sandbox:read-only (macOS Seatbelt)
-- reasoning --
I want to check the relevant files under `pr/` for context—sweep.rs, store.rs for layout and blob writing, admin routes, and config.rs, particularly whether `Duration::from_hours` is stable in the Rust version being targeted.

Now I'm hunting for concrete defects: the admin route's reclaim handler appears to call the sweeper's sweep function directly without acquiring the running lock, meaning an admin-triggered sweep could run concurrently with the scheduled interval sweep despite the module's promise of mutual exclusion. I'm also noting that sweep performs blocking filesystem calls but runs inside async context, which could stall the tokio executor during large sweeps that legitimately take longer than ten seconds.

I'm now examining the eviction threshold logic and the sorting of removal candidates, checking edge cases around the max_bytes comparison and minimum age skipping, and I've spotted a potentially serious race condition: the partial-file cleanup sweeps the incoming directory and deletes every file there, which could include files actively being written by an in-progress fetch.

I need to trace how BlobWriter finalizes files -- if unlink happens while the writer still has the file open, the eventual rename to finalize the fetch would fail with ENOENT, breaking any concurrent download. There's also a similar race between the sweep and normal blob writes: if a blob is renamed into the blobs directory before its index entry is committed, the sweep could see it as unreferenced and delete it prematurely.

I also notice a potential bug in dry-run mode -- `sweep` calls `forget` unconditionally regardless of the dry_run flag, so I need to check whether `forget` actually removes files, which would mean dry-run isn't truly non-destructive.

Continuing to trace this, I find the values array pushes bytes_reclaimed at index 4 and blobs_removed at index 5, while the COUNTERS array has blobs_removed at index 4 and bytes_reclaimed at index 5 — confirming the swap bug where the fifth counter renders under the fourth one's name.

Then I consider the eviction threshold check comparing remaining bytes to max_bytes using `>=` rather than `>` — this seems like a minor edge case rather than a real bug, since removing exactly at the ceiling is a defensible interpretation of "the most the store may hold."

Checking the metrics recording for sweeps, it's consistent between main.rs and the admin route. The query deserialization for dry_run as a boolean works fine with serde_urlencoded. But I notice spawn_sweeps calls the sweeper's run method while holding a lock, and even though run is async, it ends up blocking the runtime synchronously during the sweep. Then looking at the collect function, I realize fs::metadata follows symlinks by default, which contradicts the code's own comment claiming that a link is counted at the link's size rather than the target's size — that's a real discrepancy worth flagging.

Following on from that, this same behavior could cause infinite recursion if there are symlinked directory cycles, since fs::metadata traverses through them during collection. Now I'm digging into clear_partials, which deletes in-flight partial writes without checking whether the writer is still active or applying a minimum age — meaning an active download's temp file could get deleted mid-write.

That would break in-flight fetches since a rename attempt from a now-deleted path would fail with ENOENT, making this a high severity issue. Then there's a related race: if the sweep runs between a blob write/rename and its index entry being written, the blob could get deleted before the index even points to it, potentially leading to broken references or false hits depending on how BlobStore::resolve validates blob existence.

I'm also flagging that admin.rs's reclaim handler runs sweep synchronously and blocks the worker thread while bypassing the mutex fix from finding 1, and separately need to check whether Duration::from_hours/from_mins usage is compatible given the crate's rust-version in Cargo.toml. I should go read the actual PR files now to verify these against the real code.
I'll read the changed files plus the store module the sweep depends on.
└ 3482 tok ·  75.1 tok/s · 19K ctx · 4531ms ttft · 46.4s wall
↳ 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/routes/admin.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-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 found that the values() order in metrics.rs is swapped relative to COUNTERS—blobs_removed and bytes_reclaimed are listed in one order but returned in the other, causing each metric to be rendered under the wrong name. This matches exactly the bug the code comment warns about, so it's a high severity issue.

Next, clear_partials in sweep.rs unconditionally deletes every file in the `incoming` directory, but that directory also holds in-progress writes from active fetches—the doc comment claiming a file there means "a fetch that is not coming back" is simply incorrect. On Linux this unlinks the file while the writer still has an open fd, so the write succeeds but the final rename fails with NotFound, meaning any concurrent fetch breaks whenever a sweep runs; min_age also isn't respected here. That's another high/critical bug.

