sandbox:read-only (macOS Seatbelt)
-- reasoning --
Let me review the diff. Need to check files under pr/. Key areas: metrics order mismatch (COUNTERS order vs values order), sweep logic, clear_partials deleting in-flight partials from active fetches, referenced() reading index files, sweep being synchronous blocking on tokio runtime (blocking calls in async context — the admin route calls app.sweeper.sweep(dry_run) synchronously inside async handler, blocking the executor; also spawn_sweeps calls app.sweeper.run().await which does blocking I/O inside async task). Also clear_partials deletes ALL files in incoming regardless of age — in-flight downloads! A sweep during an active fetch deletes the partial being written. That's a real bug: no min_age applied to partials. Also the comment says "A file in incoming is a fetch that is not coming back" but active fetches write to incoming.

Also sweep route placed in untimed router but sweep could take long; fine.

Metrics: values() returns [sweep_bytes_reclaimed, sweep_blobs_removed] but COUNTERS lists blobs_removed first then bytes_reclaimed. COUNTERS is in order: cache_hits, cache_misses, upstream_failures, policy_refusals, sweep_blobs_removed_total, sweep_bytes_reclaimed_total. values() order: cache_hits, cache_misses, upstream_failures, policy_refusals, sweep_bytes_reclaimed, sweep_blobs_removed. So the doc says "Keeping the two side by side is what stops a fifth counter from being rendered under a fourth one's name" — but the mismatch means bytes_reclaimed rendered under blobs_removed name. Bug! Need to check metrics.rs render code to confirm values and COUNTERS are zipped in order.

Also config validation: cache_min_age not validated (could be zero, fine). sweep_interval validated. cache_min_age zero is allowed — fine.

Let me read the actual files in pr/.
I'll read the changed files under `pr/` to verify the logic against real linenumbers.
└ 465 tok ·  84.1 tok/s · 12K ctx · 2224ms ttft ·  5.5s wall
↳ read_file: read pr/services/proxy/src/metrics.rs
└ read_file: read complete
↳ read_file: read pr/services/proxy/src/sweep.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 --
Now check key issues:

1. **Metrics counters mismatch** (confirmed): COUNTERS order at line 51-57 is `sweep_blobs_removed_total` then `sweep_bytes_reclaimed_total`, but `values()` (line 94-95) loads `sweep_bytes_reclaimed` first then `sweep_blobs_removed`. So bytes are rendered under the blobs-removed name and vice versa. That's a real bug. Also docs/operations.md references `cairn_proxy_sweep_bytes_reclaimed_total` — will show blob count. 🔴.

2. **`sweep` route bypasses the one-at-a-time mutex** (line 76: `app.sweeper.sweep(dry_run)` calls `sweep` directly, not `run()`). The module doc promises one sweep at a time via `running: Mutex`. A concurrent sweep request + background sweep would interleave. Actually the doc says the mutex keeps "this module's one-at-a-time promise" — but `sweep()` is pub and called without the lock. 🔴 or 🟠.

3. **Blocking synchronous I/O on the async runtime**: `sweep()` is a sync function doing `fs::read_dir`/`fs::remove_file` over the entire store, called directly from the async handler `sweep()` in admin.rs line 76 and from `spawn_sweeps` in main.rs (`app.sweeper.run().await` → sync `self.sweep(false)` inside async task). The module doc acknowledges the walk is synchronous deliberately, but that means blocking the tokio runtime worker thread. With a 65k-dir store, this could block a worker for seconds/minutes, stalling other requests. In main.rs `spawn_sweeps`, run().await blocks a tokio worker thread. 🟠 performance.

4. **Dry-run + partials**: `clear_partials` with dry_run counts without removing — fine. But note: `clear_partials` in dry-run mode returns 0 if dir missing; fine.

5. **`remove = !index.contains_key(hex)` — a blob referenced by index never gets evicted even when over the ceiling**: if all blobs are referenced and store over ceiling, the loop iterates but `remove` false for all, so it can never bring the store under the ceiling. Wait — condition `remaining >= self.max_bytes && candidate.age >= self.min_age`. If index contains all blobs, nothing is removed and the store stays over ceiling forever. That's arguably intended (docs say "removes blobs no index entry points at and then the oldest blobs") — docs claim the oldest are removed to get under ceiling, but referenced blobs are protected. Actually the doc says "then the oldest blobs until the store is back within CAIRN_CACHE_MAX_BYTES" — but code never removes referenced blobs, so the store can permanently exceed the ceiling if everything is still indexed. That's a mismatch between documented behavior and code; consequence: full disk despite sweep. 🟠/🟡. Hmm, is it a defect? The whole point of the sweep is to enforce the ceiling. If the index never gets pruned except by sweep, blobs stay referenced until removed... `forget` removes index entries only for blobs that were removed. So a store whose blobs are all indexed can never shrink. The min_age grace means new blobs are protected, but old ones too if still indexed. The index is only pruned by purge or sweep's forget. So over time a cache of active deps could exceed the ceiling indefinitely. This is a real behavioral gap: eviction by LRU is impossible while referenced. I'd call it 🟠: ceiling unenforceable; store can grow past max_bytes without bound (bounded by index size only).

6. **`remaining >= self.max_bytes` check uses `held` total computed from candidates including... only blobs; fine. But the `hex` from file_name: for blobs under `blobs/sha256/xx/hash`, file_name is the hash hex — but what if a subdirectory file? fine.

Also candidate path file_name for index entries isn't relevant. But note: `!index.contains_key(hex)` — a blob whose filename is not valid hex but exists would be treated as unreferenced and deleted. Blobs are named by digest so fine.

7. **Race: sweep removes blob then `forget` removes index entries; but a concurrent cache request could serve... between removal of blob and index entry, a request resolving via index would miss and refetch — fine. But more importantly: a fetch in progress writes blob then writes index entry. Sweep reads index first, then walks blobs; a blob just added after index read that isn't in index snapshot gets deleted as unreferenced! Classic TOCTOU: index snapshot taken before blob walk. A blob written between `referenced()` and `collect(BLOBS)` will not appear in index map → deleted even though it's referenced and possibly about to be served/min_age grace. The min_age grace does NOT apply to unreferenced blobs (age doesn't enter into first reason). So a just-downloaded blob could be deleted before its index entry is written, or while a serve is streaming it. Window: sweep collects index, then collects blobs; a cache miss concurrently finishing writes blob, then writes index. If sweep reads blobs after blob write but index snapshot predates index write → blob deleted. Then the index entry points at a missing blob → refetch (stale entry costs a refetch; actually forget won't remove it since not in gone... it stays stale). Not data loss, but violates min_age grace and can thrash. 🟡.

