0.2.46: security hardening (external-fund scope, role guards, forced password rotation, headers)

Pre-release audit fixes:
- External Administrators can only act on investors already in their own funds
  (grant_access, create_statement, set_partner_exited, import match), closing a
  cross-fund account-takeover chain.
- Role and is_active changes are gated: no self-escalation, non-approvers cannot
  mint or alter approver accounts, and the Service Admin is protected.
- must_change_password is enforced server-side, not just in the client.
- Session cookie is Secure with a 12h max-age and SameSite; CSP and standard
  security headers on every response; the app refuses to boot on a known or short
  session secret; uvicorn runs with proxy-headers so login throttling keys on the
  real client IP behind the platform proxy.
- Import preview no longer confirms cross-fund investors; no-store on document
  downloads.
- Adds backend/tests/test_security_hardening.py (15 tests); full suite 76 passing.
- SECURITY-AUDIT.md records the swarm audit, findings, and remediation status.

deploy/start.sh

@@ -1,16 +1,24 @@
 #!/bin/sh
 set -e
 
-# Generate session secret if not set or default
-if [ "$TEN31_SESSION_SECRET" = "change-me" ]; then
-  if [ -f /data/.session-secret ]; then
-    export TEN31_SESSION_SECRET=$(cat /data/.session-secret)
-  else
-    export TEN31_SESSION_SECRET=$(python3 -c "import secrets; print(secrets.token_hex(32))")
-    echo "$TEN31_SESSION_SECRET" > /data/.session-secret
-    chmod 600 /data/.session-secret
-  fi
-fi
+# Generate a session secret unless the operator supplied a real one. Any unset/empty value or a
+# known placeholder counts as "not set" — the app also refuses to boot on these (see
+# main.lifespan), so the two checks must agree on the full placeholder list.
+case "$TEN31_SESSION_SECRET" in
+  ""|change-me|change-me-in-production)
+    if [ -f /data/.session-secret ]; then
+      export TEN31_SESSION_SECRET=$(cat /data/.session-secret)
+    else
+      export TEN31_SESSION_SECRET=$(python3 -c "import secrets; print(secrets.token_hex(32))")
+      echo "$TEN31_SESSION_SECRET" > /data/.session-secret
+      chmod 600 /data/.session-secret
+    fi
+    ;;
+esac
+
+# The platform terminates TLS and reverse-proxies to us, so the session cookie is served over
+# HTTPS to the client: mark it Secure. Default on here; overridable for a plain-HTTP setup.
+export TEN31_SESSION_COOKIE_SECURE="${TEN31_SESSION_COOKIE_SECURE:-true}"
 
 # Create first approver on first boot if no users exist
 if [ ! -f /data/.initialized ]; then
@@ -58,10 +66,16 @@ LOG_LEVEL="${TEN31_LOG_LEVEL:-info}"
 # Hand off to the server as an unprivileged user. The platform mounts /data owned by root, so
 # (while still root) we take ownership of the data volume first, then drop privileges with
 # setpriv — the long-running server process is never root, limiting what a compromise can reach.
+# --proxy-headers lets uvicorn read X-Forwarded-For from the platform's reverse proxy so the
+# login rate limiter keys on the real client IP, not the single proxy address (otherwise one
+# source's failures throttle every user). The container port is only reachable via that proxy,
+# so trusting forwarded headers from any upstream is safe here.
 if [ "$(id -u)" = "0" ]; then
   chown -R 10001:10001 /data
   exec setpriv --reuid=10001 --regid=10001 --clear-groups \
-    uvicorn ten31portal.main:app --host 0.0.0.0 --port 8000 --log-level "$LOG_LEVEL"
+    uvicorn ten31portal.main:app --host 0.0.0.0 --port 8000 --log-level "$LOG_LEVEL" \
+    --proxy-headers --forwarded-allow-ips="*"
 else
-  exec uvicorn ten31portal.main:app --host 0.0.0.0 --port 8000 --log-level "$LOG_LEVEL"
+  exec uvicorn ten31portal.main:app --host 0.0.0.0 --port 8000 --log-level "$LOG_LEVEL" \
+    --proxy-headers --forwarded-allow-ips="*"
 fi