sandbox:read-only (macOS Seatbelt)
-- reasoning --
I'm reviewing the pr/ files for defects, and I'm noticing that the sweep route calls the sweeper synchronously and directly without acquiring the running mutex, which could let an on-demand sweep run concurrently with a background one, violating the "one sweep at a time" guarantee.

I'm also noticing the background loop's `run` method holds the mutex while executing a synchronous filesystem walk on the tokio runtime, blocking the async worker thread instead of using spawn_blocking — problematic given the docs acknowledge large sweeps can take over ten seconds.

Beyond that, `clear_partials` seems to remove all files in `incoming` indiscriminately, which could delete a temp file for a fetch that's actively being written rather than one that's genuinely abandoned; I want to check store.rs to confirm where the writer places its temp files and whether there's any age-based grace period before deletion.

For eviction, I'm also double-checking the sort order — the candidates are sorted by age ascending, which given how age is computed (larger age = older blob) would actually put the newest blobs first rather than oldest, meaning eviction may target the wrong candidates first.

Separately, I want to check the metrics array ordering against the values-list order, since a mismatch there would render byte counts under the wrong counter label and vice versa.

I also want to check whether `Duration::from_hours` and `from_mins` are actually stable in the Rust version being targeted, since I recall those constructors were gated behind the unstable `duration_constructors` feature and may not compile on stable.

More importantly, I'm noticing that the dry-run sweep logic still calls `forget` unconditionally on the index entries even when dry_run skips the actual file removal — meaning dry runs could still mutate the index despite being meant as a no-op preview.  That's a real bug since blobs never actually removed would lose their index entries, making them look unreferenced next sweep. I should flag this as a critical correctness issue tied to the `forget(&index, &gone)` call, needing to be gated behind `!dry_run`. I also note a smaller issue where `forget` removes entries even when the underlying file removal failed, which seems like a minor inconsistency worth mentioning separately.

I also spot that the reclaim route handler runs synchronously and calls into the sweeper directly, which would block the async runtime for potentially long directory walks and also skips the mutex protection — this is another concrete defect I want to flag at admin.rs. Finally, I notice a mismatch between a comment and the actual behavior around symlink handling: the code uses `fs::metadata`, which follows symlinks, contradicting a comment suggesting links are sized by the link itself rather than the target.

I need to check store.rs to see where partial writes go and how eviction interacts with naming and ordering — the eviction loop only triggers once remaining reaches the ceiling, and given the earlier candidate-ordering bug it may remove newest blobs instead of oldest, though the `held` accounting for blobs looks fine. The admin sweep route does check authorization, but it bypasses the sweep mutex entirely, so despite documentation claiming "one sweep at a time," concurrent manual and background sweeps can actually run simultaneously — confirming the defect noted earlier.
I'll read the key files in the PR to verify the sweep logic, store layout, and metrics.
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↳ read_file: read pr/services/proxy/src/sweep.rs
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↳ read_file: read pr/services/proxy/src/store.rs
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↳ read_file: read pr/services/proxy/src/metrics.rs
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↳ read_file: read pr/services/proxy/src/routes/admin.rs
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auto-compress is on at 85% but the context window of "anthropic/claude-fable-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 potential defect: the sweep in clear_partials removes all files in `incoming`, including partial writes from fetches currently in progress, since there's no minimum-age check. This means a temp file for an active fetch could get deleted mid-flight, even though the docstring implies files in `incoming` are abandoned fetches.

That would cause `BlobWriter::commit`'s rename to fail with ENOENT since the source was unlinked, so any fetch overlapping with a sweep would fail — a real race condition. I'm also flagging the eviction condition using `>=` instead of `>` for the max_bytes comparison, which seems like a minor off-by-one since holding exactly max_bytes should be allowed per the docs.