Actually more severe: cache serve path — does serving read the index then stream blob? If sweep deletes a blob mid-stream, download fails. That's inherent to eviction though.

8. **`clear_partials` deletes files in `incoming` that are actively being written by in-flight fetches!** The BlobWriter writes to a temp file in incoming; a sweep deletes all files in incoming, including those belonging to in-flight fetches, not just abandoned ones. The doc says "A file in `incoming` is a fetch that is not coming back" — but an in-flight fetch IS coming back. Deleting the partial under a live writer: the writer will continue writing to the unlinked fd (POSIX) and then rename... rename of a deleted path fails → fetch fails. This breaks concurrent fetches every 15 min. 🟠. Need to check store.rs to see how BlobWriter works. Let me read store.rs.

9. **Dry-run clears nothing but still `removed` count includes partials? `partials` counted fine.

10. **admin.rs sweep handler is sync fn in async context** — `reclaim` is sync, blocking the executor. Also as noted.

11. **config.rs**: `Duration::from_hours` / `Duration::from_mins` — std Duration has no from_hours/from_mins! Wait — is this a custom Duration? config.rs imports std::time::Duration presumably. `Duration::from_hours` doesn't exist in std. Hmm, maybe they have a helper. Let me check config.rs. If it's std, this doesn't compile. Let me read config.rs. Actually maybe they have extension trait. Need to check.

12. **min_age not validated**: sweep_interval validated zero, cache_min_age could be zero — fine (means no grace). Not a bug.

13. **routes/mod.rs**: comment claims sweep "legitimately takes longer than ten seconds" outside timeout — but the sweep route is synchronous blocking; the TimeoutLayer removal is deliberate. But note the middleware `echo_request_id` applied — fine.

14. **main.rs spawn_sweeps**: first tick one interval away — with `interval`, first tick completes immediately! `tokio::time::interval` fires the first tick immediately. The comment says "The first tick is one interval away" — that's wrong; tokio's interval first tick is immediate. So the proxy sweeps immediately at startup. Consequence: contrary to comment; also sweeps right at start (mostly harmless but contradicts doc and metrics). Actually the code comment in main.rs says the first tick is one interval away — that's a factual error; tokio interval's first tick returns immediately. So the first sweep happens at startup. Is that a bug? It means an operator hitting /v1/admin/... no; it means sweep runs at startup, which contradicts the stated intent but functionally mostly benign (dry clearing partials of in-flight fetches though — see #8). I'd report 🟡: first tick immediate, comment wrong, sweep runs at boot.

Let me verify tokio behavior: `interval` — "The first tick completes immediately". Yes.

15. **sweep route: synchronous blocking call in async handler without spawn_blocking** — combine with #3.

16. **`forget` deletes index entries for blobs removed, but in dry_run mode, `gone` includes blobs that would be removed, and `forget` actually removes index files even during dry run!** Look: in `sweep`, `if !dry_run { remove blob }` but `gone.push(hex)` happens regardless, and `forget(&index, &gone)` is called unconditionally — deleting index entries even in a dry run! That's a real bug: dry run is documented as "without removing anything" but it deletes index entries. And the blob remains while the index entry is gone → refetch (cache miss) and re-download, actually worse: blob still on disk but unreferenced → next sweep deletes it. So dry run destroys cache coherence. 🔴. Line 140 + 125.

Yes that's a definite bug.

17. **Also in dry run, the `remove_file` errors for index removal in forget.** Same bug.

Now check store.rs to verify BlobWriter/incoming behavior and IndexEntry, Digest::parse, blob layout (blobs/sha256/xx/hash), and whether remove leaves stale entries.

Also check routes/mod.rs current file for RequestId, timeout.

Also check config.rs for Duration::from_hours.
Now let me check the store module (for the writer/incoming layout and index semantics) and the config (for `Duration::from_hours`).
└ 2187 tok ·  98.2 tok/s · 18K ctx · 2514ms ttft · 22.3s wall
↳ 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
-- reasoning --
Let me check config.rs further — particularly `Duration::from_hours` and `Duration::from_mins` (those are unstable Rust APIs; std Duration has from_secs, from_millis; from_hours/from_mins are unstable). Also check parse_duration. Let me read more of config.rs.
└ 115 tok ·  77.8 tok/s · 23K ctx ·  932ms ttft ·  1.5s wall
↳ read_file: read pr/services/proxy/src/config.rs
└ read_file: read complete
↳ search_files: search pr/services/proxy/src for from_hours|from_mins
└ search_files: search complete
-- reasoning --
Check if `Duration::from_hours` / `from_mins` are std — no, std Duration doesn't have from_hours or from_mins. Wait, Rust std added `Duration::from_hours`? No. std has from_secs, from_millis, from_micros, from_nanos. But `Duration::from_hours` was stabilized in Rust 1.88? Let me recall: Rust 1.88 stabilized `Duration::from_mins`? Actually there was work on `Duration::from_hours`, `from_minutes`... Hmm. I recall `Duration::from_mins` was stabilized in Rust 1.88 (2025). Yes — Rust 1.88.0 (June 2025) stabilized `Duration::from_mins`, `from_hours`? Let me think. The PR "Stabilize `Duration::from_mins`" — there's a tracking issue for `duration_from_mins`? Actually there's `Duration::from_hours` and `from_mins` unstable features... I believe `duration_from_mins` was stabilized? Hmm, not sure. Actually I recall Rust 1.88 stabilized... Let me not guess; check the test file at line 350 uses from_mins too — pre-existing tests. Test line 350 was presumably already there (parse_duration test). Check git: the diff doesn't touch tests. If tests already used from_mins, it compiles in the baseline. So from_mins/from_hours must exist in their toolchain. Let me check whether test at 350 is pre-existing — check pr/services/proxy/src/config.rs around 340-360, and also check the test for parse_duration in the baseline? We only have pr/ tree. Line 350's test presumably pre-existing since the diff didn't touch it. So those functions exist — not a defect.

Now the real logic review. Key areas:

1. **collect() in `referenced()` for INDEX**: `collect` pushes Candidates with size and age — that's fine, we only use paths. But note: `collect` for index files... fine.

