sandbox:read-only (macOS Seatbelt)
-- reasoning --
Let me read the actual files under pr/ to check for defects.

Key areas to scrutinize:
1. `clear_partials` deletes everything in `incoming` without checking age or whether a fetch is currently in progress (BlobWriter writing). That would delete in-flight partial writes of active fetches. The doc says "A file in `incoming` is a fetch that is not coming back" — but an active fetch IS writing there. The sweep runs concurrently with fetches (background sweep interval). Clearing an in-progress fetch's temp file → fetch fails or worse: rename? Let me check store.rs for how the writer works.

2. `collect` uses `fs::metadata` which follows symlinks — the comment says a link is counted at the size of the link... but `fs::metadata` follows symlinks, returning the target's size and metadata, not the link's. To get link size you'd use `symlink_metadata`. So the comment contradicts the code: for a symlinked blob, `fs::metadata` gives target size and is_dir of target. Actually that might be intentional? Comment says "A link is counted at the size of the link and not of whatever it points at" — code uses fs::metadata which follows. Defect: comment/code mismatch; the size counted is target's. Actually is that a defect? If a store has hardlinks... hardlinks are just files, size is the same. Symlinks: metadata follows. So the comment claims something the code doesn't do. Hmm, but which behavior is correct? Counting symlink at target size is arguably right for space. The defect is the mismatch. Low/medium.

3. Also `clear_partials` deletes directory entries that might be directories? remove_file on dir fails, logged and continue — ok.

4. Concurrency: the sweep runs synchronously on the tokio runtime (std::fs in async context) — documented as deliberate. But `run()` holds a tokio Mutex across a synchronous blocking sweep... it blocks the executor thread. Documented tradeoff. But more importantly, the background sweep task calls `app.sweeper.run().await` which locks the mutex, then `self.sweep(false)` — blocking the async executor thread for the whole walk. Deliberate per docs. Not a defect per se? It blocks a worker thread on the multi-thread runtime; could starve. They documented it. Skip.

5. On-demand sweep route: `reclaim(&app, ...)` calls `app.sweeper.sweep(dry_run)` — note: this calls `sweep` directly, NOT `run()`, so it does NOT take the mutex! The one-at-a-time promise is kept by `run` holding the lock, but the admin route calls `sweep` directly, bypassing the lock. Two concurrent HTTP sweep requests, or a background sweep plus an admin sweep, run concurrently — exactly the interleaving the module doc says must not happen ("Two of them over one directory would each decide what to remove from a total the other is already changing"). That's a real bug: admin.rs `reclaim` should call `app.sweeper.run()` for non-dry-run, or sweep should take the lock. Line: in admin.rs, `let reclaimed = app.sweeper.sweep(dry_run);`.

Also blocking: admin route calls a synchronous, potentially long filesystem walk directly in the async handler → blocks the executor thread. And it's placed in the "untimed" router deliberately. But blocking the runtime... they documented the walk is synchronous deliberately. Still, calling blocking code in a handler without spawn_blocking is a defect arguably. But the background one has the same. Both documented. Hmm. The bigger one is the mutex bypass.

6. Race between sweep and active fetch: clear_partials deletes files in `incoming` while a BlobWriter may be writing to one. Check store.rs: writes go to temp file in incoming, then renamed. A sweep deleting the temp file mid-write: on Unix, the writer keeps the fd, writes succeed, then rename fails (file gone) → fetch fails. Worse: does the writer check rename success? Also, sweep then removes... the partial is deleted, writer's write to unlinked file — bytes vanish, rename fails with NotFound, blob not cached. Next request refetches. So consequence: active fetches get killed by sweep. Is there protection? clear_partials doesn't check age at all — no min_age grace, deletes files that were just created a millisecond ago. Defect: clear_partials removes in-progress fetch temp files with no age check, unlike blobs which get min_age. Check store.rs to confirm the temp file lives in `incoming` during fetch. Let me read store.rs.

7. `forget(&index, &gone)`: index map was built at sweep start; deletes index entries for digests removed. But wait — the index entries for removed digests... For blobs removed because unreferenced, index.get(hex) is empty anyway. For ceiling-evicted blobs, entries removed. OK. But race: between collecting index and removing, a fetch might have just resolved an entry and be... fine.

Bigger race: a concurrent fetch that just renamed a blob into place and wrote the index entry — sweep's index snapshot doesn't include it, so sweep sees blob as unreferenced → deletes it immediately (no min_age for unreferenced!). The age comment says "Age does not enter into the first" — a blob no index entry names cannot be reached. But it CAN be reached a microsecond later when the index write completes. Race: fetch completes (blob renamed in, index entry being written) while sweep runs → sweep reads index without the new entry → deletes the just-stored blob. Next request refetches — safe but wasteful, and could ping-pong. Is it a defect worth reporting? It's a TOCTOU between index snapshot and blob listing. Consequence: recently stored blob deleted, refetch. Low severity maybe. Actually could also delete index entry? No — forget uses the old index map, the new entry's path isn't in it. So blob deleted, index entry remains, next request resolves entry → miss → refetch. Safe but thrash. Low.

8. `scanned` counts candidates; `held` sums candidate sizes. Fine.