There's also a more serious race: since sweep reads the referenced index before collecting candidate blobs, a blob committed via rename right before its index link write would look unreferenced and get deleted regardless of age, since the code explicitly skips age-checking for unreferenced removal.  If that deleted blob then gets linked in the index anyway, later reads would resolve to a missing blob and need a refetch — a genuine TOCTOU bug worth flagging at line 119.

Separately, the sweeper runs synchronous std::fs operations directly on the async executor thread, both from `run()` and from the admin reclaim route handler, and should really be wrapped in `spawn_blocking` instead.

I also notice admin.rs:76 calls `sweeper.sweep(dry_run)` directly rather than through `run()`, which skips the `running` mutex entirely -- meaning concurrent admin sweeps or an admin sweep racing the background interval sweep can violate the module's "one sweep at a time" guarantee.

I'm also spotting a swapped indexing bug in metrics.rs: the values() function returns bytes reclaimed at index 4 and blobs removed at index 5, but COUNTERS lists them in the opposite order, so the exported metric names get attached to the wrong values -- exactly the failure mode the code comment warns about.

Then there's a more severe issue in sweep(): when dry_run is true, forget() is still called unconditionally on the "gone" set, actually deleting index entries via fs::remove_file even though the blob removal itself is properly gated behind dry_run. That means a dry run silently mutates the store, orphaning blobs that a subsequent real sweep will then delete regardless of their age -- a critical correctness bug.

There's also a secondary issue where if a blob's file removal fails for a reason other than NotFound, the code still treats it as removed and forgets its index entries anyway, which orphans a still-existing blob on disk and corrupts the byte-accounting.

I'm also questioning whether `Duration::from_hours`/`from_mins` in config.rs are actually stable Rust — I recall `duration_constructors` was still unstable/partially stabilized around 1.81-1.83, so I need to double check if these calls would even compile.

The eviction boundary check is minor. The bigger issue is that the sweep can delete in-flight partial files for active downloads — since large downloads can take minutes while sweeps run every 15 minutes, a concurrent fetch could have its temp file removed mid-transfer, causing the commit rename to fail and the fetch to error out. This looks like a genuine high-severity bug where sweeping breaks any download in progress.

I'm also noting that when two proxies share the same directory, one proxy's clear_partials sweep could delete the other proxy's in-flight temp files too — the code seems aware of this scenario given comments about pid and shared directories. The rest of the route/query handling around dry_run and sweep parameters looks fine and deliberate.

Now I want to double-check the config validation, whether cache_min_age is checked against sweep_interval, and verify parse_duration and the router setup in main.rs to make sure the spawn logic and route merging line up correctly.
Now let me check the config and main files, and the Cargo.toml for the toolchain (the `Duration::from_hours`/`from_mins` constructors are worth verifying).
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↳ read_file: read pr/services/proxy/src/config.rs
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↳ read_file: read pr/services/proxy/Cargo.toml
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↳ read_file: read pr/services/proxy/src/main.rs
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-- reasoning --
I'm spotting a real race condition: a blob that's just been committed to storage but whose index entry hasn't been written yet looks "unreferenced" to the sweep logic, and since the age check only applies elsewhere, it could get deleted immediately regardless of the min_age setting.  This defeats the intended purpose of that grace period — protecting freshly fetched blobs so later jobs in the same pipeline can reuse them — and would force an unnecessary refetch rather than causing outright corruption, since a stream already in progress on Unix survives the unlink.

Second, I realize `clear_partials` is far more dangerous: it wipes every file in `incoming/` unconditionally, including temp files for downloads actively in progress right now. The doc's claim that a file there means "a fetch that is not coming back" is false, and since commit relies on renaming that temp file, deleting it mid-download makes the rename fail and kills the in-flight fetch — a real high-severity bug triggered by any periodic or admin sweep. I also confirm the dry-run counting logic for partials is fine, just incrementing a counter per entry regardless of size.

Then I spot a metrics field-ordering swap: the counters list defines blobs-removed before bytes-reclaimed, but the values() function returns them in the opposite order, so bytes-reclaimed data gets labeled as blobs-removed and vice versa — exactly the class of bug the code comment warns against, and clearly a genuine defect.