2. **sweep removes blobs not in index, regardless of age** — including blobs whose index entry was just written but... hmm. Race: a blob is committed and then `link` writes the index entry. Between commit and link, a sweep could remove the blob because the index doesn't reference it yet. The cache route: fetch → writer commit → store.link. If a sweep runs between, the blob is deleted, index entry stale → next request misses and refetches. That's a single refetch — not fatal, but could happen repeatedly under load? It's the design trade-off already acknowledged in doc comments ("keeping one for an hour only holds bytes nothing is going to ask for"). Hmm, actually worse: index entry points at blob deleted; resolve returns Some, open_blob returns None → miss → refetch. Fine-ish.

Actually wait, worse: the delete-then-refetch happens on a *hot* path — a blob just fetched (age < min_age) but not yet linked gets removed, and the link will then re-... The link still writes index. OK marginal.

3. **The `remaining >= self.max_bytes` loop and `bytes += candidate.size` counting**: A blob that's already gone (remove_file fails) still counts bytes and removed. Known/acknowledged in comment. Not a defect per se.

4. **`remaining` counts only blobs, but the ceiling says "the most the blob store may hold"** — incoming partials are deleted first, ok.

5. **Big issue: removal loop stops when?** It removes candidates while remaining >= max_bytes, but for unreferenced blobs it removes ALL of them regardless. Fine. For referenced over-ceiling: removes oldest with age >= min_age. But: the loop iterates candidates sorted oldest first; once remaining < max_bytes, later (newer) referenced candidates are skipped — good. But unreferenced ones are removed regardless. OK.

But subtle bug: after removing a candidate whose remove_file failed, remaining still decreases and bytes counts it — overcounting metrics. Minor/acknowledged.

6. **Concurrency between background sweep and on-demand route**: `run()` takes the mutex, but `sweep()` (called by admin route via `app.sweeper.sweep(dry_run)`) does NOT take the mutex! Look: `run()` locks `running`, then calls `self.sweep(false)`. The route calls `app.sweeper.sweep(dry_run)` directly — bypassing the mutex. The module doc says "One sweep at a time" and the type comment claims the Mutex keeps the promise. But the route path calls sweep() directly without locking. So a POST /v1/admin/cache/sweep concurrent with a background interval sweep → two sweeps at once → double eviction, "take the store far below the ceiling". That's a real bug. Also two concurrent POSTs to the sweep route.

Line refs: pr/services/proxy/src/routes/admin.rs:76 (`app.sweeper.sweep(dry_run)`) vs sweep.rs:82-85 (run locks; sweep doesn't). This is the top finding — severity orange/red? Consequence: over-eviction, cache thrashing, potentially incorrect accounting. It's a correctness bug in the one-at-a-time promise. I'd say 🟠.

Also the dry-run route: a dry run while background sweep running — same race, double-counting deletion? Dry run doesn't delete. But two non-dry runs overlap.

7. **`clear_partials` deletes ALL files in `incoming`, including active in-progress fetches!** `BlobWriter` writes temp files into `incoming/` while a download is in progress. A sweep deletes every file in `incoming` — including temporaries belonging to live downloads. Then when the writer commits, `fs::rename(&temp, &target)` fails (file deleted) → fetch fails, or worse: on Linux, the rename fails with ENOENT → error. Actually the file handle... rename uses the path; if the file was unlinked, rename fails ENOENT → the whole fetch errors out. So a periodic sweep every 15m kills any in-flight downloads longer than the sweep timing. Doc comment says "A file in `incoming` is a fetch that is not coming back" — but active fetches DO have files in incoming. The write path: writer() creates temp in incoming, streams bytes (could be minutes for 200MB), commit renames. Sweep deletes it mid-flight → commit fails → cache miss error returned to client. This is a real bug: 🟠/🔴. The comment claims partials carry no digest and nothing can look them up — true, but live writers hold the handle. On Unix, deleting an open file doesn't break the writer's writes (writes go to the unlinked inode), but `commit`'s rename by path will fail with ENOENT. So the fetch fails after downloading all bytes. Severity: orange (high). Line: sweep.rs:224-240 (clear_partials) — no age check; contrast with the blob path which respects min_age. Also `held` doesn't count incoming bytes, and the sweep runs even when under ceiling — clear_partials is unconditional (line 91), so every 15 min it kills any download in progress. Definitely report. Maybe 🔴 given a slow 200 MiB fetch over a slow link easily exceeds a window? Well, the sweep is periodic (every 15 min); probability a given fetch overlaps is real under load. I'd rate 🟠 or 🔴. Consequence: legit concurrent downloads fail. I'd say 🟠 high.

Hmm, is there any protection? BlobWriter holds an open File handle; deletion is possible on Unix. commit does `fs::rename(&temp, &target).await?` → ENOENT → error propagates. Yes, failure.

8. **`forget()` and `gone` includes unreferenced digests**: forget removes index entries for digests that were removed. For blobs removed because unreferenced, index.get(hex) is None → no-op. Fine.

But subtle: `forget` deletes index entries for removed blobs — but a concurrent `link()` could have written a new index entry pointing at that digest between the sweep's collect and forget... race acknowledged? The purge route has the same class. Eh.

9. **Race: sweep vs. concurrent store writes on the serve path.** Blob commit + link: sweep reads index (line 92) after clear_partials; a blob committed and index written after `referenced()` returns won't appear in index → treated as unreferenced → deleted while a client is being served from it! Worse: it's deleted, then forget() removes the fresh index entry. The serve path: resolve → open_blob streams file. If sweep unlinks while streaming, on Unix the open fd still serves fine. But the index entry removed → next request refetches. Same trade as min_age... but here even fresh blobs (age < min_age) are removed because "age does not enter into the first". This is a deliberate documented decision. The refetch cost is acknowledged. I won't report as a defect since it's explicitly designed (comment at 114-118). Though arguably the window commit→link is the real hazard: blob is written and link() not yet called, sweep deletes blob, then link writes entry pointing to nonexistent blob — one refetch, fine.

