diff --git a/docs/plans/2026-08-04-authz-permissions-implementation.md b/docs/plans/2026-08-04-authz-permissions-implementation.md
index 2b2a58d9..10c01502 100644
--- a/docs/plans/2026-08-04-authz-permissions-implementation.md
+++ b/docs/plans/2026-08-04-authz-permissions-implementation.md
@@ -2031,6 +2031,8 @@ interface RequestAuthz {
   resolver: AuthzResolver;
   /** Memo for object resources, keyed by identity so two rows never collide. */
   byRef: WeakMap<object, Map<string, Promise<AuthorizationDecision>>>;
+  /** Memo for symbol resources, which also carry identity. */
+  bySymbol: Map<symbol, Map<string, Promise<AuthorizationDecision>>>;
   /** Memo for primitive and absent resources. */
   byValue: Map<string, Promise<AuthorizationDecision>>;
 }
@@ -2062,6 +2064,7 @@ export function authzMiddleware(options: AuthzResolverOptions): Middleware {
     ctx.locals[AUTHZ_LOCALS_KEY] = {
       resolver,
       byRef: new WeakMap(),
+      bySymbol: new Map(),
       byValue: new Map(),
     } satisfies RequestAuthz;
     return next();
@@ -2076,8 +2079,16 @@ export function decideFor(
   const request = readAuthz(ctx);
   const scope = currentScope(ctx);
   // Scope is part of the key: the same permission decides differently per tenant.
-  // JSON-encoded so a tenant id containing the separator cannot collide.
-  const key = JSON.stringify([scope?.tenantId ?? "", permission]);
+  // Subject and scope are both part of the key. A request that reassigns
+  // ctx.user (impersonation, step-up auth, session revocation) or ctx.tenant
+  // must not be served the previous principal's verdict from the memo.
+  const subjectId = (ctx.user as { id?: unknown } | null | undefined)?.id;
+  const key = JSON.stringify([
+    scope?.tenantId ?? "",
+    permission,
+    typeof subjectId,
+    String(subjectId),
+  ]);
 
   const run = () =>
     request.resolver.decide({
@@ -2090,6 +2101,19 @@ export function decideFor(
   // Object resources memo by IDENTITY. Serialising them would let two distinct
   // rows share a key and cross-authorize, and unserialisable ones (circular
   // refs, BigInt fields, throwing getters) would all collapse into one bucket.
+  // Symbols carry identity that String() erases, so they memo by identity too.
+  // They are held in a plain Map rather than the WeakMap: the memo is discarded
+  // with the request, so there is nothing to leak.
+  if (typeof resource === "symbol") {
+    let perSymbol = request.bySymbol.get(resource);
+    if (!perSymbol) request.bySymbol.set(resource, (perSymbol = new Map()));
+    const cached = perSymbol.get(key);
+    if (cached) return cached;
+    const pending = run();
+    perSymbol.set(key, pending);
+    return pending;
+  }
+
   if (resource !== null && (typeof resource === "object" || typeof resource === "function")) {
     let perResource = request.byRef.get(resource as object);
     if (!perResource) request.byRef.set(resource as object, (perResource = new Map()));
@@ -2100,8 +2124,10 @@ export function decideFor(
     return pending;
   }
 
-  // typeof is part of the key so 7 and "7" are not the same resource.
-  const valueKey = JSON.stringify([key, typeof resource, String(resource)]);
+  // typeof is part of the key so 7 and "7" are not the same resource, and
+  // -0 keeps its sign because String(-0) is "0".
+  const rendered = Object.is(resource, -0) ? "-0" : String(resource);
+  const valueKey = JSON.stringify([key, typeof resource, rendered]);
   const cached = request.byValue.get(valueKey);
   if (cached) return cached;
   const pending = run();
@@ -2161,13 +2187,20 @@ export function guardPermission(permission: string, options: GuardOptions = {}):
 
     if (options.redirectTo && !wantsJson(ctx)) {
       if (!isLocalPath(options.redirectTo)) {
+        // JSON-encode: this branch exists precisely for values containing
+        // CR/LF, which would otherwise forge a second log line.
         console.error(
-          `[wrnexus:authz] redirectTo must be a local path, got '${options.redirectTo}'; denying`,
+          `[wrnexus:authz] redirectTo must be a local path, got ${JSON.stringify(options.redirectTo)}; denying`,
         );
       } else {
         return new Response(null, {
           status: 303,
-          headers: { location: options.redirectTo, "cache-control": "private, no-store" },
+          headers: {
+            // Header values must be Latin-1; a localized path like /accounts
+            // in non-ASCII would otherwise throw and 500 on a denial path.
+            location: encodeURI(options.redirectTo),
+            "cache-control": "private, no-store",
+          },
         });
       }
     }