Read the V8 limit and used heap together for initial admission, checkpoint
decode and remaining result capacity. Remove the duplicated second heap/RSS
observation while preserving every reserve and ceiling.
Make the controlled parent-capacity fixture internally consistent and test
both unchanged usage and a later one-MiB collection. Real worker/transfer
coverage still retains static/module facts and declines only the large graph.
Assisted-by: Reimu (gensokyo-skills:reimu-incident-triage)
Assisted-by: Kogasa (gensokyo-skills:kogasa-surprise-testing)