10. **Metrics COUNTERS vs values ordering**: COUNTERS order is hits, misses, upstream_failures, policy_refusals, sweep_blobs_removed, sweep_bytes_removed. values() returns ... sweep_bytes_reclaimed, sweep_blobs_removed. Mismatch! COUNTERS[4] = "cairn_proxy_sweep_blobs_removed_total" pairs with values[4] = sweep_bytes_reclaimed. So the blobs-removed name gets bytes value and bytes-removed name gets blobs value. doc says "Keeping the two side by side is what stops a fifth counter from being rendered under a fourth one's name" — exactly the bug introduced. records doc/operations.md references `cairn_proxy_sweep_bytes_reclaimed_total` — its value would actually be blobs count. Real bug: 🔴? Severity: metric renders wrong values under names — operator alert on wrong data. I'd say 🟠 (high) — it silently swaps two counters. Line: metrics.rs:88-96 values() vs COUNTERS at 51-57. One line: metrics.rs:94 (or the values array). Report at metrics.rs:94.

11. **`app.metrics.record_sweep` in main's spawn_sweeps and admin both** — fine.

12. **Dry-run clears partials?** clear_partials with dry_run=true doesn't remove but counts. Good.

13. **`held` for dry run** — fine.

14. **The on-demand route bypasses the mutex (finding 6) — also the route's sweep runs synchronously on the tokio runtime thread!** `reclaim` calls `app.sweeper.sweep(dry_run)` which is blocking (std fs walk of 65k dirs) inside an async handler — blocks a tokio worker thread for potentially a long time. The module doc even acknowledges the walk is synchronous, and they deliberately put the route outside the TimeoutLayer ("a sweep of a large store legitimately takes longer than ten seconds"). But blocking the async executor is bad: the doc says the walk is sync and justifies it, but the background sweep calls it from `spawn_sweeps` async task too — blocking a runtime worker. This is a real defect: blocking I/O in async context without spawn_blocking. Severity: 🟡/🟠. Line: sweep.rs:84 (`self.sweep(false)` in async fn run) and admin.rs:76. Given doc acknowledges the choice ("The walk is synchronous... One pass of standard-library calls costs less than the scheduling would") — they considered tokio::fs but not spawn_blocking. Still blocks the multithreaded runtime's worker. With a multi-thread runtime and many workers it degrades but isn't fatal. 🟡.

15. **config validation**: cache_min_age zero allowed — that means sweep can remove any blob immediately? Not validated but arguably intended (min_age 0 = no grace). Not a defect.

16. **`remaining >= self.max_bytes`** uses `>=` so when store exactly at ceiling, removes. Fine.

17. **`scanned` includes index files? No — collect for blobs only. Fine.

18. **`collect` follows symlinks**: `fs::metadata` follows symlinks; a symlinked directory would be recursed into (meta.is_dir() true for symlink to dir) → potential infinite loop with cyclic symlinks, or escaping the store. The comment says links counted at link size — but `fs::metadata` follows the link, so `meta.len()` is the target's size, not the link's size (that would be `symlink_metadata`). So the comment's claim is wrong AND a symlink to a big file outside the store gets counted at its full size and deleted (removing the link, fine) — but more importantly a symlinked directory is recursed into, potentially outside the blob dir → sweep could delete files outside the store! E.g., if index contains symlinks... realistic? "A store moved between volumes often has blobs linked into it" — if hard links, fine (fs::metadata len = file size, correct for hard links). The comment conflates hard links and symlinks. For symlinks: fs::metadata follows, so size is target size, and directories are recursed. Deleting a symlink target? No — remove_file removes the link itself. So risk is: recursing into symlinked dirs and deleting files outside the store root, and overcounting sizes. It's a plausible defect: line 164 (`fs::metadata` should be `symlink_metadata`) and 167-169. Severity 🟡/🔵. Given store is operator-controlled, 🟡? The comment explicitly claims a link is counted at link size — the code doesn't do that. I'd report 🟡 at line 164.

Also `clear_partials` — subdirectories in incoming ignored (remove_file fails on dirs, logs debug). Fine.

19. **forget() removes index entries for blobs that failed to be removed** (remove_file error, e.g. permission): gone still includes hex, forget deletes the index entry → cache entry lost even though blob remains. Minor. Also, when remove fails because another proxy removed it — fine. Edge: remove_file fails with PermissionDenied, blob still on disk but index entry removed → refetch overwrites, fine. Not reporting.

20. **`held`/`scanned` in dry_run for route**: fine.

21. **`SweepQuery.dry_run` bool parse**: `?dry_run=true` works; `?dry_run=1` also. Query rejection errors → axum returns 400 default, not through error.into_response_with — fine.

22. **routes/mod.rs**: sweep route in untimed router — fine, deliberate.

23. **main.rs spawn_sweeps**: `ticks.tick().await` — first tick immediate! tokio's interval: `tick` completes immediately on first call. The doc comment says "The first tick is one interval away" — wrong! tokio::time::interval's first tick fires immediately. So the sweep runs at startup, before the cache has filled — contradicting the doc. Actually is that harmful? First sweep at startup: store under ceiling, but clear_partials still runs and can delete... at startup, no active fetches yet (serve hasn't started? spawn_sweeps is called before axum::serve — the listener is bound but not serving; actually axum::serve is called after, so at first tick (immediate) there are no in-flight requests). Hmm, but the spawned task may run after serving starts? The first tick completes immediately when polled; the task is spawned before axum::serve, so likely runs first. Minor anyway. But the doc-vs-behavior mismatch: doc says first tick one interval away; tokio interval fires first tick immediately. So the comment is wrong and the startup sweep happens — mostly harmless but contradicts stated intent, and on restart of a proxy against an existing over-ceiling shared store, it'd immediately evict. Wait, also in the loop: first tick immediate, subsequent ticks every interval. That matches interval behavior. The defect: doc claim false; behavior: sweep at startup. Is it a "defect I can point at"? main.rs line ~113 `ticks.tick().await` with comment above. I'd report 🟡/🔵 (comment/behavior mismatch; consequence minor). Actually there's a subtle real consequence: on a cold start with an existing full store from a previous run (or shared with another proxy), the immediate sweep deletes blobs that are fresh (age<min_age? no—only if over ceiling and age>=min_age, so fresh ones safe; unreferenced ones deleted regardless). Hmm, low. 🔵.

Actually wait — is the tokio first-tick-immediate true? Yes: "An interval will tick indefinitely. At any point in time... The first tick completes immediately." Confirmed from tokio docs.

24. **MissedTickBehavior::Delay** set before first tick — fine.

25. **`.env.example` CAIRN_CACHE_MIN_AGE comment** — fine.

26. **routes/mod.rs removed the comment** — the timeout comment merged; fine.

27. **admin.rs sweep: `authorise` then synchronous blocking sweep in handler** — covered in 14.

