fix: Keep README.md redirect targets, update validator to handle them

GitBook resolves README.md in redirect targets as directory URLs, so
these don't need to be changed. Update the validator to accept
foo/README.md when foo.md exists as the page file.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: louis-pre

.gitbook.yaml

@@ -16,8 +16,8 @@ redirects:
   core-concepts/workspaces/personal-access-tokens: core-concepts/authentication/personal-access-tokens.md
   core-concepts/workspaces/client-session-tokens: core-concepts/authentication/client-session-tokens/README.md
   core-concepts/workspaces/client-session-tokens/implementing-client-sessions-for-device-management-in-the-backend: core-concepts/authentication/client-session-tokens/implementing-client-sessions-for-device-management-in-the-backend.md
-  products/access-systems/user-management: capability-guides/access-systems/user-management.md
-  capability-guides/access-systems/managing-credentials: capability-guides/access-systems/managing-credentials.md
+  products/access-systems/user-management: capability-guides/access-systems/user-management/README.md
+  capability-guides/access-systems/managing-credentials: capability-guides/access-systems/managing-credentials/README.md
   capability-guides/access-systems/assigning-credentials-to-users: capability-guides/access-systems/managing-credentials/assigning-credentials-to-users.md
   products/access-systems/suspending-and-unsuspending-users: capability-guides/access-systems/user-management/suspending-and-unsuspending-users.md
   products/seam-bridge-in-development: capability-guides/seam-bridge.md

codegen/validate-redirects.ts

@@ -46,6 +46,12 @@ function pageExists(fullPath: string): boolean {
   if (existsSync(join(fullPath, 'README.md'))) return true
   // URL-style target without .md extension (e.g., api/devices → api/devices.md)
   if (!fullPath.endsWith('.md') && existsSync(fullPath + '.md')) return true
+  // README.md targets resolve as directory URLs in GitBook, so check if the
+  // parent path resolves as a page (e.g., foo/README.md → foo.md).
+  if (fullPath.endsWith('/README.md')) {
+    const parentPath = fullPath.slice(0, -'/README.md'.length)
+    if (existsSync(parentPath + '.md')) return true
+  }
   return false
 }