Template 19: document readiness checks and reprovisioning criteria for older deployments

Problem

A freshly provisioned Template 19 environment can work while an older Foundry Agent Service deployment with apparently similar networking still fails private MCP DNS or connectivity. The current guidance does not provide a compact way to determine whether the older resource is equivalent to the current reference pattern or must be recreated.

Suggested improvement

Add an "existing deployment readiness and migration" section that shows how to verify:

• Standard Agent Setup/capability host health;
• networkInjections[].scenario == agent;
• useMicrosoftManagedNetwork == false for BYO VNet;
• delegated agent subnet and service association link health;
• private DNS zone linkage and resolution;
• whether network injection was configured at initial account creation; and
• which configuration differences require reprovisioning rather than an in-place fix.

Please distinguish these outcomes:

1. deployment matches the current pattern and should be troubleshot in place;
2. DNS/subnet/capability-host configuration can be repaired;
3. network injection cannot be added or changed in place and the account must be recreated.

Why this helps

It prevents a successful clean-room test from turning into a blanket "recreate everything" recommendation, while still making the true reprovisioning cases explicit.

Start by locating the current Template 19 guidance and compare it with the existing deployment checks listed in the issue. Add an existing-deployment readiness and migration section that distinguishes in-place troubleshooting, repairable configuration, and cases requiring account recreation.