Finally I notice the admin sweep endpoint calls the sweeper's sweep function directly instead of the wrapped run() method, bypassing the mutex meant to guarantee only one sweep runs at a time — so an admin-triggered sweep can execute concurrently with the background sweep despite the module's stated invariant.

Since sweep() is a synchronous function doing a full filesystem walk across potentially tens of thousands of directories, calling it from an async handler blocks a tokio worker thread for the entire duration; neither the admin route nor the background scheduler wraps it in spawn_blocking, even though their own comments acknowledge large sweeps can legitimately take over ten seconds, which would stall the runtime.

I'm also noting the `remaining >= self.max_bytes` comparison seems to trigger eviction even when storage sits exactly at the ceiling, though this is a minor edge case that's arguably still correct given how "within the ceiling" is defined.

I'm trying to recall whether `Duration::from_hours`/`from_mins` are stabilized yet — I believe they landed around Rust 1.89 under `duration_constructors_lite`, but without a toolchain check I can't confirm confidently, so I'll skip flagging this unless there's a rust-toolchain file to verify against. Now I'm looking at the symlink handling comment in the `collect` function, checking whether it correctly describes how `fs::metadata` follows links versus reporting link size.

Actually, I realize the comment is wrong: since `fs::metadata` follows symlinks rather than using `symlink_metadata`, a symlinked blob gets counted at its target's size, and a symlink pointing to a directory would cause recursion outside the intended store — contradicting the stated intent, so this is a real doc/behavior mismatch around line 164, worth flagging at low-to-medium severity. Next I'm checking whether `forget` is called unconditionally during sweep even when `dry_run` is enabled, since deleting index entries during a dry run would be a correctness issue.

Even in dry run, `gone` still gets populated with every removal candidate, and `forget` unconditionally calls `fs::remove_file` on their index entries despite blobs staying in place — so a dry run silently deletes real index entries while leaving the blobs orphaned, making them unreachable until refetch and then flagged as unreferenced garbage on the next sweep. This directly contradicts the documented "without removing anything" behavior for `dry_run=true`, so I'm confident this is a critical bug at sweep.rs:140, confirmed by the code showing `forget` has no dry_run parameter at all.

Beyond that, metrics get over-reported when `remove_file` fails for reasons other than NotFound (e.g. permissions), since `removed`/`bytes` are still counted and `gone.push` still triggers index deletion for a blob that was never actually removed — a minor issue. There's also a shared-directory race where temp paths include a pid but multiple proxies sharing the same directory means sweep can delete another proxy's in-flight partial upload, mirroring the earlier min_age guard bug since `clear_partials` never checks age at all. I also want to verify that the admin route correctly parses `dry_run=true` from the query string via serde's bool deserialization.

Looking closer, the sweep ordering has a subtle flaw: because candidates are sorted by age and unreferenced blobs are removed unconditionally while referenced ones are only trimmed down to the ceiling, a young unreferenced blob near the end of the list can cause old referenced blobs to be evicted first just to get under the threshold before the young unreferenced one is even counted — a marginal over-removal case not worth flagging. There's also the fact that age is based on mtime rather than access time, so a blob someone fetched this morning still looks stale if it was written long ago.

I also realize the eviction logic isn't actually LRU despite what the docs imply — mtime is only set at write time, so repeated reads never refresh it, meaning a frequently-fetched blob can still get evicted once its age exceeds min_age, contradicting the doc's claim that active use keeps a blob around for the next job in a pipeline.

Let me verify the commit-then-link ordering in cache.rs for that first race condition, and check routes/mod.rs for the router change plus whether sweep() is used elsewhere as a public sync call.
Let me check the cache serve path to confirm the commit/link ordering relative to the sweep's "unreferenced" rule.
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↳ read_file: read pr/services/proxy/src/routes/cache.rs
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-- reasoning --
I'm spotting a race condition: sweep can delete a freshly committed blob before it gets linked, since sweep only checks whether the blob is in the index, without accounting for the gap between commit and the later register_version/link calls in cache.rs.

