Qualify observed default container names without hiding configuration

[Pigbibi]

Changes

• Accept the observed provider default name only for an unnamed single container without dependency references.
• Record that qualified baseline mode and recheck it after staging.
• Preserve explicit names, all other configuration, old traffic, IAM and Scheduler checks.

Verification

• 55 targeted stage and workflow tests passed.
• Ruff, compilation and diff checks passed.
• Independent material review passed; real staging and cached read remain pending.