Write-time admission control for the knowledge store (#970). The cap +
importance-eviction is a backstop after the fact is written; admission is
the boundary before it, so a capped store fills with signal, not noise.
Applied only to direct ctx_knowledge remember (the agent-facing path);
internal restorers (archive rehydrate, cognition auto-promotion) bypass it.
[memory.compaction]: no effect. Cluster compaction (#971) ran only in the
retired cognition loop (DEPRECATIONS.toml config-memory-compaction); the
section stays accepted, unvalidated, so existing configs keep loading.
[memory.episodic]: no effect. The episode memory is retired
(DEPRECATIONS.toml config-memory-episodic-procedural); the section stays
accepted, unvalidated, so existing configs keep loading. Its
LEAN_CTX_EPISODIC_* environment variables are ignored.
[memory.procedural]: no effect. The procedure memory is retired
(DEPRECATIONS.toml config-memory-episodic-procedural); the section stays
accepted, unvalidated, so existing configs keep loading. Its
LEAN_CTX_PROCEDURAL_* environment variables are ignored.