9. metrics.rs: `values()` returns sweep_bytes_reclaimed then sweep_blobs_removed — order matches COUNTERS order? COUNTERS: hits, misses, upstream_failures, policy_refusals, sweep_blobs_removed_total, sweep_bytes_reclaimed_total. values(): ..., sweep_bytes_reclaimed, sweep_blobs_removed. MISMATCH! The doc comment says "Name and help for each counter, in the order [`Metrics::values`] reads them. Keeping the two side by side is what stops a fifth counter from being rendered under a fourth one's name." values() has bytes before blobs, COUNTERS has blobs before bytes. So bytes counter rendered under blobs' name and vice versa. That's a real bug — metrics mislabeled. Check the render code in metrics.rs to confirm it zips COUNTERS with values().

10. `Duration::from_hours` / `Duration::from_mins` — std Duration doesn't have these (they're in the unstable std or in `jiff`/`humantime`?). Wait, config.rs uses `Duration::from_hours(1)` — std::time::Duration has from_secs, from_millis; from_hours is unstable (duration_consts? no — `Duration::from_hours` is unstable feature `duration_consts`? Actually it's `duration_ext`? There's an unstable `Duration::from_hours`? I recall `Duration::from_hours`/`from_mins` are unstable (feature `duration_consts`, RFC). Not stable as of Rust 1.8x. So this wouldn't compile unless they have a custom Duration or use a different crate. In config.rs, what Duration is imported? Check the file. If `std::time::Duration`, it's a compile error. Maybe they define parse_duration returning their own? Let me read config.rs.

11. config validation: cache_min_age has no validation — zero allowed. min_age zero means grace period gone; is that a problem? Not necessarily a defect. But also: no check that cache_max_bytes >= ... whatever. Fine.

12. routes/mod.rs: sweep route outside timeout — fine, documented. But sweep route in untimed router — also admin purge remains in bounded. OK.

13. `RequestId` extractor — check it's imported in admin.rs. The diff shows `RequestId(request_id): RequestId` used; diff doesn't show an import for RequestId. The existing admin.rs `purge` presumably uses it. Check.

14. main.rs spawn_sweeps: `tracing::info!(?reclaimed, ...)` — Reclaimed derives Debug, fine.

15. MissedTickBehavior::Delay: comment says "The next one starts a full interval after this one finished." Actually Delay behavior: ticks at now + period after a missed tick. With Delay, the next tick is period after the delayed tick — approximately correct. Fine.

16. `reclaim` in admin: also records metrics for non-dry-run — fine. But logging info with dry_run=false duplicates background. Fine.

17. dry_run route: dry run still calls clear_partials with dry_run=true — doesn't remove. But it calls `referenced` and full collect — fine.

Wait — dry_run=true in admin route calls `app.sweeper.sweep(dry_run)` directly, again bypassing mutex — but also a dry run concurrent with a real sweep reads a half-changed state; minor.

Also: dry run via route doesn't take the lock but the blocking walk happens in the handler thread — same as #5.

18. `collect` on blobs dir: blobs dir structure "blobs/sha256" — recursive collect handles subdirs. Fine.

19. `age_of` returns Duration::default() (zero) on failure — a blob with future mtime gets age 0, treated as newest, kept longer. Fine/intentional.

20. `clear_partials` — also removes files currently being written by BlobWriter. Need to check store.rs: does the writer write into `incoming`? The store docs say "Writes go to a temporary file and are renamed into place" — temp presumably in incoming. If so, background sweep every 15m deletes in-flight fetch temp files → active fetches fail (rename fails). That's a real bug: clear_partials has no age threshold, unlike blobs. Severity: high? The fetch fails, client gets error, refetch. Under load, sweep can kill many concurrent downloads. I'd say orange.

Also possible worse: writer's write continues to unlinked inode, then rename fails... check store.rs for error handling — maybe the writer errors and the request 500s. Or maybe writer uses File created then rename; if file removed mid-write, `fs::rename` fails NotFound → fetch fails. Either way fetch killed.

21. Also sweep deletes blob files while a reader is streaming one (cache::serve reading the file). On Unix unlink while reading is fine — reader keeps fd. But the request may have been served... the content already read? If serve opens the file then reads, unlink mid-read is fine on Unix. OK.

22. `forget` removes index entries for gone digests — but includes digests removed as "unreferenced" (index.get empty, no-op) — fine. But note: `gone` includes hex for every removed candidate, including ones where remove_file failed (purged concurrently). forget then removes index entries for those — if a purge removed blob but another request refetched the blob (new blob file, same digest) between collect and forget, forget would delete index entries pointing at a still-existing blob. Next request: index miss → refetch. Harmless-ish. Skip or low.

23. metrics doc: "The four counters" changed to six — fine.

24. Check `values()` mismatch carefully — need to read metrics.rs render function.

25. config.rs: check `parse_duration` exists and Duration import. Also `Duration::from_mins` — not std. Let me check whether config.rs defines its own Duration type or imports something. Read the file.

26. routes/mod.rs removed the doc comment about cache route but moved it — fine.

27. `spawn_sweeps(app.clone())` — App is Arc<...>, Shared = Arc<App>. Sweeper holds Mutex. Fine.

28. Admin sweep route: no RequestId plumbing issue? `error.into_response_with(request_id.as_deref())` — matches purge presumably.

29. In admin.rs, does `Query` extractor + `Json` imports conflict? routes/mod.rs also imports axum::Json — different module. Fine.

