Enforce memory maintainer scans

[jackysp]

Summary

• pin the reserved memory maintainer to standard/chat, including preset reapplication
• bind maintainer memory calls to the input namespace
• require complete memory_list cursor traversal before mutations or a successful final response
• document the runtime contract and add regression coverage

Why

The deployed maintainer inherited the server default model and returned an unverified report without calling memory_list. Maintenance runs need host-enforced enumeration instead of relying on prompt compliance alone.

Impact

Existing compatible schedules keep their enabled state, namespace payload, and cron configuration when the preset is reapplied. Maintainer runs that skip enumeration, cross namespaces, omit a returned cursor, or mutate before completing the scan now fail.

Validation

• cargo test --workspace --all-targets — 52 passed, 1 ignored
• cargo clippy --workspace --all-targets -- -D warnings
• cargo fmt --all -- --check
• git diff --check

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