Then I check the sweep eviction condition based on remaining bytes versus max_bytes, which looks like the correct semantics for bringing the store back under the ceiling.

But there's a real concurrency bug: the admin `reclaim` route calls `sweeper.sweep()` directly without acquiring the `running` mutex the background sweep task uses, so a manual sweep can run concurrently with a scheduled one, violating the "one sweep at a time" invariant the module docs explicitly warn about—this causes over-eviction.

Also noting that `Sweeper::run` calls the synchronous `sweep()` function directly inside a tokio async task, meaning the filesystem walk blocks the async runtime.

Even worse, I'm spotting that `forget` is called unconditionally after building the removal set—even during dry runs—which means dry-run mode still deletes real index entries for blobs it only pretended to remove, making those blobs unreachable afterward.

And if a subsequent real sweep runs, it'll treat those now-indexless blobs as unreferenced and delete them regardless of age, so dry_run isn't actually side-effect free — this looks like a critical bug around sweep.rs line 140. There's also a minor issue where forget strips index entries even when the underlying file removal fails, and I want to double check the `remaining` count logic against `held` when unreferenced blobs are removed.

There's a deeper race though: a blob could get renamed into place before its index link is written, so if the sweep runs in that window it'll see an unreferenced blob and delete it outright since age doesn't matter for unreferenced entries — then the link gets written pointing at a now-deleted blob. I need to check cache.rs to see whether the serving path streams the file it just wrote or reopens it from disk, since that determines whether this race actually breaks a live request.

I'm also noting that the sweeper runs blocking synchronous IO inside async spawned tasks, and flagging that config.rs uses `Duration::from_hours`/`from_mins`, which I believe are still gated behind the unstable `duration_constructors` feature rather than being stable APIs.

Let me look at cache.rs to confirm the in-flight race condition, and check routes/mod.rs for additional context.
Now let me check the cache route to see how fetches interact with `incoming/` and the index-link ordering.
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↳ read_file: read pr/services/proxy/src/routes/cache.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/main.rs
└ read_file: read complete
-- reasoning --
I'm spotting a defect: the sweep unconditionally deletes everything in the incoming directory, including partial files still being actively written by an in-progress fetch, since it clears the whole directory rather than checking file age or write state.

Second, sweep.sweep runs synchronous std::fs operations directly on the async runtime without spawn_blocking, which could stall the tokio worker thread for the entire duration of a large sweep -- something the docs themselves admit can take longer than ten seconds.

Third, I'm spotting a race window in cache.rs's fetch flow: a blob gets renamed into the blobs directory before its index entry is written (there's a registry network round-trip in between), so a sweep running during that gap would see the blob unreferenced and delete it regardless of its age.

Actually, digging deeper: `forget` is called unconditionally at line 140 regardless of dry_run, and `forget` itself has no dry_run gating — so `?dry_run=true` actually deletes index entries via real `fs::remove_file`, contradicting its "without removing anything" promise. This is critical: dry run mode destroys cache references, causing every subsequent request to miss and refetch.

I'm also spotting a metrics ordering swap — the values tuple returns bytes_reclaimed then blobs_removed, but COUNTERS lists blobs_removed_total first then bytes_reclaimed_total, so the labels get mismatched and the numbers are swapped in the output.

There's also a concurrency issue: the admin reclaim handler calls sweeper.sweep(dry_run) directly instead of going through run(), bypassing the running mutex entirely — so an admin-triggered sweep can run concurrently with a background sweep or another admin request, violating the "one sweep at a time" invariant.

Then I'm checking the eviction stop condition against the max_bytes ceiling — it removes while remaining >= max_bytes, so at the exact boundary (remaining == max_bytes) it triggers one extra unnecessary removal even though that state is already within the ceiling. Minor and borderline, but worth flagging.

I'm also noting the byte counter increments even when a removal fails or the blob is already gone, which slightly overcounts removed bytes — a minor cosmetic issue, especially visible in dry-run mode where nothing is actually deleted.

Then I'm checking whether `Duration::from_hours` and `from_mins` are stable Rust APIs or still gated behind the nightly `duration_constructors` feature, trying to recall the exact stabilization timeline.

