sandbox:read-only (macOS Seatbelt)
-- reasoning --
I should check the actual files to verify, since I suspect `Duration::from_hours`/`from_mins` might still be unstable nightly-only APIs in Rust's standard library rather than stabilized ones, which could be causing a compile issue.

The sweep logic looks fine—removing candidates until remaining drops below max_bytes, sorted oldest first respecting min_age. But I'm spotting a real bug: in dry_run mode, `forget` is still called unconditionally on the `gone` list, which deletes index entries via fs::remove_file regardless of dry_run status. That means dry run would actually remove index entries pointing to blobs that are still physically present, orphaning them.

I'm also noticing a concurrency issue: the admin route's `reclaim` handler calls `sweeper.sweep(dry_run)` directly, bypassing the `running` mutex that `run()` uses to enforce single-sweep-at-a-time. That lets an admin-triggered sweep run concurrently with a background sweep, violating the intended invariant. Additionally, `run()` executes the synchronous filesystem walk directly inside an async function while holding the tokio mutex, blocking the executor thread during what could be a large directory traversal.

There's also a race between sweep and in-progress writes: since blobs are renamed into place before their index entry is written, a fetch that just completed the rename but hasn't yet written the index entry looks identical to an orphaned blob to the sweeper, so a brand-new blob could get deleted even though "age does not enter into" that first removal condition.

Worse, clear_partials wipes everything in the incoming directory without checking age, but incoming is exactly where active fetches keep their temp files while writing — deleting one mid-write means the writer's fd is now pointing at an unlinked path, so the eventual rename fails and the fetch errors out. I need to check store.rs to confirm incoming really holds in-flight writes and see if there's any locking or age check I'm missing.

Then in the metrics code, the comment about keeping two counters side by side to prevent a fifth counter rendering under a fourth's name is ironic, because the actual order is swapped: COUNTERS lists blobs_removed then bytes_reclaimed, but values() loads bytes_reclaimed first and blobs_removed second — so the labels and values are definitely mismatched.

I also want to flag that using `Duration::from_hours`/`from_mins` relies on an unstable API that won't compile on stable Rust, so I should check the Cargo.toml or rust-toolchain file to see what toolchain this project targets.

Looking at dry-run behavior, clearing partials and counting bytes without deletion seems correct for reporting purposes, and the sweep logic that keeps removing while remaining size is at or above the max threshold looks right too. Now I'm trying to figure out how unreferenced blobs get matched against the index — checking whether the file name used is the full hex digest or just a fragment, since blob storage likely uses fan-out subdirectories under blobs/sha256, so I need to look at store.rs to understand the actual layout before judging if the containment check is correct.

If blobs are stored with the hex split into a prefix directory and a remainder file name, then comparing that remainder against full-hex index keys would never match, meaning every single blob would look unreferenced and get deleted — that's a serious bug worth flagging once I confirm the layout in store.rs. I also want to check that forgetting index entries after a real sweep works correctly while dry-run mode properly avoids mutating anything, and note the admin route running sweep outside the timeout window seems fine either way.

Then there's the background sweep interval: tokio's `interval` actually fires its first tick immediately rather than waiting one interval, so the comment claiming otherwise is incorrect — this means a sweep fires right at startup instead of after a delay as intended, which is a low-to-medium severity bug in the initialization logic.

Now I want to trace through the actual source to confirm all this: checking the store's file layout and IndexEntry structure, write ordering, digest handling, the routes module, config duration parsing, and toolchain edition logic for the hours conversion — I need to read these files directly to verify.
I'll read the key files to verify the sweep logic against the store layout and the surrounding code.
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↳ 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/config.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'm spotting a mismatch in metrics.rs: the COUNTERS list order doesn't match the order returned by values(), so sweep_bytes_reclaimed and sweep_blobs_removed end up swapped under each other's names.

Also finding that admin::sweep calls sweeper.sweep() directly, bypassing the running mutex that enforces one sweep at a time — this can race with the periodic run(). Plus, sweep() does a synchronous blocking filesystem walk (potentially tens of thousands of directories) called directly from async handlers/tasks without spawn_blocking, which would block a tokio worker thread.

I'm also realizing clear_partials removes every file in incoming/, including temp files for fetches currently in progress — the doc's claim that "a file in incoming is a fetch that's not coming back" is wrong, since active writers keep their temp file there until commit renames it. A sweep running concurrently with an active fetch would delete its temp file, causing the rename at commit to fail and killing that fetch, with no age check to protect recent partials.