28. **Double-counting on-demand + background**: on-demand route records metrics; background also records. Fine.

29. **`Reclaimed.held` — "Bytes of blob the store held when the sweep started"** — computed after clear_partials; fine.

30. **In sweep: `index.contains_key(hex)`** — hex from filename; blob files named by full hex. Good. But `collect` over BLOBS pushes files at depth blobs/sha256/xx/yy/hex — file_name is hex. Fine.

31. **In `referenced`, `collect` is used for INDEX dir which may contain subdirs — handled. Fine.

32. **`forget` deletes entries for `gone` digests including dry_run**! In dry_run, `gone` is populated (removed incremented, gone.push) but files not removed. Then `forget(&index, &gone)` is called unconditionally — in dry run, it DELETES the index entries for blobs it merely simulated removing! Look: line 140 `forget(&index, &gone);` — no dry_run check. In a dry run, blobs stay but their index entries are removed → the cache effectively breaks: entries point at existing blobs, but entries deleted → next request misses and refetches and overwrites... Actually the blob still exists; refetch will re-link. So the "dry run reports what a sweep would reclaim without removing anything" is false — it removes index entries. And it double-reports? removed counts are simulated, fine, but the filesystem IS mutated. Real bug: 🔴/🟠. Line: sweep.rs:140. Consequence: dry run deletes live index entries, causing refetches; contradicts the documented guarantee. Also subsequent real sweep would then treat those blobs as unreferenced and delete them — so a dry run followed by the regular interval sweep permanently deletes blobs the operator was only asking about. Severity 🟠 or 🔴. I'd say 🟠 (high) — data loss is only cache data (recoverable), but it breaks a documented safety guarantee. I'll go 🟠. Hmm, actually consequence: index entries removed → the blobs become unreferenced → next background sweep removes them (age considered? unreferenced → removed regardless of age). So a dry run causes eviction of everything it reported. Still only cache loss. 🟠.

33. **Blocking call in async also applies to main spawn_sweeps** — same as 14.

34. Metrics doc comment mismatch minor.

Now severity assignments:

- 🔴? The metrics swap: operator alerts on `sweep_bytes_reclaimed_total` which actually shows blob count — misleading monitoring. Also documented alert in operations.md. I'd rate 🟠.
- Dry-run forgetting index entries: 🟠.
- Mutex bypass: 🟠 (or 🟡). Two concurrent sweeps → over-eviction; the module's core invariant. Also means the "one-at-a-time" promise is only kept on one path. 🟠.
- clear_partials kills in-flight downloads: 🟠/🔴. A 200 MiB download at modest speed takes minutes; sweeps every 15m; any fetch in flight during a sweep fails after full download. Under continuous traffic, every sweep breaks concurrent fetches. I'd say 🔴? It's the most impactful user-visible failure. The comment even asserts wrongly that files in incoming are abandoned. I'll rate 🔴... Let me be measured: it fails in-flight requests (client sees error), cache self-heals. High severity 🟠. Hmm. Reviewers may differ. I'll give 🟠 for partials and note commit failure. Actually consequence: every fetch in progress during any sweep (every 15m by default) errors out. That's a recurring outage of the fetch path. I'd call it 🔴 critical? The severity: it breaks core functionality regularly. I'll go 🟠 high... Let me think about what "critical" means: data loss, security, outage. This is effectively periodic fetch failures — service's primary job broken during sweeps. I'll mark 🔴.

Hmm, but wait — is clear_partials really deleting files of live writers? BlobWriter creates temp in incoming via `File::create`. Sweep's `fs::remove_file(entry.path())` unlinks it. The writer continues writing to unlinked inode. On commit, `fs::rename(&temp, &target)` → ENOENT error → fetch fails. Yes. Also even before commit: nothing breaks visibly. So failure at commit time after all bytes downloaded. Confirmed bug.

Also should clear_partials respect age (min_age)? Yes, that would be the fix — skip recent files. The route doc says sweep clears "partial writes left by fetches that died" but the code can't distinguish. Report 🔴 at sweep.rs:230-236. I'll use line 232 (remove_file).

- Symlink metadata: 🟡 or 🔵. `fs::metadata` follows symlinks; comment claims otherwise. If an operator symlinks to save space... eh, speculative but the comment-code contradiction is concrete. 🔵/🟡. Also recursion into symlinked dirs could delete outside the store — that's a real hazard. 🟡.
- Blocking sync fs walk in async handler/task: 🟡.
- First tick immediate vs comment: 🔵.

Also check: `sweep_interval` validated nonzero, but `cache_min_age` not validated — no requirement. Fine.

Also `.env.example` says sweep interval 15m etc. fine.

One more: in `main.rs`, `spawn_sweeps(app.clone())` before `axum::serve` — app built... fine.

Also `run()` holds mutex across blocking sweep — blocks the async thread anyway.

Another: In `sweep()`, `remaining` decrement even when remove fails (acknowledged). Also `bytes` counts files that failed removal → metrics overcount. Minor, comment acknowledges. Skip.

Also `forget` removes index entries even when the blob removal failed → combined effect: purge races. Skip.

Also `collect` in `referenced` uses `fs::metadata` following symlinks again — same.

Also `clear_partials` counts subdirectory remove failures — fine.

Also: the on-demand route holds... `reclaim` is sync fn called in async handler — covered.

One more potential: metrics `record_sweep(reclaimed.removed, reclaimed.bytes)` — args order blobs, bytes — main.rs passes (removed, bytes) ✓; admin passes (removed, bytes) ✓.

Check `RequestId` extractor usage in sweep — same as purge, fine.

Line numbers for findings (in pr/ files, same as diff new-file lines):

1. metrics.rs:94-95 — values() returns bytes before blobs while COUNTERS lists blobs before bytes (lines 51-57). Swap. 🟠.
2. sweep.rs:140 — forget called in dry_run. 🟠.
3. routes/admin.rs:76 — calls sweep() directly, bypassing the `running` mutex (sweep.rs:83 locks only in run()). 🟠.
4. sweep.rs:232 — clear_partials deletes temp files of in-flight downloads; commit then fails with ENOENT. 🔴.
5. sweep.rs:164 — fs::metadata follows symlinks, contradicting the comment; recurses into symlinked dirs → sizes overcounted and deletion can reach outside the store. 🟡.
6. sweep.rs:84 (or admin.rs:76) — blocking std-fs walk inside async context. 🟡.
7. main.rs — first tick immediate. Find exact line number in main.rs. Diff shows `ticks.tick().await;` — need line number. Let me check main.rs.

