sandbox:read-only (macOS Seatbelt)
-- reasoning --
I'm scanning the pull request code for bugs. I notice the metrics ordering seems swapped between the counter labels and their pushed values, and the sweep sorting logic looks like it removes the newest blobs instead of the oldest despite the comment saying otherwise.

Continuing through: the admin route calls the sweeper synchronously, bypassing the mutex meant to prevent concurrent runs and blocking the async executor with a synchronous filesystem walk. Worse, the dry-run path still unconditionally calls forget on the index, meaning a "dry run" actually deletes index entries — a serious bug. I also flag that the config uses unstable Duration constructor APIs like from_hours and from_mins, which may not compile on stable Rust.

Partials aren't counted toward remaining bytes. I also need to check store.rs to see if blob filenames match the full hex digest or are sharded — if index keys don't align with actual filenames, contains_key checks could fail systematically and delete everything every sweep. And mtime-based aging is suspect: if cache hits don't refresh mtime, the comment claiming recently-accessed files survive is simply wrong, which is a real doc/logic mismatch worth flagging.
I'll start by reading the new sweep module and its neighbours in the repo.
└ 1528 tok ·  72.3 tok/s · 19K ctx · 4145ms ttft · 21.1s wall
↳ glob_files: glob services/proxy/src/**/*.rs in pr
└ glob_files: glob complete
↳ read_file: read pr/services/proxy/src/sweep.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/store.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/metrics.rs
└ read_file: read complete
auto-compress is on at 85% but the context window of "anthropic/claude-opus-5" on openrouter is unknown, so this run will not compress - set AFI_SOURCE_OPENROUTER_CONTEXT_WINDOW (or pass --context-window) to enable it
-- reasoning --
I'm spotting a real bug in the metrics ordering — the COUNTERS constant lists blobs_removed then bytes_reclaimed, but the values() function returns them swapped. Then I catch another defect in the sweep logic: candidates are sorted by ascending age, which actually puts the newest blobs first despite the comment claiming "oldest first" — meaning sweep is removing the wrong blobs entirely.

I also check the byte-threshold comparison and decide the `>=` check is basically fine. Then I trace a potential race condition where a blob might get swept between being committed and having its index link written, so I go look at cache.rs to see the actual ordering of those operations. Finally I catch what looks like a serious defect: forget() is called unconditionally even in dry-run mode, meaning dry runs are actually deleting index entries for blobs that were never removed.

Then I find another defect: clear_partials doesn't apply any age check to in-progress temp files, so a sweep can unlink a file mid-download—the writer keeps writing to the unlinked inode, but the later rename to commit the file fails with ENOENT, causing the fetch to error out. This is a real bug since the partials path lacks the min_age protection that the blob path has, so I'm now checking how admin::sweep invokes the sweeper.

The admin sweep handler also calls the sweeper's dry_run directly, bypassing the running mutex, so an admin-triggered sweep can run concurrently with the background one despite the module's one-at-a-time claim. Worse, both paths execute the blocking synchronous walk without spawn_blocking—run() does it inside a tokio::spawn task and the admin handler does it inside an async function—so either can block a runtime worker thread for a long time, which is worth flagging as a performance issue given they intentionally excluded it from the ten-second timeout.

Checking that admin::sweep does call authorise, and the route is POST outside the timeout, both fine. I'm also noting that cache_min_age isn't validated, though a zero value should be harmless, and I'm trying to recall whether Duration::from_mins/from_hours are stable in the Rust version being targeted or still gated behind the duration_constructors feature.

Since from_days and from_weeks are still unstable, this could fail to compile on older toolchains, so I want to check the rust-version in Cargo.toml. I'm tracing through the sweep logic: held is computed correctly from candidates, remaining decrements properly for both held and unreferenced blob removals, and index entries are collected via a metadata-reading candidate builder that looks fine. I'm also confirming that when a referenced blob exceeds the ceiling and meets the min_age threshold, it gets removed and its index entry forgotten correctly, though I want to check whether the "gone" set might incorrectly include a hex name from an unreferenced blob.

Since that name wouldn't be a valid digest hex anyway, it seems fine. I also want to check the race condition with cache serving, specifically the commit/link ordering in cache.rs, and confirm that remaining's comparison to max_bytes only accounts for blob directory bytes, ignoring index file sizes, and that dry_run partial clearing counts files without properly gating on dry_run. Now I should go read through routes/admin.rs, routes/mod.rs, routes/cache.rs, config.rs, main.rs, and Cargo.toml.
Now the routes, config, and main to check the sweep's callers.
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↳ read_file: read pr/services/proxy/src/routes/admin.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/routes/mod.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/routes/cache.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/config.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/main.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/Cargo.toml
└ read_file: read complete
-- reasoning --
I'm cataloging bugs: the metrics values() function returns counters in swapped order from how COUNTERS labels them, mislabeling stats. Then in sweep.rs, sorting by age ascending actually evicts newest blobs first despite the comment claiming oldest-first eviction.

