{"answer":"Read the sweep module, its callers, the store it walks, and the config/metrics wiring. Findings:\n\n🔴 `bug` services/proxy/src/sweep.rs:140: `forget(&index, &gone)` runs unconditionally, and `gone` is filled at line 137 even when `dry_run` is true — so `POST /v1/admin/cache/sweep?dry_run=true` deletes every index entry naming a blob the sweep *would* have removed (`fs::remove_file(path)` at line 252 has no dry-run guard). The route documented as \"reports what one would reclaim without removing anything\" (docs/operations.md, admin.rs:87) silently unlinks the name index, turning the next build's hits into a full refetch storm against upstreams.\n\n🔴 `bug` services/proxy/src/sweep.rs:232: `clear_partials` unlinks *every* file in `incoming` with no age or liveness test, but that directory holds the in-flight temporary of each running fetch (`BlobStore::temp_path`, store.rs:204) and of each index write (store.rs:147). A sweep — automatic every `CAIRN_SWEEP_INTERVAL`, 15m by default — deletes the temp of a download that is proceeding fine; the writer's `fs::rename(&temp, &target)` at store.rs:259 then fails with ENOENT and the client gets a 500 on a perfectly good artifact. The doc comment's premise (\"a fetch that is not coming back\") is untrue for anything currently streaming.\n\n🟠 `bug` services/proxy/src/sweep.rs:102: `sort_by_key(|candidate| candidate.age)` sorts *ascending*, i.e. newest first, the opposite of the comment above it and of the eviction policy documented in config.rs:63. Combined with the `age >= min_age` gate at line 120, the sweep removes the youngest blobs that have just cleared the grace period and keeps the oldest, so the cache evicts exactly what a pipeline is still using. Needs `sort_by_key(|c| std::cmp::Reverse(c.age))`.\n\n🟠 `bug` services/proxy/src/metrics.rs:94: `values()` returns `sweep_bytes_reclaimed` in slot 4 and `sweep_blobs_removed` in slot 5, but `COUNTERS` (lines 50-57) names slot 4 `cairn_proxy_sweep_blobs_removed_total` and slot 5 `..._bytes_reclaimed_total`. The two sweep counters are exported under each other's names, so the metric docs/operations.md tells operators to alert on reports a blob count, not bytes. Swap the two loads.\n\n🟠 `performance` services/proxy/src/routes/admin.rs:76: `reclaim` calls the synchronous `Sweeper::sweep` directly on the runtime thread, as does `Sweeper::run` at sweep.rs:84 inside the spawned task. The module doc (sweep.rs:14-18) deliberately uses blocking `std::fs`, and routes/mod.rs:125 admits a sweep \"legitimately takes longer than ten seconds\" — that is a tokio worker blocked for the whole walk, stalling every download futures scheduled on it. Both call sites need `tokio::task::spawn_blocking`.\n\n🟠 `bug` services/proxy/src/routes/admin.rs:76: the HTTP route bypasses the `running` mutex by calling `sweep()` instead of `run()`, so the \"one sweep at a time\" invariant the lock exists to keep (sweep.rs:10-12, 65-67) does not hold for the on-demand route. Two concurrent admin sweeps, or one racing the interval sweep, each compute `remaining` from a total the other is already shrinking and together take the store far below the ceiling.\n\n🟡 `bug` services/proxy/src/sweep.rs:119: an unreferenced blob is removed with no grace period at all, but a miss commits the blob (cache.rs:151) before it writes the index entry (cache.rs:163) — during that window nothing points at it. A sweep landing there deletes the blob the request just stored; if it lands between the commit and `open_blob` (cache.rs:90) the request fails with the \"already missing from the store\" 500. The unreferenced branch should still respect `min_age`.