There's also a race between sweep and concurrent link/fetch operations: since clear_partials, referenced(), and collect() run in sequence, a blob committed after the referenced() snapshot but before collect() could be seen as unreferenced and deleted, even though a link entry pointing to it gets written afterward — forcing a refetch on next serve, and worse, the min_age protection doesn't seem to apply to newly-unreferenced blobs in this window.  Checking the serve path in cache.rs now to see if it reopens the blob post-commit — if so, sweep could delete a just-committed blob before link() runs, causing a 404 mid-serve (sweep.rs:119, medium-high severity). Also flagging that forget() appears to delete index entries even when dry_run is set, which seems wrong.

Actually there's an even worse bug: dry_run still collects digests into `gone` and calls forget unconditionally at line 140, meaning a "dry run" request actively deletes index entries for blobs that are never removed — destroying future cache hits despite the dry run promising no changes. That's a critical bug at sweep.rs:140.

I'm also checking the boundary condition on the eviction loop — comparing remaining bytes strictly greater than max_bytes versus greater-or-equal could leave the store exactly at the ceiling, which technically satisfies "within max" per the docs, so this is a minor, low-priority nit. Then I'm glancing at whether `Duration::from_hours`/`from_mins` are stable APIs in the Rust version being targeted.

Those tests likely predate this change, so compilation should be fine there — moving on. Checking `record_sweep` call sites in main.rs and admin.rs, both pass removed/bytes correctly matching the signature.

Now I'm looking at the sweep execution paths: main.rs's loop calls the async sweeper.run() which does blocking work on the runtime thread, while admin.rs's reclaim route calls sweep directly and synchronously, bypassing the mutex entirely — meaning a concurrent admin-triggered sweep could run alongside the background sweep, causing the same double-sweep race I flagged earlier.

Reviewing the reference collection recursion in the index — looks fine. The held-file computation walks all files under the blobs directory, sorts by age, and removes oldest-first until under the byte limit, with unreferenced blobs also contributing to the reduction — that logic checks out. The zero-value case for cache_min_age seems intentionally permissive, allowing immediate eviction.

I want to double check the exact line numbers in routes/admin.rs and revisit cache.rs to confirm the incoming temp file race condition and the ordering between commit and serving.

I'm now confirming a metrics ordering bug — the bytes-removed value appears to be rendered under the blobs-removed counter name and vice versa, which is a real defect. I also verify that dry_run=true as a query parameter deserializes correctly as a boolean via serde, so that's fine. Let me actually read through admin.rs and cache.rs to pin down line numbers and trace the fetch flow.
Now let me check the admin route and the cache serve path to verify the fetch flow against the sweep.
└ 3082 tok ·  72.9 tok/s · 39K ctx · 4224ms ttft · 42.3s wall
↳ read_file: read pr/services/proxy/src/routes/admin.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/main.rs
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-- reasoning --
I'm spotting a race condition: the sweep in clear_partials deletes every file in incoming/ without checking age, so it could unlink a partial file that's still being actively written by an in-flight fetch, since there's no protection distinguishing stale partials from live ones.

I'm also flagging a second issue: Sweeper::sweep is a synchronous filesystem walk that gets called directly from async contexts (run() and the admin reclaim handler) without spawn_blocking, meaning it can block a tokio worker thread for potentially minutes on a large store, stalling the whole proxy.

Then there's a mutex bypass problem: admin::reclaim calls sweeper.sweep(dry_run) directly instead of going through sweeper.run(), so the "one sweep at a time" lock never gets held for admin-triggered sweeps. That lets concurrent admin requests, or an admin sweep racing a background sweep, run in parallel — exactly the scenario the module's own docs warn against.

Finally I'm checking the eviction loop's stopping condition, tracing through whether removing blobs while remaining size is >= max_bytes actually leaves the store correctly under the ceiling once the loop exits.

But there's a subtler bug: `remaining` gets decremented even when a blob removal fails or during dry runs, so the sweep can wrongly believe it's back under the ceiling when the failed deletions never actually freed space — and the removed/bytes metrics get incremented too, overstating what was cleaned up. Worse, I'm noticing `forget` is called unconditionally regardless of dry_run, meaning a dry run actually deletes index entries for blobs it merely intended to remove, even though the underlying blob files are untouched — leaving the index out of sync with reality.