30. The sweep route returns Json(reclaimed) 200 even when dry_run removed nothing — fine.

31. Potential: `sweep` is `&self` sync fn called from async — blocking. Combined with it being in "untimed" router... the walk could take minutes; during that, a tokio worker thread is blocked. With multi-thread runtime and few threads, this can stall the whole proxy including heartbeats. They documented the choice for the background task but doing it inline in an HTTP handler also blocks. Actually wait — the background task does `app.sweeper.run().await` which locks then calls the blocking `self.sweep(false)` on the async task — blocking a runtime worker thread for the whole sweep. Documented as deliberate ("The walk is synchronous"). Hmm, deliberate. I'll not report, or report low. The mutex bypass is the clear bug.

Let me now read the actual files to confirm: metrics.rs render, config.rs Duration, store.rs (incoming, IndexEntry, resolve behavior, purge), admin.rs imports.
I'll read the changed files under `pr/` to verify each diff hunk against the real code.
└ 2994 tok · 103.1 tok/s · 12K ctx · 1817ms ttft · 29.0s wall
↳ read_file: read pr/services/proxy/src/metrics.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/store.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/routes/admin.rs
└ read_file: read complete
auto-compress is on at 85% but the context window of "z-ai/glm-5.3-flash" on openrouter is unknown, so this run will not compress - set AFI_SOURCE_OPENROUTER_CONTEXT_WINDOW (or pass --context-window) to enable it
-- reasoning --
Key findings so far:

1. Metrics mismatch: COUNTERS order is [..., sweep_blobs_removed_total, sweep_bytes_reclaimed_total] (blobs first, bytes second) but `values()` returns sweep_bytes_reclaimed first, then sweep_blobs_removed. So names/values are misaligned — bytes value rendered under blobs_removed name. That's a real bug at metrics.rs:94-95 vs COUNTERS order at 51-56. Confirmed.

2. sweep.rs `run()` takes the Mutex then calls self.sweep(false) — synchronous blocking work inside async context. The module doc says the walk is synchronous deliberately (std fs calls) — that's documented as deliberate. But it blocks the async runtime thread; the doc says it's deliberate. Hmm, but the mutex is a tokio Mutex held across a blocking sync call — the on-demand route calls `app.sweeper.sweep(dry_run)` directly WITHOUT acquiring the mutex! The doc claims "one-at-a-time promise is something the type keeps" but `sweep()` is public and admin route calls `sweep()` directly, not `run()`. So a manual sweep can run concurrently with a background sweep — the one-at-a-time invariant is broken. admin.rs:76 calls `app.sweeper.sweep(dry_run)` while the mutex is only in `run()`. That's a real bug: concurrent sweeps both compute totals and could over-evict. Also dry_run doesn't take the lock but that's fine. Actually the fix: `reclaim` should call run() when !dry_run, or sweep() should lock internally. Bug in sweep.rs (Sweeper::sweep / run) and admin.rs:76.

3. Blocking sync I/O on the async executor: the sweep route handler `reclaim` runs the entire synchronous walk inside an async handler — blocking a tokio worker thread for potentially minutes (doc says a sweep of a large store legitimately takes longer than ten seconds; the route is placed outside timeout for that reason). Blocking the runtime thread while holding it — with multi-thread runtime, other requests continue on other threads, but a full runtime with few workers... It's documented as deliberate in sweep.rs doc ("The walk is synchronous"). But running it inside a request handler on the async runtime is different from the interval task. Actually both run on the runtime. Hmm. The documented deliberate choice is std fs vs tokio fs. Blocking an executor thread for minutes is a real concern but the code documents it. I'd flag as medium: blocking call in async handler can stall the worker thread; but they justify. Perhaps flag the lock issue instead which is unambiguous.

4. `age_of` uses modified time; fine.

5. `collect` uses fs::metadata which follows symlinks — comment says "A link is counted at the size of the link" but `fs::metadata` follows symlinks and returns target metadata (so size of the target, not the link). The comment claims symlink_metadata behavior. Actually for a symlink, `fs::metadata` follows it, giving target's size. So the comment is wrong and a symlink to a huge file is counted at target size. Also a broken symlink: fs::metadata fails, skipped — fine. But deeper: a symlinked blob pointing at an external file would be counted at the target's size (contradicting the comment) — worse, if symlink target is a directory, collect recurses into it (following symlinks → potential infinite loop for a symlink cycle). fs::metadata on symlink-to-dir returns is_dir true, then recursion — a symlink loop (dir pointing to ancestor) = infinite recursion and stack overflow. That's a defect: use symlink_metadata. Severity: low/medium since symlinks are unusual but the code explicitly claims to handle them. I'd flag: collect uses fs::metadata (follows symlinks) contradicting the comment, counting the target's size and recursing into symlinked dirs — a symlink cycle recurses until stack overflow. Medium/blue.

6. `scanned` count uses u64::try_from... fine.

7. In sweep(), removal condition: `remaining >= self.max_bytes` — remaining is total held; if held > max, remove oldest. But it removes blobs until remaining < max, but it also removes unreferenced blobs regardless of age — fine per doc.

Wait: subtle bug — when `!index.contains_key(hex)` the blob is removed but the sweep continues; but consider min_age: for ceiling removal, once remaining < max_bytes the loop continues but `remove` false → continue. Fine.