Also possibly: `held` excludes incoming bytes but ceiling claim; skip.

Also: In dry run, `clear_partials` counts but doesn't remove — correct. And Reclaimed.partials reported — fine.

Let me get main.rs line numbers.
One more file to pin line numbers in `main.rs` and confirm the router state:
└ 5465 tok · 118.3 tok/s · 25K ctx ·  961ms ttft · 46.2s wall
↳ read_file: read pr/services/proxy/src/main.rs
└ read_file: read complete
-- reasoning --
Now let me think about the defects.

1. **`clear_partials` deletes files a live fetch is writing.** `sweep.rs:224-239`: the sweep removes every file in `incoming/` regardless of age. But `BlobWriter` writes temp files to `incoming/` during live fetches (store.rs:171-180, `temp_path` puts them in `incoming_dir()`). An active fetch (a 200 MiB download taking minutes) has its temp file deleted mid-write; the writer keeps writing to the unlinked inode, and at commit the rename fails (file gone) — the fetch fails after downloading everything. Actually commit's rename returns error → fetch fails. That's a real bug: concurrent in-flight fetches are killed by every sweep. Worse: it also removes the in-flight temp file, and `BlobWriter::drop` will try to remove it again (NotFound error, warn logged). The consequence: every 15-minute sweep kills any download in flight. The doc even claims the min_age grace protects in-flight fetches of a package a pipeline job fetched — but only blobs, not partials. Defect at sweep.rs:91 / clear_partials 230-237. Severity: orange (high).

2. **Ceiling enforcement with unparseable/never-indexed blobs**: `remaining >= self.max_bytes` — blobs with no index entry are removed regardless. Fine.

3. **`forget(&index, &gone)` removes index entries for blobs removed because over ceiling** — that's intended.

But wait: `forget` is called even in dry_run mode? In dry run, `gone` is populated (remove candidates computed) but files not removed. `forget` unconditionally removes index entries for "gone" blobs — in a dry run, it deletes the index entries while leaving blobs! Line 140: `forget(&index, &gone)` runs regardless of `dry_run`. So a dry run mutates state: it deletes index entries naming digests the sweep claims it would remove, while not removing the blobs. Consequence: dry run is not side-effect-free; next request for those coordinates misses (refetch). That's a real bug — the route documents dry run as "reports what a sweep would reclaim without removing anything". Defect at sweep.rs:140 (and admin.rs route doc). Orange/red? Data loss is not permanent (refetch), but it's a "dry run writes" bug. I'd say orange.

4. **`referenced()` uses `collect()` which uses `fs::metadata` (follows symlinks) — fine.

5. **Index walk counts only files; index dirs recursion fine.**

6. **Concurrency: `sweep()` is called from async route but does synchronous blocking fs work on the runtime thread** — the module doc justifies this for the background task ("one pass of standard-library calls costs less than the scheduling would"), but the admin route now calls `app.sweeper.sweep(dry_run)` synchronously in an async handler (admin.rs:76), blocking a tokio worker thread for potentially minutes on a large store, and the route is deliberately placed outside the timeout so a 10s TimeoutLayer won't cover it. This starves the multi-thread runtime worker for the whole walk (readdir of 65k dirs, thousands of unlinks). Should be `spawn_blocking`. Severity: orange/yellow. The module doc rationalises it for the background sweeper but the route reuses it. I'd call it orange (availability) or yellow. Hmm. The doc at sweep.rs:14-18 explicitly says sync walk is intentional. But the route blocks a runtime worker. With rt-multi-thread default worker count = cores, one blocked worker on a big store — degradation. Also the route holds... it doesn't hold the mutex — wait! **The admin route calls `sweeper.sweep()` directly, not `run()`**, so it bypasses the `running` mutex entirely. The module doc says "One sweep at a time... the type keeps rather than something every caller remembers" (sweep.rs:65-67), but the route caller remembers nothing: `admin.rs:76` calls `sweep()` which takes no lock. So a manual sweep can run concurrently with a background sweep — exactly the interleaving the mutex exists to prevent, with each computing totals from a store the other is changing, over-evicting and double-counting bytes in metrics. That's a genuine high bug: admin.rs:76 should call `app.sweeper.run().await` (and there's no dry-run variant under the lock). Defect: two problems at same site — bypasses the mutex AND blocks the executor. I'll report as two findings or one combined. Format policy: one line per defect. I'll do:
   - 🔴/🟠 admin.rs:76: manual sweep calls `sweep()` directly, bypassing the `running` mutex that `run()` holds → concurrent with background sweep, both compute from totals the other changes.
   - 🟠 admin.rs:76 (or sweep.rs:90): synchronous blocking FS walk executed on the async runtime worker in a handler.

7. **Metrics order/name mismatch?** COUNTERS order: blobs_removed then bytes_reclaimed. `values()` returns bytes then blobs (lines 94-95). zip pairs COUNTERS[i] with values[i]: COUNTERS[4] = sweep_blobs_removed_total paired with values[4] = sweep_bytes_reclaimed. **Swapped!** The blob-removed counter renders bytes_reclaimed's value and vice versa. That's a clear bug — exactly what the comment at metrics.rs:30-32 says the side-by-side keeping is meant to prevent. Defect: metrics.rs:94-95 vs COUNTERS 50-57. Severity: red? It corrupts both sweep metrics — an operator alerting on `sweep_bytes_reclaimed_total` (operations.md explicitly says to watch it) gets the blob count. Critical for the documented alert. I'd say 🔴 bug. Or orange. Operations doc says "Watch `cairn_proxy_sweep_bytes_reclaimed_total`: a sweep reclaiming nothing on a volume that is filling means everything is referenced" — with the swap, a sweep removing 0 blobs shows bytes=0 which is correct by coincidence when nothing removed (both 0). But when something removed, bytes shows count of blobs (tiny) → operator thinks little reclaimed → misdiagnosis. Still a real metrics corruption. 🔴.

8. **`age_of` flatten: future mtime → age 0 → never removed by ceiling (age < min_age) — but if unreferenced it's removed anyway. Fine, documented.

9. **`collect` on `blobs/sha256`: `fs::metadata` follows symlinks; for symlinks, is_dir false, meta.len() is target's size... doc comment says links counted at link size — but `fs::metadata` follows symlinks, giving target size, contradicting the comment. Minor doc/impl mismatch. `fs::symlink_metadata` would give link size. Low (blue) — comment claims behavior the code doesn't implement. Actually the comment says "A link is counted at the size of the link" — with `fs::metadata`, a symlink to a large file counts as the target's size. Consequence minimal. 🔵.