Actually, checking the sort order more carefully: age is measured as time since modification, so an older blob has a larger age value. Sorting ascending by age puts the youngest blobs first, which means the removal loop deletes recently-modified blobs before old ones—directly contradicting the "oldest first" intent in the comment. That's another genuine bug at sweep.rs:102.

I'm also noting a separate issue in metrics.rs around lines 94-95, where sweep_bytes_reclaimed is loaded before sweep_blobs in the values() function, creating an ordering mismatch.

I'm trying to recall whether `from_hours`/`from_mins` are stabilized yet — I think it's around Rust 1.91, so this might depend on the toolchain in use. I should check Cargo.toml for a rust-version constraint before flagging it as an issue.

Checking the dry-run admin route, the eviction boundary logic, and whether sweep correctly scopes to the blobs directory rather than the index — these all look like minor semantic edge cases rather than actual bugs, though I want to look closer at potential race conditions during sweep.

Actually, I've found a genuine race: a blob just committed via rename but not yet linked in the index has no reference, so a sweep pass can treat it as unreferenced regardless of age and delete it — then the concurrent request that just wrote it fails with a 500 when it tries to open the blob. Since there's a registry round-trip between commit and link that can take seconds, a sweep landing in that window can kill an in-flight request, and the code comment there seems to wave away this exact scenario.

I also note a minor issue where failed blob removals still get their index entries deleted, leaking the blob until a later sweep catches it — low severity since it self-heals eventually.

More concerning: `tokio::time::interval` actually fires its first tick immediately rather than after one period, contradicting the doc comment claiming the first sweep is delayed to avoid scanning an unfilled cache. That's a real defect against the stated design intent, medium severity since it causes an immediate sweep at startup.

Continuing through the rest, the admin sweep route still runs its multi-second sweep synchronously in the async handler without spawn_blocking (same issue as before), the dry_run query parsing looks fine, and the metrics naming checks out apart from the earlier swapped-values bug. The dry_run reporting removed counts even though nothing is actually removed seems intentional given the route's semantics.

More critically, I'm catching that `collect` uses `fs::metadata` instead of `symlink_metadata`, which means it follows symlinks rather than measuring the link itself — directly contradicting the comment that claims links are counted "at the size of the link and not of whatever it points at." This is backwards, and worse, if a symlink points to a directory, the recursion could follow it and potentially delete files outside the store through the symlinked path.

I'm also noting smaller items: `remaining` decrementing during dry_run seems intentional, and `age` for referenced collect reuses collect but just wastes some work, nothing serious. Then I move to checking whether `Duration::from_hours`/`from_mins` in config.rs are safe against the crate's minimum rust-version, glancing at whether pre-existing tests already used those methods before this diff.

Then I go through several more spot checks: sweep intervals are validated nonzero before use so tokio won't panic, sweep ceiling comparisons only counting blob bytes are consistent with prior documentation, and the sweep route sitting outside the timeout block seems fine structurally. I also confirm that `record_sweep` calls from both the background spawn and the admin reclaim path don't double-count since they're separate sweep instances, before turning to consider how the mutex bypass interacts with concurrent admin sweeps.

Now I'm working through severity: dry_run still calls `forget`, which deletes index entries even during a supposed no-op run — that's a real bug since it makes cached blobs unreachable and turns them into garbage the next sweep cleans up, so dry run is actually destructive. And `clear_partials` unlinking everything in `incoming/` without any age check is dangerous because it could delete temp files for fetches still in progress.

I'm also flagging that `sort_by_key(age)` ascending evicts the youngest blobs first instead of the oldest, which contradicts the intended "oldest first" behavior; a swapped metrics label bug where blobs_removed and bytes_reclaimed are rendered under each other's names; and the admin bypass of `Sweeper::run` letting concurrent sweeps run in parallel and break the one-at-a-time invariant.

Beyond that, I'm noting a race where unreferenced blobs get removed without a grace period, so a blob committed but not yet linked can vanish mid-request and cause a 500; a synchronous filesystem walk running directly on tokio worker threads without spawn_blocking, which can stall the runtime for minutes; and a startup timing issue where `tokio::time::interval` fires immediately, contradicting the documented "first tick is one interval away" behavior and causing an unintended sweep at boot.