Also, the ordering of reading the index snapshot before collecting candidate blobs makes this worse — a blob linked in between wouldn't be in the snapshot yet and could get wrongly deleted; collecting blobs first, then reading the index, would be safer, though not a complete fix.

I'm also noticing `clear_partials` removes every file in `incoming` with no age or liveness check, so a sweep running during an active fetch could unlink the temp file mid-write, causing the later rename-to-commit step to fail with NotFound and the fetch to error out — meaning concurrent fetches can fail whenever a sweep happens to run. That contradicts the assumption that files in `incoming` are always abandoned. This is another high-severity issue, separate from the BlobWriter's Drop-time warning logging on removal failure, which is minor by comparison.

Then I catch a metrics ordering bug: the COUNTERS array lists blobs_removed before bytes_reclaimed, but the values() function returns them in the opposite order, so the two metrics get swapped when rendered — bytes_reclaimed_total would actually show the blob count and vice versa, which is exactly the kind of mismatch the code comment warns about avoiding. That's a clear, medium-to-high severity bug since operators alerting on that metric name would get the wrong signal.

Now I'm turning to the admin sweep route to check whether it's blocking the async runtime by calling something synchronous.

Both the admin route handler and the background sweep task call the synchronous filesystem sweep directly inside async contexts without using spawn_blocking, meaning a sweep across tens of thousands of directories could stall a tokio worker thread for the full duration — and the module's own docs admit sweeps can take over ten seconds, which would starve other tasks scheduled on that thread. This is a genuine defect that should use spawn_blocking instead, appearing at both admin.rs:76 and main.rs:116, and I'd rate it medium-high severity. Now I'm checking whether the admin route also bypasses the mutex that should serialize sweep operations.

Without a known MSRV in Cargo.toml, I can't confidently flag the const-context Duration constructors as broken, so I'll skip that one. Then looking at the `remaining >= self.max_bytes` check — being exactly at the ceiling arguably still counts as "within" the limit, so using `>=` instead of `>` might be overly strict, cutting off one valid byte at the boundary.

Checking that `forget` properly removes index entries for blobs evicted due to exceeding the ceiling, so no stale entries remain there — that's correctly handled. For the over-ceiling eviction loop, since candidates are sorted oldest-first and it uses `continue` rather than `break` once a candidate's age is below `min_age`, I need to verify that doesn't cause it to skip over younger blobs incorrectly rather than stopping the loop entirely.

Actually, I realize the sort key is ascending by age, meaning youngest blobs come first, not oldest — despite the comment claiming "oldest first." That means the sweep would evict the most recently used blobs before the truly old ones, inverting the intended LRU behavior, which looks like a genuine high-severity bug rather than a nitpick.

Moving on, I'm scanning the rest of the sweep logic — dry-run accounting for unreferenced blobs and partials, how index candidates are collected with age/size, and the metrics recorded when the background sweep runs on its interval — checking each for similar correctness issues.

I'm double-checking the router and query parsing: the sweep route's timeout handling, whether admin auth ordering matters for a bad query string, and that `dry_run=true` deserializes correctly as a bool. Then I notice something concerning — in dry-run mode, `forget` is still invoked on the index and the "gone" list is populated unconditionally, meaning dry-run may not actually be side-effect-free.

Confirming this makes the "dry run reports without removing" documentation claim false. Checking other issues too: metrics swap confirmed, min_age zero is intentionally fine, two proxies sharing a blob dir means clear_partials can delete another process's in-flight temp files similar to the earlier bug, and I'm noting that removing unreferenced blobs still counts toward getting under the size ceiling.

Now I'm assigning severity to the findings: dry_run destroying cache reachability by deleting index entries is critical, the ascending sort evicting newest blobs instead of oldest is critical, and the race where a committed-but-not-yet-linked blob gets deleted without min_age grace causing in-flight cache misses is high severity.