8. `forget` removes index entries for removed digests. But if the same digest is shared by index entries, fine. However: forget removes index entries for blobs removed — but in a dry run, `gone` includes everything that would be removed, and `forget` is called with dry_run?! Look: in sweep(), `if !dry_run { fs::remove_file... }`, then after loop `forget(&index, &gone)` is called unconditionally — including in dry_run! `forget` does real fs::remove_file on index entries regardless of dry_run. That's a serious bug: a dry run deletes the index entries, breaking the cache (entries name blobs still present — but the sweep would have removed those blobs in a real run... in dry run no blob was removed, yet index entries get deleted). Result: dry run destroys index entries, and worse the "reports what one would reclaim without removing anything" promise broken. Line: sweep.rs forget call — let me get line numbers.

9. main.rs spawn_sweeps: `tracing::info!(?reclaimed, ...)` — Reclaimed derives Debug, fine.

10. MissedTickBehavior::Delay with interval: first tick immediate? tokio interval first tick completes immediately! `tokio::time::interval` — "The first tick completes immediately". So the comment "The first tick is one interval away" is wrong — sweep runs immediately at startup. Consequence is minor (sweeps empty store). Not a big defect; doc/comment mismatch. Maybe blue severity. Actually the consequence: a proxy that just started sweeps a cache it hasn't begun to fill — harmless. But it also means the interval is anchored at start, subsequent ticks at interval. Low.

11. routes/mod.rs: the sweep route placed in untimed router — but the timeout layer... sweep route previously commented said cache route outside timeout. Fine.

12. config.rs: no validation that cache_min_age — no check, fine (zero min_age allowed, removes immediately; acceptable? min_age zero means everything evictable; not validated but arguably intended... no check but that's operator choice). Also DEFAULT_CACHE_MAX_BYTES 32GiB fine.

13. `clear_partials` in a dry run: not counted toward `removed`/`bytes` (partials counted separately) fine. But dry_run returns partials count without removing — good. However in dry_run, clear_partials counts entries as removed without checking they're removable... fine.

14. Held bytes: `held` computed only from blobs; the sweep removes partials too but partial bytes not counted in bytes — documented "Blobs only".

15. Error in `collect` over index dir: `referenced` calls collect which uses fs::metadata and recurses; index entries are files. Fine.

16. Race: sweep removes blobs while a fetch is streaming from one? Blob being served is open; unlink fine on unix.

17. Race between sweep deciding and BlobWriter commit: a blob committed during sweep not in candidates — fine.

18. Important: sweep removes unreferenced blobs even during a concurrent fetch that just committed blob but not yet linked the index! Sequence: miss → fetch → commit blob (blob now on disk, index not yet linked). Sweep runs between commit and link: blob not in index → removed. Then link writes index entry pointing at a gone blob. Next request: resolve hits index, open_blob fails → miss → refetch. One wasted fetch, consistent with purge behavior ("stale entry costs a single refetch"). Not a bug beyond documented.

19. metrics.rs: also note the render doc "twenty lines" fine.

20. main.rs: `spawn_sweeps(app.clone())` before serve — fine. On shutdown, task dropped — documented.

21. admin.rs `reclaim` is a sync fn doing the whole sweep inside async handler `sweep` — blocking executor. Also the sweep route lacks timeout deliberately... but handler blocking a runtime thread while a Mutex-free concurrent sweep... The lock bug stands.

Also: sweep route is POST /v1/admin/cache/sweep — matches docs.

22. `held` excludes partial bytes but the ceiling is enforced only on blobs — documented.

23. In `sweep`, when a blob fails to be removed (fs error, e.g. permission), the code still counts it as removed and subtracts bytes — `remaining` decremented and counters incremented even though the file is still there. Consequence: metrics overcount and the ceiling computed wrong next sweep (fine, next sweep recomputes). But reported `removed`/`bytes`/Json response claims bytes reclaimed that weren't, and the index entries for that blob get deleted by `forget` even though the blob remains — leaving a blob on disk with no index entry, so the NEXT sweep will remove it via the unreferenced path... which actually works out, but the response lies. Moderate. Flag as 🟡: removal error still counted as reclaimed (sweep.rs lines around the remove_file err). Line numbers needed.

24. Also, `scanned` etc. Let me read sweep.rs and main.rs and routes/mod.rs for actual line numbers.
Now let me read the remaining changed files with real line numbers.
└ 2086 tok · 111.0 tok/s · 24K ctx · 1204ms ttft · 18.8s wall
↳ read_file: read pr/services/proxy/src/sweep.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/main.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/routes/mod.rs
└ read_file: read complete
-- reasoning --
Now let me analyze for defects.

Key candidates:

1. **Metrics COUNTERS order vs values order mismatch** — COUNTERS order: cache_hits, cache_misses, upstream_failures, policy_refusals, **sweep_blobs_removed**, **sweep_bytes_reclaimed**. values() returns: hits, misses, failures, refusals, **sweep_bytes_reclaimed**, **sweep_blobs_removed**. So bytes get rendered under `cairn_proxy_sweep_blobs_removed_total` and vice versa. That's a real bug — labels swapped. metrics.rs:51-57 vs 88-97. Doc comment at line 30 says "in the order values reads them" — so it's a bug. 🔴/🟠. Severity: metrics mislabeled — ops monitoring wrong. 🟠 high.

Also docs reference `cairn_proxy_sweep_bytes_reclaimed_total` — operator would read the blobs counter. Confirmed high.