Separately, I'm looking at a symlink handling bug: the code uses `fs::metadata`, which follows symlinks and returns the target's size, but the comment claims it counts the link's own size — that would require `symlink_metadata` instead, so the comment contradicts the actual behavior.  This means sweep sizing and deletion logic can traverse through symlinks and act on the target rather than the link itself, which could remove or size the wrong data.

Continuing to scan for smaller issues: double-counted background task metrics between main.rs and the admin route seem fine since they're separate sweeps. The forget path deleting index entries even when blob removal fails for reasons other than NotFound (like permissions) could orphan a live blob, though that's a minor issue. I'm also noting blob age is measured from initial write time via mtime.

Since mtime never updates on cache hits, eviction is really oldest-written rather than true LRU — a blob fetched constantly for months but written long ago would get evicted before a cold blob cached yesterday, which contradicts the docs' claim that min_age protects "a package one job in a pipeline fetched." The sweep.rs comment describing eviction as targeting "the blobs nothing has wanted for longest" is misleading since age tracks write time, not last-access time. This design/behavior mismatch seems worth flagging as a moderate concern.

I'm also noting that dry-run ordering removes partials for real even when in-flight, connecting back to bug #1, and checking whether the sweep route's query deserialization for `dry_run=true` actually parses correctly as a bool. I want to confirm min_age validation allows zero as a valid grace period, and check Cargo.toml for the rust-version to verify `from_hours` stability.

I'm also confirming bug #4: the `forget` call is unconditional even in dry_run mode, meaning it deletes real index entries for blobs that were only hypothetically marked for removal — this looks critical. I don't see any double-counting issue between background sweep and admin metrics, and I'm now tracing how main.rs's run() function invokes sweep.

Additionally, admin's sweep bypasses the mutex lock that the regular sweep holds, so I'll flag that separately. The `reclaim` function is another synchronous call invoked from an async handler, blocking the handler thread just like issue #2 — since both defects live at admin.rs:76, I'll report them as two distinct findings rather than merging them. Similarly, the interval loop in main.rs calls sweep synchronously inside an async context without spawning a blocking task, which stalls a runtime worker thread — I'll cite sweep.rs:84 for that. Now I need to check Cargo.toml for the rust-version field to verify which language edition features are actually available.
Let me check the Cargo.toml for the Rust version (the config uses `Duration::from_hours`/`from_mins`, which were only recently stabilized) and the config file itself.
└ 4353 tok ·  70.4 tok/s · 39K ctx · 5859ms ttft · 61.8s wall
↳ read_file: read pr/services/proxy/Cargo.toml
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/config.rs
└ read_file: read complete
-- reasoning --
I'm examining a bug where clear_partials wipes files in incoming/ indiscriminately, even ones that are actively being written by an in-progress fetch — which would break the later rename during commit since the source path would no longer exist.

There's also a race where a blob committed to disk but not yet linked in the index could get swept as "unreferenced" since the unreferenced-deletion path ignores min_age entirely, unlike the age-gated stale-partial path.

I'm also noticing a minor off-by-one: the eviction condition uses `>=` against max_bytes, so it evicts even when the store sits exactly at capacity rather than only when it exceeds it, which is a subtle deviation from the documented "most the store may hold" semantics.

Then I catch a clearer bug in metrics.rs: the COUNTERS list declares blobs_removed_total before bytes_reclaimed_total, but the values() function loads bytes_reclaimed first and blobs_removed second, so the two metrics get mismatched and reported under each other's names — a real, medium-to-high severity issue at lines 94-95.

I also want to check whether `Duration::from_hours`/`from_mins` are actually stable in the Rust version being used, since I recall these constructors being gated behind the `duration_constructors` feature and possibly still unstable.

Now I'm spotting a real concurrency bug: the admin sweep route calls `sweeper.sweep(dry_run)` synchronously from the async handler without `spawn_blocking`, blocking a runtime worker on a filesystem walk that could take minutes. Worse, it bypasses the `running` mutex that `Sweeper::run` normally acquires, so an admin-triggered sweep can execute concurrently with the background sweep — violating the module's documented "one sweep at a time" guarantee.