10. **`held` includes... fine.

11. **Sweep removes blobs not in index even if they're currently being served / just written but not yet linked.** Race: fetch commits blob (rename into blobs/), then `link()` writes the index entry (store.rs:135-153). Between commit and link, a sweep sees a blob no index entry points at → deletes it → link succeeds → index points at nonexistent blob → every serve misses and refetches, then re-links... actually on miss it refetches and re-links, so self-healing but the just-fetched package is immediately evicted — the min_age grace is defeated for the window. Also with concurrent fetches this makes the "package one job in a pipeline fetched is still there for the next" claim false in a race window. Medium. Race window is small (commit→link), but the sweep takes the referenced snapshot at start; a blob committed after `referenced()` ran but before the unlink loop gets deleted even though its link is written by then. Actually ordering: sweep does clear_partials, then referenced(), then collect blobs, then unlinks. A fetch that commits+links during the walk: if link happens before referenced() snapshot, safe. If commit happens after referenced() ran → blob is a candidate with no index entry → removed. So any fetch completing during a sweep's (long, minutes on big store) walk has its blob deleted. That's a genuine high bug under load — same class as #1. Combined consequence: concurrent fetch traffic gets its results evicted. Report as 🟠 sweep.rs:119 (`!index.contains_key(hex)`) — blobs committed between the index snapshot and the unlink pass are deleted even though they were just linked.

Also `forget` deletes the index entry for the just-linked blob → subsequent resolve is a miss... consistent with eviction; the refetch re-creates. Still eviction of fresh blobs.

12. **`remaining >= self.max_bytes` — off-by... not a defect.

13. **Config: `cache_min_age.is_zero()` not validated — CAIRN_CACHE_MIN_AGE=0 accepted. Minor, deliberate? Setting min age 0 means immediate eviction; not clearly a defect.

14. **Duration::from_hours / from_mins** — these are stable? `Duration::from_hours` and `Duration::from_mins` were stabilized in Rust 1.84? Actually `Duration::from_mins`... Let me recall: `Duration::from_weeks`, `from_days`, `from_hours`, `from_mins`, `from_secs` — `from_secs_f` etc. `Duration::from_mins` was unstable for a while (`duration_from_min`? no). `Duration::from_minutes`? The stable API: `Duration::from_secs`, `from_millis`, `from_micros`, `from_nanos`, and `from_hours`/`from_days`/`from_weeks`... Hmm. `Duration::from_hours` — I believe `from_hours`, `from_days`, `from_weeks`... Actually I recall these being unstable features `duration_constructors` stabilized in Rust 1.81 or so? Let me think. `Duration::from_hours` etc. were unstable (`duration_constructors`) for a long time; I believe they were stabilized in Rust 1.84 (Jan 2025)? There's `duration_constructors_lite`? I recall `Duration::from_mins`... I'm not certain. The existing test at line 350 uses `Duration::from_mins(2)`, so presumably it compiles in this codebase (existing code already used it? line 350 is in the diff? No — the test lines 350-351 aren't in the diff, so `parse_duration` already used `from_mins`/`from_hours` before. So it compiles. Not a defect.

15. **`spawn_sweeps` doc: MissedTickBehavior::Delay — comment says "The next one starts a full interval after this one finished" — that's actually what Delay does relative to tick completion. Fine.

16. **Router: sweep route in untimed group — intended.

17. **`held` vs sweep semantics: `remaining >= self.max_bytes` removes until below ceiling. Fine.

18. **`clear_partials` also runs during dry_run? No — in dry run it doesn't remove but counts. Good. But it counts entries it can't remove? If remove fails it continues without counting. Fine.

19. **`forget` in dry run — covered in #3.

20. **`reclaim()` in admin route is sync fn doing blocking work while holding... no lock. Covered.

21. **Metrics record_sweep ordering in main.rs: fine.

22. **`.env.example` CAIRN_CACHE_MIN_AGE — fine.

23. **routes/mod.rs doc: "Six routes" — count: healthz, readyz, metrics, purge, cache, sweep = 6. Fine.

24. **admin.rs sweep: `Query<SweepQuery>` with `dry_run: bool` — accepts `?dry_run=true`/`1`... serde bool from query: accepts "true"/"false". Fine.

25. **Dry-run record metric: fine.

26. **`sweep` route placed in untimed — meaning an unauthenticated? No, authorise inside.

Severity assignment:
- Metrics swap: 🔴 (documented alert fires wrongly / both sweep metrics corrupted).
- clear_partials deletes live in-flight temp files: 🟠.
- Dry run deletes index entries (mutates state): 🟠.
- Manual sweep bypasses mutex (concurrent sweeps): 🟠.
- Race evicting just-committed blobs between index snapshot and unlink: 🟡 (self-healing but defeats min_age; consequence one refetch per affected package, plus stale index entries deleted).
- Blocking async runtime worker: 🟡 or fold into mutex finding. I'll report separately as performance 🟡 at admin.rs:76? Two findings at same line is fine.
- Symlink metadata comment mismatch: 🔵.

Wait, on #5 (race): is it worth including? It's concrete and pointable at sweep.rs:119. Keep 🟡.

Also check: `referenced` collects index files including... `collect` recurses into dirs; index temp files? `link` writes temp then renames; temp in `incoming_dir`? `temp_path` uses incoming dir — yes, store.rs:147-152: temp path is in `incoming`, then renamed to index path. So index temps live in incoming and get swept by clear_partials — fine, and a live index temp write would be deleted by clear_partials too (same bug class as #1, narrower window).

Also `forget` removes index entry files, but only those in the `index` snapshot — fine.

One more: in `sweep`, `held` counts blobs at start; ceiling logic uses `remaining` — blobs that failed to unlink still counted as removed/bytes (line 134-137 increments even if remove_file errored). So metrics/report overcount reclaimed bytes when unlink fails (e.g., another proxy already removed, or permission). Comment says "usually already gone" but then bytes/removed still counted. If the file was already gone, counting its bytes as reclaimed is wrong — store didn't shrink by those bytes, so remaining underestimates the true store size... wait, remaining is decremented, so sweep stops removing earlier than it should, leaving store above ceiling. Consequence: after a purge race, sweep believes it reclaimed bytes it didn't, and the ceiling check uses the wrong remaining → store may stay over the ceiling for another interval. 🟡. That's at sweep.rs:125-137: failed unlink still counts blob as removed and bytes reclaimed. Good catch.

