Add explicit confirmation for local installation (#14897)

Enhance the local installation warning to require typing 'yes' to
proceed, making risks impossible to miss. Users following external
tutorials often don't see the documentation warning until after
their server is already modified.

Changes:
- Replace press-ENTER prompt with explicit 'yes' confirmation
- List specific consequences (firewall, DNS, no uninstall)
- Add local_install_confirmed variable for automation
- Document skip method in deploy-to-ubuntu.md

Closes #14362

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

docs/deploy-to-ubuntu.md

@@ -21,6 +21,17 @@ For local installation on the same machine, you must run:
 sudo ./algo
 ```
 
+## Confirmation Prompt
+
+Local installation displays a warning and requires you to type `yes` to proceed. This ensures you understand that Algo will modify firewall rules and system settings, and that there is no uninstall option.
+
+For automated deployments or CI/CD pipelines, skip the confirmation with:
+```bash
+ansible-playbook main.yml -e "provider=local local_install_confirmed=true server=localhost endpoint=YOUR_IP"
+```
+
+Only use `local_install_confirmed=true` when you have already taken a backup and understand the risks.
+
 ## Road Warrior Setup
 
 A "road warrior" setup lets you securely access your home network and its resources when traveling. This involves installing Algo on a server within your home LAN.

roles/local/tasks/prompts.yml

@@ -1,14 +1,43 @@
 ---
-- pause:
+- name: Display local installation warning
+  pause:
     prompt: |
-      https://trailofbits.github.io/algo/deploy-to-ubuntu.html
 
-      Local installation might break your server. Use at your own risk.
+      ======================================================================
+                          *** DESTRUCTIVE OPERATION ***
+      ======================================================================
 
-      Proceed? Press ENTER to continue or CTRL+C and A to abort...
-  when: not tests|default(false)|bool
-  tags:
-    - skip_ansible_lint
+      Algo is designed for DEDICATED VPN servers only.
+
+      This installation will:
+        - Replace all firewall rules (blocks most incoming traffic)
+        - Modify system network and DNS settings
+        - Install and configure VPN services
+
+      THERE IS NO UNINSTALL OPTION.
+
+      If this server runs other services (web, database, mail, etc.),
+      they will likely become inaccessible.
+
+      Recommended: Take a snapshot/backup before proceeding.
+
+      Documentation: https://trailofbits.github.io/algo/deploy-to-ubuntu.html
+
+      ======================================================================
+
+      Type 'yes' to confirm you understand the risks and want to proceed:
+  register: _local_warning_confirm
+  when:
+    - not tests | default(false) | bool
+    - not local_install_confirmed | default(false) | bool
+
+- name: Abort if not confirmed
+  fail:
+    msg: "Installation aborted by user. Your server was not modified."
+  when:
+    - not tests | default(false) | bool
+    - not local_install_confirmed | default(false) | bool
+    - _local_warning_confirm.user_input | default('') | lower != 'yes'
 
 - pause:
     prompt: |