" "$AUTH_REQUEST is missing:$missing The cross-app spec (proxy-auth-middleware Rule 2) requires wrap-authz to reconcile the upstream X-Auth-Request-Email against the session profile-id. On resolvable + active mismatch: re-key by calling create-session! on the response with the new profile-id. On unresolvable upstream: dissoc the session markers AND call (session/delete-fn cfg) to expire the browser cookie. Without both paths, the stale-session-on-user-switch leak returns. Reference: Pressingly/penpot#18."
+}
+
+# ============================================================================
+# Row 21 (idx 2): polynomial-regex avoidance in email-shape detection
+#
+# Penpot's `valid-email?` helper uses a regex. The audit fires only if the
+# unanchored polynomial-backtrack shape (^[^\s@]+@[^\s@]+\.[^\s@]+$) is
+# introduced. The current `[^\s@]+@[^\s@]+\.[^\s@]+` pattern with the
+# `re-matches` Clojure function is anchored by re-matches (not by `^...$`)
+# and on a fixed-size input is not exploitable. The audit looks specifically
+# for the explicit anchored polynomial shape.
+# ============================================================================
+check_row_21() {
+  if [[ ! -f "$AUTH_REQUEST" ]]; then
+    record 2 "?" "$AUTH_REQUEST not found — skipping"
+    return
+  fi
+
+  # Anchored polynomial-backtracking email-shape regex (the literal one
+  # CodeQL flags). Clojure regexes use Java syntax.
+  local hits
+  hits=$(grep -nE '\^\[\^[\\\\]s@\]\+@\[\^[\\\\]s@\]\+\\\.\[\^[\\\\]s@\]\+\$' "$AUTH_REQUEST" 2>/dev/null || true)
+
+  if [[ -n "$hits" ]]; then
+    record 2 "❌" "Polynomial-backtracking email-shape regex detected in $AUTH_REQUEST: $hits. The current valid-email? uses re-matches which anchors implicitly; introducing the explicit ^...$ form re-enables polynomial backtracking on adversarial input. Rewrite to substring-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 $AUTH_REQUEST; using re-matches (implicit anchoring on fixed-size input) or substring check"
+}
+
+# ============================================================================
+# Run checks
+# ============================================================================
+check_row_14
+check_row_20
+check_row_21
+
+# ============================================================================
+# Print table
+# ============================================================================
+echo "## Penpot SSO Fork Audit"
+echo
+echo "Cross-app contract: https://github.com/awais786/sso-rules-moneta/blob/main/openspec/specs/proxy-auth-middleware/spec.md"
+echo "Row numbers match the 21-row table at https://github.com/awais786/sso-rules-moneta/blob/main/skills/app-rules/SKILL.md#5-report"
+echo
+echo "| Row | Invariant | Status | Notes |"
+echo "|-----|-----------|--------|-------|"
+for i in "${!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