2. **`sweep` route runs blocking synchronous work in async handler on the runtime thread** — `admin::sweep` calls `app.sweeper.sweep(dry_run)` which is fully synchronous `std::fs` walk of potentially 65k directories — blocking an async executor thread. The module doc itself argues synchronous is fine vs tokio::fs, but calling it from an async handler blocks a worker thread for potentially a long time (a large store could take minutes). That starves other requests including the runtime. Severity: performance. Also `Sweeper::run` (background) does the same blocking call inside async task. This is arguably a deliberate design choice per the comment... but blocking the executor thread from the HTTP handler is still a defect. 🟠 performance. Actually the doc comment only addresses the choice of sync fs vs tokio::fs, not running it on a runtime worker. Calling blocking code in async context without spawn_blocking is a genuine defect. Also note mutex is a tokio Mutex held across the blocking call — fine.

3. **Race between sweep and the serve path / fetch**: sweep removes a blob that's referenced? No — referenced blobs are only removed when over ceiling and old enough; that's intended. But there's a race: sweep reads index, then decides a blob is unreferenced and deletes it — meanwhile a fetch just committed a new blob... not really a defect to point to.

4. **`clear_partials` deletes in-progress fetches**: `incoming` holds temp files of *actively running* fetches (BlobWriter writes into incoming). A sweep unconditionally removes every file in `incoming` — including partial writes of fetches currently in progress! The doc says "A file in `incoming` is a fetch that is not coming back" — false: an active download writes there for the whole duration of a 200 MiB fetch (up to fetch_timeout 30s... actually max artifact 256MiB with fetch timeout 30s). A concurrent fetch's temp file would be unlinked mid-write; the writer keeps writing to the unlinked inode, then commit's rename fails with NotFound → fetch fails. Worse, on Linux rename of unlinked file fails. So a background sweep every 15m can kill in-flight downloads. That's a real bug: no age check on partials, unlike blobs. 🔴? The window is fetch duration; sweeps every 15m; probability moderate. I'd call it 🟠 bug: sweep deletes in-flight fetch temp files causing commit failure. Line sweep.rs:91 / 230-235.

Also dry_run counts partials it would remove including active ones — consistent.

5. **`forget` deletes index entries for blobs removed while store was at/below ceiling?** forget deletes index entries naming digests removed. But wait: blobs removed for being unreferenced — index doesn't contain them (contains_key false), so forget does nothing for those (get returns None). Fine.

But subtle bug: blob removed because `!index.contains_key(hex)` — hex from file_name. If blob filename isn't a valid... it's fine.

6. **Index entries removed while `BlobStore::resolve` may be reading** — rename-based writes make that atomic; remove of index entry during a fetch that's about to link... minor.

7. **`sweep` route with dry_run bypasses... no.

8. **Double-counting metrics**: admin sweep and background sweep both call record_sweep — fine, sweeps are separate events.

9. **Route conflict**: `/v1/admin/cache/sweep` POST vs `/v1/admin/cache/{digest}` DELETE — different methods, no conflict.

10. **Query deserialization: `?dry_run=true`** — bool serde parses "true" fine. `?dry_run=1` errors → 400 via rejection? Query extractor rejection returns error response not going through error handler — minor, default axum rejection. Fine.

11. **`spawn_sweeps` task not tracked/aborted** — documented as deliberate.

12. **Cache route untimed + sweep untimed: comment moved** — fine.

13. **`age_of` returns 0 for future timestamps** — meaning age 0 < min_age, so blob protected. Actually a blob with future mtime gets age 0, treated as brand new — conservative, fine. But `meta.modified()` error also → age 0, protected. Documented as flattening. Hmm, actually flatten to 0 means it will NOT be removed (age 0 < min_age) unless unreferenced. That's safe-side. Fine.

14. **`remaining >= self.max_bytes` check**: if held already below max, nothing evicted by ceiling — fine. But when store is over ceiling and candidates are all too young (age < min_age), nothing is removed and store stays over ceiling — documented behavior in docs ("everything in the store is either referenced or inside its grace period"). Fine.

15. **`held` includes only blobs, but ceiling compares against blobs only** — fine, documented.

16. **`collect` follows symlinks?** `fs::metadata` follows symlinks (vs symlink_metadata). Comment says "A link is counted at the size of the link" — but `fs::metadata` follows the symlink and returns the target's metadata, so size is the target's size, not the link's. Also a symlinked directory would be recursed into (meta.is_dir() true for symlink to dir) — potential infinite loop if cyclic symlinks. The comment claims link counted at link size, which is what `symlink_metadata` would do. So the code contradicts its comment: should use `fs::symlink_metadata`. Consequence: symlink to huge file counts full size (overcounting) or symlink cycle → infinite recursion/stack overflow. 🟡/🟠. Actually is this a real defect? `fs::metadata` follows symlinks; comment claims it doesn't. Also symlink loop → infinite recursion. I'd report 🟡.

17. **`Digest::parse` & hex()** — need to check digest.rs quickly? The referenced map keyed on `digest.hex()`, and blob filenames are hex from digest.hex(). Fine.

18. **Index referenced map: index entries for digests whose blob doesn't exist** — index.contains_key(hex) true, blob protected even though blob... blob exists since candidates come from disk. Fine.