More findings emerge — clear_partials removing live in-progress temp files without age checks breaking concurrent commits, metrics.rs swapping value order so counters are mislabeled, admin.rs bypassing the running mutex so two sweeps run concurrently and over-evict, and finally admin.rs/main.rs doing a synchronous multi-second filesystem walk on the async runtime thread instead of spawning it as blocking work.

I check if these const constructors are actually stabilized for the MSRV — but the existing tests already use from_mins, so the toolchain clearly supports it already, making this a non-issue. That settles the final list at 7 findings.
Everything needed is in hand. Findings:

🔴 `bug` services/proxy/src/sweep.rs:140: `forget(&index, &gone)` is not gated on `dry_run` and `gone` is filled even in a dry run (lines 136-137 run unconditionally), so `POST /v1/admin/cache/sweep?dry_run=true` really unlinks the index entries of every blob it merely reported — the blobs it "did not remove" become unreachable cache misses immediately and are deleted as unreferenced on the very next real sweep, the opposite of the documented "reports … without removing anything".

🔴 `bug` services/proxy/src/sweep.rs:102: `sort_by_key(|c| c.age)` orders candidates **youngest first** (smallest `now - mtime` first), yet the eviction loop removes from the front, so an over-ceiling sweep deletes the most recently fetched blobs and keeps the oldest — an inverted LRU that thrashes exactly the packages current builds are using; the sort needs to be descending by age.

🟠 `bug` services/proxy/src/sweep.rs:119: a blob with no index entry is removed with no `min_age` grace, but on the miss path a blob exists unlinked for the whole window between `writer.commit()` (services/proxy/src/routes/cache.rs:151) and `store.link()` (cache.rs:163), which includes a network round-trip to the registry — a sweep in that window deletes the just-committed blob and the request 500s at cache.rs:90; reading the index snapshot (line 92) *before* walking blobs (line 95) widens the race further.

🟠 `bug` services/proxy/src/sweep.rs:230: `clear_partials` unlinks every file in `incoming` with no age or liveness check, but `incoming` is where `BlobWriter` (store.rs:171-180) is actively writing in-flight downloads — a sweep during a fetch unlinks the live temp file, and `commit`'s `fs::rename` (store.rs:259) then fails with NotFound, failing the request; the doc's claim that "a file in `incoming` is a fetch that is not coming back" is false while any fetch is in flight.

🟠 `bug` services/proxy/src/metrics.rs:94: `values()` loads `sweep_bytes_reclaimed` at index 4 and `sweep_blobs_removed` at index 5, but `COUNTERS` (lines 50-57) names index 4 `cairn_proxy_sweep_blobs_removed_total` and index 5 `..._bytes_reclaimed_total` — each sweep counter is exported under the other's name, which is precisely the mix-up the comment on `COUNTERS` warns about, and docs/operations.md tells operators to alert on the bytes counter that will actually carry the blob count.

🟠 `bug` services/proxy/src/routes/admin.rs:76: the admin route calls `app.sweeper.sweep(dry_run)` directly instead of `run()`, skipping the `running` mutex (sweep.rs:83), so an on-demand sweep runs concurrently with the background sweep (or another admin sweep) — the exact two-sweeps-over-one-total situation the module doc (sweep.rs:10-12) says must never happen, each deleting from a total the other is changing.

🟡 `performance` services/proxy/src/routes/admin.rs:76: `sweeper.sweep()` is a fully synchronous filesystem walk (readdir + stat over up to 65k directories, plus reading every index file) executed inline on a tokio worker thread — routes/mod.rs:125 itself says a sweep "legitimately takes longer than ten seconds" — blocking that runtime thread for the duration; the same applies to `app.sweeper.run().await` in the spawned task at services/proxy/src/main.rs:116; both should go through `spawn_blocking`.
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