[MathisWellmann]

Introduces the new crate: symbiont-memory

Archive (archive.rs, render.rs):

• stores every evaluated attempt (source, finite Score, a report written for the model) up to a set capacity.
• When full, it evicts the worst entry, but never from a protected recent tail. Bad recent results therefore still warn the next lane.
• Memory::render shows the best attempts (the top ones with source) and the newest ones within a token budget.
• Recurring failures (failures.rs): reads EvolutionTraces and caught panics.
• Counts rustc error headlines once per lane. Free-standing numbers are normalized, so index 5 and index 7 count as one failure.
• Failures seen at least min_occurrences times render as "Known pitfalls", in the order they were first seen. A rising count therefore never reorders text that is already cached.

ACE playbook (playbook.rs):

• itemized lessons in ACE's format, [str-00003] helpful=X harmful=Y :: lesson (arXiv:2510.04618).
• Duplicates are found by word-set Jaccard overlap, so no embedding model is needed.
• A bullet is pruned when its harmful count exceeds its helpful count by prune_margin.
• When the playbook is full, its weakest bullet is dropped.
• By default, a new bullet must cite evidence, i.e. a measured attempt.
• Hosts can add lessons they already know through playbook_mut.

Reflection (reflection.rs)

• reflection_request builds one prompt from the attempts committed since the last review, covering each attempt's score against its parents, its report, its code, and the bullets that attempt's lane was shown.
• The host sends this prompt to any model, then passes the answer to apply_reflection.
• This combines ACE's Reflector and Curator into one call per round. Merge order is tags, then prune, then add.
• Each request has an id, so an answer applies at most once. If the answer contains no JSON, the request stays outstanding. abandon_reflection puts the attempts back in the queue after a failed model call.

Islands (island.rs):

• the classic counter to a population collapsing onto one program (FunSearch, OpenEvolve).
• Archive capacity is enforced per island.
• Playbook bullets have a Scope: global or one island.
• Rendered gets an island part between the shared part and the lane part.
• migrate moves each island's best attempts one hop around a ring. It also promotes island lessons whose net count reached promote_net to the global playbook.
• reset_island clears a stagnant island.
• novelty uses token-trigram Jaccard similarity, ignoring layout and comments, to reject near copies before an expensive evaluation.
• With the default single island, behaviour is unchanged. The only difference is the explicit IslandId argument.

Observability

• every state change emits a structured debug-level tracing event. Turn them on with RUST_LOG=symbiont_memory=debug. A traced_test checks the key events.
• Config for hosts: every config struct is #[serde(default)], so a RON/JSON file only needs the fields it changes. MemoryConfig::validate checks the limits again, because deserializing skips the checking constructors. Memory::new panics on an invalid config so the error shows up immediately, not later.
• When the host excludes ids it renders itself, the elite section is titled "Best attempts not shown above" instead of the wrong "Best attempts so far".