19. **`forget` in dry_run**: dry_run doesn't remove blobs but `forget` is still called unconditionally at line 140 — in a dry run, `gone` contains blobs it *would* remove, and `forget` deletes the index entries for them! That means a dry run destroys index entries for blobs that still exist — making cached coordinates miss and refetch. That's a real bug: `forget` should be skipped when dry_run. Line 140. Severity 🟠/🔴. Dry run is documented "reports what one would reclaim without removing anything" — but it removes index entries, breaking the cache for those coordinates (subsequent resolve = miss, refetch, re-link — data isn't lost but the promised "without removing anything" is broken and it churns the cache). Also an operator trying a new ceiling via dry run would wipe index entries. 🟠.

Wait — check: `sweep(dry_run=true)` → loop computes remove decisions, doesn't remove files, but pushes to `gone`. Then `forget(&index, &gone)` deletes index entry files unconditionally. Yes. Bug at sweep.rs:140 (and the route docs). Severity: high — dry run mutates state. 🟠 (data loss? index entries only, refetch recovers; but violates dry run promise and could delete index entries for blobs being actively served... a serve reads index then opens blob; if index removed mid-serve it's fine). 🟠.

20. **Race: sweep deletes index entries while a concurrent `link` writes them** — inherent.

21. **`reclaim` runs blocking on runtime** — mentioned above.

22. **Metrics: `record_sweep` counters rendered under swapped names** — main bug #1.

23. **`held` double counts hard links** — nah.

24. **`routes/mod.rs` comment removal about timeout**: fine.

25. **`.env.example` values fine.**

26. **`config.rs`: `Duration::from_hours` / `from_mins`** — these are unstable std methods (`Duration::from_minutes`? Actually `Duration::from_hours` is unstable nightly feature `duration_constructors`). But existing tests use `Duration::from_mins(2)` and `Duration::from_hours(1)` in test at line 350-351 — pre-existing. So presumably the codebase has an extension or uses a newer Rust... Not our diff's concern; and tests already used them. Skip.

27. **sweep_interval validation: cache_min_age not validated** (zero min_age allowed — evicts immediately anything when over ceiling; acceptable).

28. **Background sweep first tick one interval away**: `interval` first tick completes immediately! tokio's `interval` first `tick()` returns immediately. The doc comment claims "The first tick is one interval away, which is what keeps a proxy that has only just started from sweeping a cache it has not begun to fill." That's wrong — `tokio::time::interval` fires the first tick immediately. So a proxy that has just started sweeps a cache it has not begun to fill — exactly what the comment says it prevents. Consequence: mostly harmless (empty store), but the doc claim is wrong and a startup sweep runs immediately. Also combined with clear_partials: a just-started proxy... incoming would be empty right after start. Low impact. Still, the stated invariant is false. 🔵/🟡. It's a real behavior-vs-comment defect. Consequence minor (an immediate sweep on startup). I'd report 🔵 or 🟡. I'll say 🟡 medium? The consequence: at startup, an immediate sweep runs; with the partials bug, could delete in-flight fetches... at startup nothing in-flight. Low. 🔵.

Actually wait — is it immediate? tokio::time::interval: "An interval will tick indefinitely. At any time, the Interval value can be dropped. ... The first tick completes immediately." Yes, documented. So bug.

29. **MissedTickBehavior::Delay with comment "next one starts a full interval after this one finished"** — Delay behavior: ticks are delayed the same amount... Delay means the tick is delayed by the missed duration? Actually Delay: "the next tick is at the scheduled time plus the interval"... MissedTickBehavior::Delay: ticks are rescheduled so that the next tick occurs at `last_tick + period` where last_tick updated to the time when tick was called... Effectively the next tick is a full period after the delayed tick returns. Comment is fine-ish.

30. **`clear_partials` counts directory entries — incoming could contain subdirs? No.**

31. **Metrics doc comment "The exposition below is twenty lines"** — nit, skip.

32. **admin.rs: sweep route placed in untimed router — but blocking sync in handler means no timeout, and Tokio worker blocked** — covered.

33. **`Sweeper::run` holds tokio Mutex across blocking sync code — the background loop is fine.

34. **Security: dry_run response includes... fine.

35. **The sweep route's blocking work in the async handler also means the request-id echo... fine.

36. **`forget` removing index entries for blobs that failed to remove**: if `fs::remove_file` of the blob fails (line 126-131), the code still counts it as removed, adds to `gone`, and `forget` deletes the index entries — leaving a blob on disk with no index entry. Then next sweep will see it unreferenced and try again — self-healing. But also `bytes` counted and `remaining` decremented for a blob that wasn't removed → the sweep believes it reclaimed bytes it didn't; the store stays over the ceiling while counters claim success. Minor accuracy bug. Also, on failure the blob file remains but index gone → resolve misses → refetch → link rewrites index → fine. 🟡? It's an edge: remove fails usually because already gone. If remove failed because of EPERM, we'd count reclaimed bytes that remain on disk and delete index entries. Also `removed` counter incremented. Medium-low. I'd report 🔵/🟡. Hmm, worth including as 🟡? The consequence is metrics/report inaccuracy when unlink fails. I'll include as 🟡 maybe. Keep it — it's concrete: line 125-137.

Actually more important variant: since remove failure is usually NotFound (already gone), counting it as removed is arguably fine. I'll include as blue.

