fix(distributed): preserve master protocol extensions

Carry prefix-cache pressure and reported residency over PostgreSQL, keep truthful backend stop replies, and retain capacity-aware S3 staging release over the worker control tunnel after the rebase.

Adapt the overlapping master tests to the tunnel-native protocol and cover cross-replica cache events and departed-node cleanup.

Assisted-by: Codex:GPT-5 [apply_patch] [exec_command]
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f