The strongest case for keeping
A detail that seems incidental today may later explain a failure, vindicate someone, or reveal a promise. The person deciding what to discard can be mistaken or self-serving. An advocate of broad preservation can reasonably keep a large archive while retrieving only a small, relevant portion.
What can be lost in either direction
Imagine a brief objection recorded before a project failed. At the time it seemed unhelpful. Later it might show that someone recognized the risk and was ignored. Deleting it because the current account looked tidier would make that account harder to challenge.
Now consider a private confidence with no continuing reason for retention, or information that was placed in the wrong person's record. Future usefulness cannot simply be assumed to override the reasons for limiting access or retention.
Neither example yields one rule for every record. They show why purpose, permissions, recoverability, and the consequences of deletion need explicit consideration. The uncertainty cuts both ways.
Pause here: Are we deciding whether to retain this record, who may see it, or whether it belongs in this encounter?
Retention needs its own policy
The Memory design preserves authoritative capsules without rewriting their original constitution. Separate admission and portfolio rules address what enters a particular encounter. Omitting a record from the prompt does not necessarily delete it.
That distinction makes a large archive compatible with bounded attention. The design provisions cited here do not, however, establish a complete policy for indefinite retention, deletion, or recovery.
An immutability rule concerns whether a retained authoritative record may be rewritten. It does not, by itself, establish that every record must exist forever. Nor does a limited prompt justify silently discarding the material it leaves out. Each decision needs the right authority and an honest account of what would be lost.
My answer: A memory system should preserve useful, permitted history under an explicit retention policy. Keeping everything forever is a serious proposal with benefits and costs, not a consequence automatically supplied by immutability or by selective retrieval.