There's also an off-by-one where `remaining >= max_bytes` triggers eviction right at the ceiling rather than past it, and a more serious race condition: a blob committed during an in-flight fetch but not yet linked to the registry could be swept as unreferenced, causing a later request to fail with a 500 when it tries to reopen a blob that's already been deleted.

I'm also spotting that clear_partials wipes files in `incoming` without checking age, which could delete the temp file of an active in-progress download — the writer would keep writing to a now-missing fd, and the rename on commit would fail with ENOENT, causing a mid-download 500. The doc comment's claim that files in `incoming` are always abandoned fetches doesn't hold up, since link() also uses temp files in that same directory that could get caught by the sweep.

More critically, dry_run mode still populates and deletes the `gone` index entries — so a "dry run" that promises not to remove anything actually deletes index files, which is a serious correctness bug worth flagging as high/critical.

I'm also noting that sweep is a synchronous, potentially long-running filesystem walk called directly from an async route handler and from the background task without spawn_blocking, which blocks the executor thread for the whole walk — a real performance/availability issue worth reporting separately.

Then I'm seeing that the admin route calls sweeper.sweep() directly instead of going through run(), bypassing the mutex that's supposed to serialize sweeps, so concurrent admin and background sweeps can overlap despite the module's documented "one at a time" guarantee — since reclaim is synchronous it can't await the lock, so a try_lock approach might be the fix. I'm also checking whether the route ordering between the per-digest DELETE and the sweep POST could conflict given how axum's router merges static and parameterized paths.

Also worth noting: no validation that cache_max_bytes exceeds max_artifact_bytes, which could cause thrashing, but that's minor. More concerning is whether `Duration::from_hours`/`from_mins` are even stable in the Rust version being targeted — I recall these constructors were unstable for a while under a feature flag before being stabilized, so I need to check which Rust version this assumes.

Also the sweep's `held` count only tracks blobs, ignoring index/incoming for the ceiling comparison, which is minor. The eviction condition combined with newest-first sorting confirms it evicts hottest data first, same as the earlier bug I flagged. And there's a subtler issue: blobs with unreadable mtimes default to age 0, making them look newest and thus protected from ceiling-based removal — low severity, probably not worth flagging strongly.

Then there's a more serious symlink issue: `collect`'s recursion follows symlinked directories since fs::metadata resolves symlinks, so a symlink to root inside the blob dir would make sweep traverse the whole filesystem and delete unreferenced files anywhere. The code comment claiming links are counted at their own size is actually false — it reports the target's size and unlinks the symlink itself, so the comment contradicts the real behavior; this should use symlink_metadata instead. Worth flagging as a medium-severity issue at sweep.rs:164.

I also check a few smaller things: the index sweep's use of `collect` for computing sizes/ages is fine, `forget`'s removal of index entries handles shared digests correctly, and unreferenced blob removal happening regardless of ceiling appears intentional. The metrics call ordering matches its signature, and in main.rs the sweep task's panic behavior is a low-severity concern since a panicking spawned task would silently stop future sweeps.

Now I'm compiling the final severity list: the dry_run flag incorrectly deleting index entries, the metrics values being swapped, and the sort order causing eviction of the wrong blobs are all critical (🔴) issues, while the query parameter parsing quirk with `dry_run` and the silent sweep task panic are minor concerns worth noting but lower priority.

Moving down, I'm flagging orange-level issues: clear_partials deleting in-flight temp files, a race between unreferenced-blob removal and commit-before-link, and a blocking synchronous walk running on the async runtime. I'm also working out exactly which line to cite for the mutex bypass versus the blocking call, since they land on the same call site in admin.rs and sweep.rs — I'll attribute the lock bypass to admin.rs:76 and the blocking concern to a nearby line in sweep.rs.

Below that, at yellow severity, I'm noting the same sync filesystem walk issue is triggered by two different callers, plus symlink-following behavior during sweep. At blue severity I've spotted an off-by-one where a blob gets removed exactly when it hits the size ceiling, and I'm second-guessing whether the dry-run partial count is actually a real issue or just noise — it looks trivial. I'm also cross-checking sweep's documented behavior ("clears partial writes left by dead fetches") against the in-flight deletion bug, and noting that store's "held" reporting is worth a second look too.

