diff --git a/.vortex/installer/tests/Fixtures/handler_process/_baseline/AGENTS.md b/.vortex/installer/tests/Fixtures/handler_process/_baseline/AGENTS.md
index b32df8396..59c1c92a2 100644
--- a/.vortex/installer/tests/Fixtures/handler_process/_baseline/AGENTS.md
+++ b/.vortex/installer/tests/Fixtures/handler_process/_baseline/AGENTS.md
@@ -77,6 +77,7 @@ ahoy test-bdd -- --tags=@tagname  # Run Behat tests with specific tag
 
 - **Never modify** `scripts/vortex/` - use `scripts/custom/` for your scripts
 - **Never use** `ahoy drush php:eval` - use `ahoy drush php:script` instead
+- **Never pass inline code to commands** via stdin, heredocs, or `/dev/stdin` - always write code to a temporary file first, then pass the file path to the command (e.g. `ahoy drush php:script path/to/fix.php`)
 - **Always export config** after admin UI changes: `ahoy drush cex`
 - **Never use compound Bash commands.** See the highest priority rule at the top.
 
diff --git a/.vortex/installer/tests/Fixtures/handler_process/hosting_acquia/AGENTS.md b/.vortex/installer/tests/Fixtures/handler_process/hosting_acquia/AGENTS.md
index bf8f6765d..52d09ccfa 100644
--- a/.vortex/installer/tests/Fixtures/handler_process/hosting_acquia/AGENTS.md
+++ b/.vortex/installer/tests/Fixtures/handler_process/hosting_acquia/AGENTS.md
@@ -1,4 +1,4 @@
-@@ -82,8 +82,8 @@
+@@ -83,8 +83,8 @@
  
  ## Key Directories
  
diff --git a/.vortex/installer/tests/Fixtures/handler_process/hosting_project_name___acquia/AGENTS.md b/.vortex/installer/tests/Fixtures/handler_process/hosting_project_name___acquia/AGENTS.md
index bf8f6765d..52d09ccfa 100644
--- a/.vortex/installer/tests/Fixtures/handler_process/hosting_project_name___acquia/AGENTS.md
+++ b/.vortex/installer/tests/Fixtures/handler_process/hosting_project_name___acquia/AGENTS.md
@@ -1,4 +1,4 @@
-@@ -82,8 +82,8 @@
+@@ -83,8 +83,8 @@
  
  ## Key Directories
  
diff --git a/AGENTS.md b/AGENTS.md
index 80d3ac594..f68fe5235 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -87,6 +87,7 @@ ahoy test-bdd -- --tags=@tagname  # Run Behat tests with specific tag
 
 - **Never modify** `scripts/vortex/` - use `scripts/custom/` for your scripts
 - **Never use** `ahoy drush php:eval` - use `ahoy drush php:script` instead
+- **Never pass inline code to commands** via stdin, heredocs, or `/dev/stdin` - always write code to a temporary file first, then pass the file path to the command (e.g. `ahoy drush php:script path/to/fix.php`)
 - **Always export config** after admin UI changes: `ahoy drush cex`
 - **Never use compound Bash commands.** See the highest priority rule at the top.