sim: return removed chunk hashes from remove_shard_dedup_entries

[sirahd]

Summary

DeletionControlableClient::remove_shard_dedup_entries previously returned Result<()>, discarding which global-dedup keys it reclaimed. The production CAS gc_delete_shard_dedup endpoint already returns the removed chunk hashes; this brings the simulation clients in line so callers (GC Stage 4's dedup-removal audit) can observe the same data through the simulation harness.

Changes

• Trait (deletion_controls.rs): remove_shard_dedup_entries(&self, shard_hash) -> Result<Vec<MerkleHash>>.
• LocalClient: accumulates the GLOBAL_DEDUP_TABLE keys it deletes (across the retry passes) and returns them.
• MemoryClient: collects global_dedup keys before clear() (the in-memory client holds a single shard, so all entries belong to it).
• HTTP path: the local-server route serializes the list as Json(Vec<HexMerkleHash>); SimulationControlClient parses it back into Vec<MerkleHash>.
• Tests: the shared test_remove_shard_dedup_entries_* cases now assert the returned list reports the target shard's chunks and excludes other shards'; the no-op case asserts an empty list. The SimulationControlClient suite + the builder-wired server test cover the full HTTP serialize→parse round-trip.

Motivation / downstream

Consumed by xet-garbage-collection Stage 4, which collects removed chunk hashes into an audit artifact (GC PR #102). That PR's SimulationConnector currently returns an empty list because this trait didn't surface it; once this lands and GC bumps its pinned xet-core rev, the simulation path can carry the real chunk list end-to-end.

Testing

• cargo build -p xet-client --features simulation — clean.
• cargo test -p xet-client --features simulation deletion — 7 passed (LocalClient, memory backend, and SimulationControlClient HTTP suite).
• cargo clippy -r -p xet-client --features simulation -- -D warnings — clean. (Pre-existing --all-targets test-code lints in hub_client/client.rs and chunk_cache/disk.rs are untouched here.)

🤖 Generated with Claude Code

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Note

Low Risk
Changes are confined to the simulation feature and deletion-control APIs; behavior for unknown shards remains a no-op with an empty list, with expanded test coverage.

Overview
remove_shard_dedup_entries now returns Vec<MerkleHash> of reclaimed global-dedup chunk keys, aligned with production gc_delete_shard_dedup, so GC simulation can audit deregistered dedup entries.

The DeletionControlableClient trait and all simulation backends (LocalClient, MemoryClient) collect and return the keys they delete. The local-server DELETE /simulation/shards/{hash}/dedup_entries route responds with Json(Vec<HexMerkleHash>) instead of an empty body; SimulationControlClient deserializes that list. Shared deletion tests and the builder-wired HTTP test assert the returned set matches the target shard and is empty for unknown shards.

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