The real critical finding: dry-run mode still deletes index entries unconditionally — `forget` calls `fs::remove_file` for every marked candidate regardless of the dry_run flag, meaning a "preview" sweep actually causes cache misses for everything it claims it would remove. Worse, that also creates a cascading effect where subsequent real sweeps see those now-unreferenced blobs and delete them for real. I'm also flagging that the sweep endpoint just returns 200 with JSON regardless, and that there's no validation ensuring cache_min_age is greater than zero in the config.

I've confirmed sweep_interval and cache_max_bytes are properly validated, min_age of zero is semantically fine, and the .env.example value of 34359738368 correctly matches 32 GiB. Now I'm pulling together exact line references for the writeup — the cache.rs race sits between the commit at line 151 and the link at line 163, the clear_partials removal call is at line 232, and the metrics counters are ordered across lines 51-57 with their values at 94-95.
I have everything I need. Findings below, each tied to the line I read.

🔴 `bug` services/proxy/src/sweep.rs:140: `forget` runs unconditionally, so `POST /v1/admin/cache/sweep?dry_run=true` deletes every index entry naming a blob it merely *reported* — `gone` is populated at line 137 regardless of `dry_run`. The advertised "reports what one would reclaim without removing anything" (docs/operations.md) silently un-caches the store, and the next real sweep then deletes those now-unreferenced blobs.

🔴 `bug` services/proxy/src/metrics.rs:94: `values()` returns bytes-reclaimed where `COUNTERS[4]` is `cairn_proxy_sweep_blobs_removed_total` and blobs-removed where `COUNTERS[5]` is `cairn_proxy_sweep_bytes_reclaimed_total`; the two sweep counters are exposed under each other's names, so the alert docs/operations.md tells operators to build on `cairn_proxy_sweep_bytes_reclaimed_total` reads a blob count. Swap lines 94 and 95.

🔴 `bug` services/proxy/src/sweep.rs:102: `sort_by_key(|c| c.age)` orders *ascending* age — newest first — so the over-ceiling loop evicts the blobs most recently fetched, exactly the opposite of the comment on line 100 and of the `CACHE_MIN_AGE` grace period's purpose (a fresh blob just past `min_age` goes before a year-old one). Sort by `std::cmp::Reverse(candidate.age)`.

🟠 `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* temp files of `BlobStore::writer` (store.rs:201) and of `BlobStore::link` (store.rs:147). A sweep firing during a 200 MiB download deletes the file under the open handle, and `BlobWriter::commit`'s rename (store.rs:259) fails with ENOENT, turning a healthy fetch into a 500. Only files older than `min_age` (or than `fetch_timeout`) are abandoned.

🟠 `bug` services/proxy/src/sweep.rs:119: the "nothing points at it" branch ignores age, but a freshly committed blob is unreferenced for the whole of the registry round trip — cache.rs commits at line 151 and only calls `store.link` at line 163. A sweep in that window removes the blob, and the reopen at cache.rs:90 fails with "a blob committed by this request is already missing from the store". Unreferenced blobs must also be older than `min_age` before they are removed.

🟠 `performance` services/proxy/src/sweep.rs:90: `sweep` is a synchronous full-tree `read_dir`/`metadata`/`unlink` walk, and both callers run it directly on a runtime worker — `Sweeper::run` at line 84 and the handler at routes/admin.rs:76. On the large store the module doc contemplates this parks a worker thread for the whole walk, stalling the async tasks (including in-flight artifact streams) scheduled on it. It needs `tokio::task::spawn_blocking`.

🟡 `bug` services/proxy/src/routes/admin.rs:76: the route calls `sweeper.sweep(...)` and not `sweeper.run()`, bypassing the `running` mutex (sweep.rs:67) that the module doc at sweep.rs:10 says makes one-sweep-at-a-time a property of the type. Two concurrent `POST /v1/admin/cache/sweep` calls, or one racing the background tick, each size their removals against a total the other is shrinking and take the store far under the ceiling.

🟡 `bug` services/proxy/src/sweep.rs:164: `fs::metadata` follows symlinks, contradicting the comment on lines 160-163 — a symlink is counted at its *target's* size, and a symlinked directory inside the blob dir makes `collect` recurse outside the store, where its files are then unreferenced and unlinked at line 126. Use `fs::symlink_metadata` and skip non-regular files.

🔵 `bug` services/proxy/src/sweep.rs:120: `remaining >= self.max_bytes` removes one more blob when the store is exactly at the ceiling; the ceiling is documented as the most the store *may* hold, so this should be `>`.
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