37. **`referenced` reads index entries via `collect` which uses `fs::metadata` and treats dirs recursively — fine.

38. **`scanned` counts blobs only, fine.

39. **Concurrency: admin sweep (sync fn, no lock!)** — `reclaim` calls `app.sweeper.sweep(dry_run)` directly, NOT `run()`. The mutex `running` is only taken in `run()`. So an on-demand sweep does not take the lock: it runs concurrently with the background sweep — violating the module's "One sweep at a time" promise and the type's doc "Held for the whole of a sweep, so this module's one-at-a-time promise is something the type keeps rather than something every caller remembers." admin.rs:76 calls `app.sweeper.sweep(dry_run)` instead of going through the lock. Two concurrent sweeps over the same directory → double deletion accounting, over-eviction below the ceiling. That's a real bug: 🟠/🔴. The design intent explicitly stated in sweep.rs:10-12 and 65-67 — the caller (admin.rs:76) bypasses it. For dry_run concurrent with a real sweep it's just inaccurate reporting; for a real on-demand sweep concurrent with the background sweep it's the exact hazard described. 🟠.

40. **`Query<SweepQuery>` with `dry_run` bool: `?dry_run=xyz` → rejection 400 with axum's default body, not the JSON error format — minor, skip.

41. **`.env.example` sweep interval vs metrics scrape comment fine.

42. **docs claim `POST /v1/admin/cache/sweep` takes bearer token — matches.

43. **routes/mod.rs: the sweep route untimed means it can hang forever holding... fine.

44. **`collect` recursion depth on deeply nested index dirs (ecosystem/name/version/file) — bounded.

45. **`age_of` uses `modified()` not `accessed()` — LRU by mtime; a blob served many times isn't touched → old but hot blobs evicted. Design choice; skip? Could argue "cache min age by modification, but hot blobs get evicted while cold ones... " no, mtime works for LRU-ish. Skip.

46. **Ceiling check `remaining >= self.max_bytes`**: compares blob-bytes to ceiling but held was computed after partials cleared — fine.

47. **Mutex fairness: background and admin sweeps could interleave... covered by #39.

Also #4: clear_partials removing active fetch temp files. Verify: BlobWriter writes to `incoming/<pid>-<seq>` while download in progress (could be up to fetch_timeout = 30s... actually fetch timeout 30s limits fetch duration, so window ≤30s per fetch; sweeps every 15m → collision probability low but nonzero; with many concurrent fetches, decent). The unlink succeeds on POSIX while the fd is open; commit then renames the path → NotFound error → fetch fails, client gets error, and the bytes are lost (must refetch). Real bug: sweep should skip partials younger than some age (or at least min_age). Severity 🟠.

Also `BlobWriter::commit` — rename of unlinked temp fails → error propagates → 502 for client. Also `Drop` then tries remove → debug warn. Fine.

Let me also check digest.rs quickly for `hex()` and parse? Probably fine, skip.

Check whether `Duration::from_hours`/`from_mins` exist — they're unstable std (`duration_constructors`)? Actually `Duration::from_hours` etc. landed in Rust 1.87? Let me recall: `Duration::from_weeks`, `from_days`, `from_hours`, `from_mins`, `from_secs_f16`... The `duration_constructors` feature — from_hours/from_minutes/from_mins? I believe `Duration::from_hours` was stabilized in Rust 1.87 (2025) along with from_days/from_mins... Actually stabilized: `Duration::from_weeks`? Hmm. In Rust 1.87.0 (May 2025): "stabilized `Duration::from_weeks`... " I'm not sure. The tests already use `Duration::from_mins` in existing code (test at line 350 pre-existing), so it compiles in their toolchain. Skip.

Also `metrics.rs` doc line 30-32: "Keeping the two side by side is what stops a fifth counter from being rendered under a fourth one's name" — ironic given the swap.

Also check `.env.example` — CAIRN_CACHE_MIN_AGE=1h parse ok.

Now severity assignment:

- 🔴 metrics.rs: values()/COUNTERS order mismatch — bytes rendered under blobs-removed name and vice versa. Ops alert on `cairn_proxy_sweep_bytes_reclaimed_total` reads the blob count. I'd say 🟠 (high, monitoring broken but not data loss). Given docs/operations.md tells operators to watch that exact counter, high is right.

- 🔴/🟠 admin.rs:76 on-demand sweep bypasses the one-at-a-time mutex → concurrent sweeps with background sweeper → over-eviction/double accounting. 🟠.

- 🟠 admin.rs:76 / sweep.rs:90 blocking synchronous filesystem walk of the whole store executed directly on the async runtime worker thread — stalls all other requests (and the metrics/health probes) for the duration of a large sweep. 🟠 performance. Note background task also blocks a worker thread but that's the documented tradeoff; the route doing it is worse. I'll report once, pointing at admin.rs:76 (and mention sweep.rs:90). Actually where to point? The defect: `Sweeper::sweep` is sync and does full blocking walk; called from async handler. Point at admin.rs:76.

- 🟠 sweep.rs:140 `forget` runs on dry run — deletes index entries for blobs it only reported. 🟠.

- 🟠 sweep.rs:91/230 clear_partials deletes in-flight fetch temp files (no age guard), killing concurrent downloads whose commit then fails. 🟠.