I'm also finding a dry-run correctness bug: `forget` is called unconditionally regardless of dry_run status, and it actually deletes index entries via `fs::remove_file` with no dry_run check. So a supposed "dry run" still deletes index entries for blobs it identified for removal, while leaving the actual blob files in place — orphaning them until the next real sweep cleans them up.

Checking a few smaller issues: if `remove_file` on a blob fails, its index entries are still dropped from `gone`, which just causes an extra refetch later — minor, error-path only. Eviction ordering by age looks correct, and decrementing `remaining` during dry_run is fine since it's just simulating the outcome.

Then I trace another possible race: clear_partials could theoretically delete an index temp file mid-rename, causing a link failure right after a successful download — the same class of bug as the earlier race. I check the sweep interval timer, the route's placement outside the timeout layer, and the query deserialization, all of which look fine, before moving on to how spawn_sweeps interacts with graceful shutdown.

The task keeps running until process exit as documented, and I confirm the metrics recording paths — the admin sweep route bypasses the mutex and risks double-recording, which I've already flagged. I also verify that blobs with future mtimes get treated as age zero and sorted as newest, which is fine, and I re-examine the eviction loop's threshold check to confirm young blobs are correctly skipped while still counting toward remaining bytes, and that exhausting all eligible old blobs without reaching the ceiling is expected behavior.

Regarding `Duration::from_hours`, I recall the `duration_constructors_lite` feature stabilizing around Rust 1.91, so given this repo's dependencies look futuristic (fictional-seeming versions like reqwest 0.13.4 and sha2 0.11), I won't flag this API as unstable since it's plausible the intended toolchain supports it.

Looking deeper at the sweep logic, the real concern is that a blob renamed into place but not yet linked in the registry has zero age grace under the unreferenced-blob path — a concurrent sweep could delete it during the window while `register_version`'s network call is still in flight, which is a genuine race condition around sweep.rs:119-120.

There's also #1: `clear_partials` can delete an in-progress temp file mid-download, spanning the full transfer duration for a large artifact — this would break `BlobWriter::commit`'s rename with a NotFound, surface as a 500 to the client, and trigger a redundant warning on Drop. That's high severity given the loop at sweep.rs:224-238.

Separately, the mutex bypass at admin.rs:76 should be routing through `run()`, and `reclaim` being a synchronous full-directory walk called from an async handler risks blocking a worker thread on large stores — worth flagging as its own medium-severity issue alongside the mutex bypass.

I'm also noting the background sweep task runs its synchronous walk directly on a runtime worker instead of via `spawn_blocking`, which stalls other tasks for the whole sweep duration — medium severity at sweep.rs:84 and admin.rs:76. And there's a metrics ordering bug at metrics.rs:94-95 where the bytes value gets attributed to the blobs_removed counter, which would mislead any operator relying on that metric.

Then there's a more serious dry-run bug at sweep.rs:140: `forget` is invoked even when dry_run is set, so it deletes real index entries for everything the sweep would have removed. That not only breaks the current dry run but leaves those blobs unreferenced, guaranteeing the next real sweep deletes them regardless of the ceiling — this deserves a red flag. I'm also weighing whether the clear_partials race is red or orange, since any sweep overlapping with an in-flight download will fail that download, and sweeps run every 15 minutes.

I'm settling on orange-high for the partials race — it's recoverable via client retry but happens routinely. The unreferenced-blob race gets a similar orange. For the dry-run deleting index entries, I lean orange too, since it only causes cache misses/refetches rather than permanent data loss, even though it violates the "without removing anything" contract. The metrics swap issue feels more like yellow-to-orange since it corrupts alerting data but isn't destructive, so I'll call it yellow. The mutex bypass allowing concurrent sweeps to double-count and over-evict also seems like a medium/orange issue, since it contradicts the module's concurrency guarantees when both a background and admin sweep run at once.

Blocking the runtime worker feels like a yellow-severity issue, and I'm also checking the off-by-one in the byte threshold comparison, which seems like a low-severity blue issue. I'm double-checking whether dry-run counts include partial entries correctly, confirming the reclaimed partials tracking looks fine, and verifying that directory recursion handles metadata properly without unnecessary overhead. I'm also glancing at the env example header ordering and the sweep recording call signature to make sure everything lines up.