\n\n🟡 `bug` services/proxy/src/sweep.rs:164: `fs::metadata` follows symlinks, contradicting the comment directly above it (a symlink is counted at its target's size, not the link's) and, worse, making `collect` recurse into symlinked directories — a link pointing at an ancestor inside `CAIRN_BLOB_DIR` recurses until the stack overflows. Use `fs::symlink_metadata`.\n\n🔵 `bug` services/proxy/src/sweep.rs:134: a failed `fs::remove_file` at line 126 only logs, then falls through to count the blob in `removed`/`bytes` and push it into `gone`. Space that was never reclaimed is reported to the operator and added to `cairn_proxy_sweep_bytes_reclaimed_total`, and its index entries are dropped though the blob is still there — `clear_partials` gets this right with its `continue` at line 234.\n\n🔵 `bug` services/proxy/src/sweep.rs:120: `remaining >= self.max_bytes` evicts when the store is exactly at the ceiling, though `cache_max_bytes` is documented as \"the most the blob store may hold\" (config.rs:63); should be `>`.","auth":{"mode":"api_key"},"effort":"high","elapsed_secs":142.229,"error":null,"error_kind":null,"instructions":[],"model":"anthropic/claude-opus-5","ok":true,"sandbox":{"backend":"macOS Seatbelt","denied_read_roots":["/Users/bart.smykla@konghq.com/Projects/github.com/smykla-skalski/benchee/subjects"],"environment":["HOME","LANG","LC_ALL","PATH","TERM","TMPDIR"],"mode":"read-only","network":"denied","protected_write_roots":["/private/var/folders/d1/tvmyp5cs1gz38rltf390ddpw0000gn/T/benchee-agent-4E6g9b/.git","/private/var/folders/d1/tvmyp5cs1gz38rltf390ddpw0000gn/T/benchee-agent-4E6g9b/.afi","/private/var/folders/d1/tvmyp5cs1gz38rltf390ddpw0000gn/T/benchee-agent-4E6g9b/.agents","/private/var/folders/d1/tvmyp5cs1gz38rltf390ddpw0000gn/T/benchee-agent-4E6g9b/.codex","/private/var/folders/d1/tvmyp5cs1gz38rltf390ddpw0000gn/T/benchee-agent-4E6g9b/AGENTS.md","/private/var/folders/d1/tvmyp5cs1gz38rltf390ddpw0000gn/T/benchee-agent-4E6g9b/CLAUDE.md"],"readable_paths":["/"],"readable_roots":["/private/var/folders/d1/tvmyp5cs1gz38rltf390ddpw0000gn/T/benchee-agent-4E6g9b","/bin","/sbin","/usr/bin","/usr/sbin","/usr/lib","/usr/libexec","/usr/share","/System/Library","/Library/Apple","/Library/Filesystems/NetFSPlugins","/Library/Preferences","/private/etc","/private/var/db/timezone","/private/var/db/DarwinDirectory/local/recordStore.data","/private/var/select/developer_dir","/private/var/select/sh","/opt/homebrew/bin","/opt/homebrew/Cellar","/opt/homebrew/etc/gitconfig","/opt/homebrew/lib","/opt/homebrew/opt","/usr/local/bin","/Applications/Xcode.app/Contents/Developer","/Applications/Xcode.app/Contents","/Users/bart.smykla@konghq.com/.local/bin/afi"],"writable_roots":["/private/var/folders/d1/tvmyp5cs1gz38rltf390ddpw0000gn/T/afi-sandbox-gxltNI"]},"schema_version":1,"source":"openrouter","sources":[{"auth":{"mode":"api_key"},"source":"openrouter","usage":{"cache_read_tokens":0,"cache_write_tokens":0,"cost_usd":0.795385,"estimated_tokens":0,"input_tokens":105232,"output_tokens":2427,"reasoning_tokens":8342,"requests":3,"total_tokens":116001}}],"system_prompt":{"file":null,"mode":"builtin"},"tools":["read_file","write_file","edit_file","list_dir","search_files","glob_files","run_bash","wait_background"],"usage":{"budget":{"converged":false,"hard_ratio":0.95,"limit_usd":12.0,"soft_ratio":0.8,"spent_usd":0.795385,"stopped":false},"cache_read_tokens":0,"cache_write_tokens":0,"cost_usd":0.795385,"estimated_tokens":0,"input_tokens":105232,"output_tokens":2427,"reasoning_tokens":8342,"refused_by_approval":0,"refused_by_policy":0,"refused_tool_calls":0,"requests":3,"total_tokens":116001}}