- 🔵 sweep.rs:164 `fs::metadata` follows symlinks, contradicting comment (link counted at target size; symlinked dir recursed, cycle risk). 🟡 maybe. Consequence: a symlink to a huge file inflates `held` and gets evicted... plus recursion loop. I'd say 🟡.

- 🔵 main.rs:115 first `interval` tick fires immediately, contradicting doc that startup sweep is delayed one interval. 🔵.

- 🔵 sweep.rs:126-137 blob whose unlink fails is still counted as removed/reclaimed and its index entries deleted. 🔵.

- config.rs: no validation that cache_min_age... skip. Also no validation sweep_interval vs... skip.

One more: `SweepQuery` dry_run — a GET/POST without query defaults false → runs real sweep, fine.

Also check: `referenced` uses `collect` on INDEX dir; index entries are files; fine.

Also: `held` includes all files under blobs/sha256 including non-blob files — fine.

Also `routes/mod.rs` line 131: sweep route in `untimed` — a slow sweep holds... covered by blocking issue.

Potential double-count: background sweep calls record_sweep, and admin real sweep calls record_sweep — both legit.

Let me also double check the COUNTERS/values mismatch is real: COUNTERS index 4 = "cairn_proxy_sweep_blobs_removed_total", index 5 = "cairn_proxy_sweep_bytes_reclaimed_total". values(): [.., sweep_bytes_reclaimed, sweep_blobs_removed]. zip pairs name #4 (blobs_removed) with value bytes_reclaimed. Yes, swapped. Confirmed.

Should I check digest.rs / cache.rs for anything about the sweep interacting? The serve path: cache::serve resolves index → opens blob. Sweep could delete blob between → open fails → treated as miss → refetch. Fine by design.

One more: `Sweeper::run` returns after lock; `spawn_sweeps` awaits run then records — fine.

Order the findings by severity. Format lines exactly.
Findings from reading the changed files under `pr/`:

🔴 `bug` services/proxy/src/metrics.rs:88: `values()` returns `sweep_bytes_reclaimed` then `sweep_blobs_removed` (lines 94-95), but `COUNTERS` lists `cairn_proxy_sweep_blobs_removed_total` then `cairn_proxy_sweep_bytes_reclaimed_total` (lines 51-57) — `render()`'s zip pairs each counter with the other's name, so every scrape reports bytes under the blobs-removed metric and vice versa. `docs/operations.md` tells operators to watch `cairn_proxy_sweep_bytes_reclaimed_total`, which now shows a blob count.

🟠 `bug` services/proxy/src/routes/admin.rs:76: `reclaim` calls `app.sweeper.sweep(dry_run)` directly, bypassing the `running` mutex that only `Sweeper::run` (sweep.rs:82-85) takes. An on-demand sweep therefore runs concurrently with the background sweep, which is exactly the two-sweeps-over-one-directory hazard sweep.rs:10-12 says the type exists to prevent: both decide what to remove from a total the other is changing, over-evicting the store far below the ceiling.

🟠 `bug` services/proxy/src/routes/admin.rs:76: the sweep handler runs `Sweeper::sweep` — a fully synchronous `std::fs` walk and unlink pass over the whole store (sweep.rs:90-149) — directly on the async runtime worker thread. A store with tens of thousands of entries blocks the executor for the whole pass, stalling every other request including `/healthz` and `/metrics`; it needs `spawn_blocking`.

🟠 `bug` services/proxy/src/sweep.rs:140: `forget(&index, &gone)` runs unconditionally, including on a dry run. `gone` holds every candidate the dry run *would* remove, so `?dry_run=true` — documented as reporting "without removing anything" — actually deletes the index entries for those blobs, turning live cache coordinates into misses and forcing refetches for an operator who was only trying a ceiling out.

🟠 `bug` services/proxy/src/sweep.rs:230: `clear_partials` unlinks every file in `incoming` with no age check, but `incoming` also holds the temp files of fetches in flight right now (`BlobStore::writer`, store.rs:171-180, writes there until commit). A sweep that lands mid-download unlinks the temp file out from under the writer; the later `fs::rename` in `BlobWriter::commit` (store.rs:259) fails with NotFound and the client's fetch fails. Needs the same `min_age` grace the blob path has.

🟡 `bug` services/proxy/src/sweep.rs:164: `fs::metadata` follows symlinks, so a symlink is counted (and recursed) at its *target's* size and type, not the link's — the opposite of what the comment at lines 160-163 claims (`symlink_metadata` is what that needs). A symlinked directory is also recursed into, so a symlink cycle under the blob dir makes `collect` recurse until the stack blows.

🔵 `bug` services/proxy/src/main.rs:115: tokio's `interval` completes its first tick immediately, so the loop sweeps straight away. The doc comment at main.rs:101-102 claims the first tick is one interval away precisely to stop a freshly started proxy from sweeping an empty cache — the stated behaviour and the actual behaviour are opposite (harmless today only because the store is empty at startup).

🔵 `bug` services/proxy/src/sweep.rs:126: when `fs::remove_file` fails, the blob is still counted — `remaining` is decremented, `bytes`/`removed` incremented (lines 134-136) — and `forget` then deletes its index entries anyway. A sweep that cannot unlink (permissions, EBUSY) reports reclaimed bytes that are still on disk and leaves blobs on disk that nothing in the index can reach.
└ 5558 tok · 106.5 tok/s · 31K ctx · 1405ms ttft · 52.2s wall