Now I'm compiling the actual findings: the real critical issue is that `forget` runs unconditionally even in dry-run mode, meaning dry-run isn't actually dry — it deletes live index entries so a subsequent real sweep would remove things regardless of ceiling or age checks. There's also a second critical issue in `clear_partials`, which deletes every file in the incoming directory without any age check, wiping out temp files from in-flight downloads or link operations, which then causes the later rename calls in store.rs to fail.

Beyond that, I'm noting a race where unreferenced-blob removal ignores min_age, so a blob that's been committed but not yet linked (since the index write happens after a registry round-trip) can be deleted by a concurrent sweep, producing a 500. I also see the counters in metrics.rs get swapped because values are loaded in a different order than they're listed, and admin.rs calls sweeper.sweep() directly, bypassing some expected safeguard.

Now I'm double-checking severity and line references: the admin sweep bypasses the running mutex that run() takes, so it can execute concurrently with the background sweep and break the one-at-a-time invariant, causing double counting or over-eviction. There's also a synchronous filesystem walk running on the async runtime without spawn_blocking, which stalls the worker, and an off-by-one in the eviction threshold check that evicts even when the store is exactly at its configured ceiling. I'm pinning down exact line numbers for each of these issues now.
🔴 `bug` services/proxy/src/sweep.rs:140: `forget` is called unconditionally, so a `dry_run=true` sweep deletes the real index entries (`fs::remove_file` at line 252) for every blob it merely *would* have removed. A "dry" run therefore mutates the store: those coordinates become misses, and the now-unreferenced blobs are deleted by the next real sweep regardless of ceiling or age — the exact opposite of the route's "reports without removing anything" contract.

🔴 `bug` services/proxy/src/sweep.rs:232: `clear_partials` unlinks every file in `incoming/` with no age or ownership check, but that directory holds the temp files of downloads *currently in flight* (`BlobStore::temp_path`, store.rs:201) and of index writes (`link`, store.rs:148). A sweep landing during a fetch unlinks the temp file, so the later `fs::rename` in `BlobWriter::commit` (store.rs:259) or `link` (store.rs:152) fails with NotFound and the client request 500s; every download active at each 15-minute sweep is at risk.

🟠 `bug` services/proxy/src/sweep.rs:119: unreferenced blobs are removed with no `min_age` grace, but on the miss path a blob is committed to `blobs/` (cache.rs:151) before its index entry is written (cache.rs:163) — with a registry network round-trip in between. A sweep in that window sees a fresh, referenced-in-a-moment blob as orphaned, deletes it, and the request fails with the "blob committed by this request is already missing" 500 at cache.rs:90-97.

🟠 `bug` services/proxy/src/metrics.rs:94: `values()` loads `sweep_bytes_reclaimed` before `sweep_blobs_removed`, but `COUNTERS` (lines 50-57) lists `cairn_proxy_sweep_blobs_removed_total` first, so each value is exported under the other counter's name — the exact swap the comment above `COUNTERS` warns about; dashboards/alerts on `sweep_bytes_reclaimed_total` will show blob counts.

🟠 `bug` services/proxy/src/routes/admin.rs:76: the admin route calls `app.sweeper.sweep(dry_run)` directly, bypassing the `running` mutex that only `Sweeper::run` (sweep.rs:83) takes. An on-demand sweep can run concurrently with the background sweep, breaking the module's one-sweep-at-a-time invariant (sweep.rs:10-12): both compute removal sets from the same snapshot, over-evict below the ceiling, and double-count the reclaimed bytes in metrics.

🟡 `performance` services/proxy/src/routes/admin.rs:76: `Sweeper::sweep` is a synchronous walk of the whole store (up to 65k directories plus the full index) called directly from an async handler (and from the async task via `run()` at sweep.rs:84) with no `spawn_blocking`, so a sweep of a large store pins a tokio worker thread for its entire duration and stalls every other task scheduled on it.

🔵 `bug` services/proxy/src/sweep.rs:120: the eviction condition `remaining >= self.max_bytes` removes a blob when the store is exactly at the ceiling, contradicting the config's definition of `cache_max_bytes` as "the most the blob store may hold" (config.rs:63); should be `>`.
└ 6346 tok ·  74.2 tok/s · 43K ctx · 4549ms ttft · 85.6s wall