DEVX-109: docs: add container-level fix verification and verified state modification rules

AGENTS.md

@@ -522,6 +522,33 @@ create-task: devx-create-task
 - Secrets are passed via environment variables, never on the command line
 - All user-facing strings wrapped in `_()` for i18n
 
+### Container-Level Fix Verification (Mandatory)
+
+**Rule:** Before pushing any fix that modifies container state (CA certs,
+config files, installed packages, daemon restarts), reproduce the exact
+sequence locally with the actual Docker image. Do not push to CI as the
+first test.
+
+This is a hard rule, not a suggestion. CI cycles take 20+ minutes and
+ephemeral staging VMs are destroyed after each run, making interactive
+debugging impossible. A local reproduction takes 30 seconds and catches
+silent failures immediately.
+
+**Procedure:**
+1. `docker pull <actual_image>`
+2. `docker run -d --name <test> ...` and wait for it to start
+3. Run the exact commands from the Ansible task or script
+4. Verify the state change took effect
+5. Clean up: `docker rm -f <test>`
+
+### Verified State Modification (Mandatory)
+
+Ansible tasks that modify container state with `changed_when: false`
+MUST include a post-task verification step that confirms the state
+change took effect. `changed_when: false` suppresses both change
+detection AND failure visibility — a task can silently do nothing and
+report `ok`.
+
 ## Subagent Delegation Policy
 
 Custom subagent profiles are defined in `.devin/agents/` (project-specific)