I'm also flagging that `fs::metadata` follows symlinks despite comments claiming otherwise, meaning symlinked directories get recursed into and their targets can be unlinked — plus removal failures still get counted toward removed bytes and forgotten index entries, overstating reclaim while leaving an orphaned blob behind. Double-checking the age-ascending sort against the removal loop confirms it evicts youngest-referenced blobs first, which is backwards for ceiling eviction — a confirmed bug.

Verifying the metrics indices: COUNTERS[4]/[5] map to blobs_removed/bytes_reclaimed, but the values array has them swapped so the zip pairs blobs_removed's name with the bytes value — confirming that mismatch too, with the load happening at metrics.rs:94. That's enough verification; time to write up the findings.
Findings, verified against the checked-out code:

🔴 `bug` services/proxy/src/sweep.rs:140: `forget(&index, &gone)` runs even when `dry_run` is true, so a "report only" dry run permanently deletes the index entries for every blob it would have removed — the blobs become unreachable cache misses and are collected as unreferenced garbage by the next real sweep, making `?dry_run=true` destructive despite the route's promise.

🔴 `bug` services/proxy/src/sweep.rs:102: `sort_by_key(|c| c.age)` sorts ascending, putting the *youngest* blobs first, so the eviction loop removes the most recently fetched blobs first — the exact opposite of the "Oldest first" comment and of the documented `CAIRN_CACHE_MAX_BYTES` behaviour; the hot working set is evicted while the stalest blobs survive.

🔴 `bug` services/proxy/src/sweep.rs:230: `clear_partials` unlinks every file in `incoming/` with no age check, but `BlobStore::temp_path` (store.rs:201) puts *live* in-flight downloads there; each sweep unlinks the temp files of concurrent fetches, whose `commit` rename (store.rs:259) then fails, so every sweep fails all downloads in flight at that moment.

🟠 `bug` services/proxy/src/metrics.rs:94: `values()` loads `sweep_bytes_reclaimed` at index 4 and `sweep_blobs_removed` at index 5, but `COUNTERS` puts `..._blobs_removed_total` at index 4 and `..._bytes_reclaimed_total` at index 5, so the two new counters are rendered under each other's names — the exact mix-up the comment above `COUNTERS` warns about, and the ops doc tells operators to alert on the misrendered `cairn_proxy_sweep_bytes_reclaimed_total`.

🟠 `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` takes (sweep.rs:83), so an admin-triggered sweep can run concurrently with the background sweep (or with another admin sweep) — the exact double-sweep over-eviction the module doc at sweep.rs:10-12 says the mutex exists to prevent.

🟠 `bug` services/proxy/src/sweep.rs:119: an unreferenced blob is removed with no `min_age` grace, but a blob is legitimately unreferenced in the window between `writer.commit()` (cache.rs:151) and `store.link` (cache.rs:163), which spans a registry round-trip; a sweep in that window deletes the freshly committed blob and the request 500s at cache.rs:90 ("a blob committed by this request is already missing").

🟠 `performance` services/proxy/src/sweep.rs:84: `run()` (and the admin handler via admin.rs:76) executes the fully synchronous walk-and-unlink `sweep()` directly on a tokio worker thread instead of `spawn_blocking`; the router comment in routes/mod.rs concedes a sweep "legitimately takes longer than ten seconds", so a large store blocks an async runtime worker for that whole time.

🟡 `bug` services/proxy/src/main.rs:108: `tokio::time::interval` completes its first tick immediately, so the first sweep runs at startup — the doc comment at lines 101-102 claims the first tick is one interval away precisely to avoid this; `interval_at(Instant::now() + period, period)` is what the comment describes.

🟡 `bug` services/proxy/src/sweep.rs:164: `fs::metadata` follows symlinks, so a link is counted at the size of its *target* (and a symlinked directory is recursed into and its contents unlinked), the inverse of the comment's claim that "a link is counted at the size of the link"; `symlink_metadata` is what the comment describes.

🔵 `bug` services/proxy/src/sweep.rs:134: when `fs::remove_file` fails on line 126, the blob is still counted in `removed`/`bytes`/`remaining` and pushed to `gone`, so the reported reclaim overstates reality and `forget` deletes the index entries of a blob that is still on disk, orphaning it until a later sweep.
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