Also duplicate hex names? Each blob filename unique per digest by layout, so hex unique. Fine.

Line numbers for findings:
- metrics.rs:94-95 — swapped pairing. Point at 94 (bytes loaded in blobs_removed's slot). Actually COUNTERS index 4 = blobs_removed (line 51), values[4] = bytes (line 94). So metric named blobs_removed_total renders bytes value. Point at metrics.rs:94.
- sweep.rs:91 / clear_partials at 232: deleting live temp files. Point at sweep.rs:232.
- sweep.rs:140 forget in dry run. Point at sweep.rs:140.
- admin.rs:76 bypasses lock.
- admin.rs:76 blocking — maybe combine: "runs the blocking sweep inline on the runtime thread and without the mutex; both belong in run()". Policy says one defect per line; I could do two lines same address or one line covering both. I'll make it one finding about mutex bypass (correctness) and one about blocking (performance) — different categories.
- sweep.rs:134-137 failed-unlink accounting: point at sweep.rs:137.
- sweep.rs:119 race.
- sweep.rs:164 symlink comment.

That's 8 findings, all concrete. Maybe drop the weakest? The symlink one is a doc/impl mismatch, low but pointable. Keep as 🔵.

Double-check #1 severity: sweep interval 15m, downloads can take minutes (200 MiB, timeouts). Every sweep kills in-flight fetches → those fetches fail (commit rename of unlinked file: rename works on open fd? On POSIX, rename of an unlinked-but-open file fails ENOENT since the path is gone). So fetch errors → client sees failure. Also bytes downloaded are wasted. Under continuous traffic, every 15 min some downloads die. 🟠 high — could argue red. I'll keep orange.

Check the metrics swap again carefully. COUNTERS:
[0] cache_hits, [1] cache_misses, [2] upstream_failures, [3] policy_refusals, [4] sweep_blobs_removed_total, [5] sweep_bytes_reclaimed_total.
values(): [hits, misses, failures, refusals, bytes, blobs].
zip: (sweep_blobs_removed_total, bytes), (sweep_bytes_reclaimed_total, blobs). Yes, swapped. 🔴 since operations doc tells operators to alert on bytes_reclaimed.

Also check `Metrics::values` doc comment line 30-32 "in the order values reads them" — contradicted. Fine.

Write findings.
Review complete. Findings, all tied to lines in the changed files:

🔴 `bug` services/proxy/src/metrics.rs:94: `values()` returns `sweep_bytes_reclaimed` and `sweep_blobs_removed` in the opposite order to `COUNTERS` (metrics.rs:51-57), so `render()`'s zip publishes the blob count under `cairn_proxy_sweep_bytes_reclaimed_total` and the byte count under `cairn_proxy_sweep_blobs_removed_total`. operations.md tells operators to alert on the bytes counter specifically, so the alert reads blob counts (e.g. 12 blobs) as bytes reclaimed.

🟠 `bug` services/proxy/src/sweep.rs:232: `clear_partials` unlinks every file in `incoming/` with no age check, but that is where `BlobWriter` (store.rs:201-206) keeps the temp file of a fetch currently in progress. A 200 MiB download spanning a sweep loses its file mid-write; `commit`'s rename then fails on a path that no longer exists and the whole fetch errors after all bytes were transferred. Every sweep interval kills every in-flight download.

🟠 `bug` services/proxy/src/sweep.rs:140: `forget(&index, &gone)` runs unconditionally, including for a dry run, so `?dry_run=true` — documented in admin.rs:58-60 as reporting what a sweep "would reclaim without removing anything" — still deletes the index entries for every digest it would have removed. The dry run is a write, and each dry run forces a refetch (and re-link) of every blob it merely reported on.

🟠 `bug` services/proxy/src/routes/admin.rs:76: the on-demand route calls `sweeper.sweep(dry_run)` directly instead of `sweeper.run().await`, bypassing the `running` mutex (sweep.rs:82-85) that exists precisely so two sweeps never interleave. A manual sweep concurrent with the background one makes both compute removals from a total the other is already shrinking, over-evicting past the ceiling and double-counting bytes in the metrics.

🟠 `bug` services/proxy/src/routes/admin.rs:76: the synchronous directory walk and unlinks (sweep.rs:90-149) run inline on a tokio worker thread; on a store with tens of thousands of blobs the module's own estimate (sweep.rs:14-17) this blocks a runtime worker for minutes while serving requests, and the route is deliberately exempted from the `TimeoutLayer` (routes/mod.rs:122-130) so nothing bounds it. It belongs in `run()` under `spawn_blocking` (or the lock held across a blocking task).

🟡 `bug` services/proxy/src/sweep.rs:119: a blob committed by an in-flight fetch between the `referenced()` snapshot (sweep.rs:92) and the unlink loop is absent from the index map and is deleted as unreachable, even though its index entry is written moments later — so `forget` (sweep.rs:140) then deletes that fresh entry too. On a long sweep of a busy store this evicts just-fetched packages, defeating the `CAIRN_CACHE_MIN_AGE` grace the docs promise.

🟡 `bug` services/proxy/src/sweep.rs:134: when `fs::remove_file` fails (sweep.rs:126-131), the candidate is still counted: `remaining` is reduced, `bytes` and `removed` incremented, and its digest pushed to `gone`. A blob that was already gone via a purge gets reported as reclaimed bytes the store never gave up, and `remaining` then under-counts the true store size, letting a sweep stop while the store is still over its ceiling.

🟡 `bug` services/proxy/src/sweep.rs:164: `fs::metadata` follows symlinks, so a symlinked blob is counted at its target's size, contradicting the comment at sweep.rs:160-163 which claims links are counted at the link's own size (`fs::symlink_metadata` would be needed for that). A store assembled with hard/sym links is measured against the wrong total for the ceiling.

🔵 `bug` services/proxy/src/config.rs:131: `CAIRN_SWEEP_INTERVAL` is validated for zero but `CAIRN_CACHE_MIN_AGE` is not, so `CAIRN_CACHE_MIN_AGE=0` silently disables the grace period that operations.md presents as protecting a package between pipeline jobs.
└ 4704 tok · 117.0 tok/s · 25K ctx · 2016ms ttft · 40.2s wall