fix(fuse,core): idle drain workers no longer spin while offline

Offline or paused, a drain worker claims nothing and then slept until the
earliest queued op fell due. Every queued op was already due and nothing
attempted it, so the wait was zero and all 16 workers spun on the queue
for the whole outage (issue #35: 17 min of CPU in 2 min 16 s).

A worker that claims nothing now sleeps the full idle poll; a reconnect
or resume wakes it. earliest_due_at also uses the claim's exclusions, so
an op held behind a claimed op on the same node no longer counts as due.

docs/BUGS.md B200.

docs/BUGS.md

@@ -101,6 +101,7 @@ a live account since.
 
 | Entry | Title |
 |---|---|
+| [B200](#b200--offline-with-changes-queued-the-daemon-keeps-several-cores-busy) | Offline with changes queued, the daemon keeps several cores busy |
 | [B198](#b198--switching-to-online-only-deletes-local-files-that-never-reached-drive) | Switching to online-only deletes local files that never reached Drive |
 | [B197](#b197--switching-to-online-only-trashes-synced-files-that-became-ignored) | Switching to online-only trashes synced files that became ignored |
 | [B196](#b196--one-unreadable-folder-stops-the-whole-synced-folder-from-syncing) | One unreadable folder stops the whole synced folder from syncing |
@@ -302,6 +303,33 @@ a live account since.
 
 Newest first.
 
+### B200 — Offline with changes queued, the daemon keeps several cores busy
+
+**Status:** Fixed, not verified live
+**Found:** 2026-10-09, issue #35: "offline, 3 queued", and systemd counted 17 minutes of CPU in
+2 m 16 s of wall time, 10 hours over a longer run.
+**Where:** `crates/pdfs-fuse/src/drain.rs`, `Core::run_pending_drain` and `idle_wait`;
+`crates/pdfs-core/src/db/ops.rs`, `Db::earliest_due_at`
+
+**Repro:** Queue a write, then cut the link (`nmcli networking off`). `pidstat -t -p $(pgrep -x
+pdfs) 5` shows the drain threads using most of several cores for as long as the outage lasts.
+
+**Cause.** Offline, a drain worker claims nothing, and then sleeps until the earliest queued op
+falls due. Every queued op was due already, and with no attempts nothing moves its
+`next_attempt_at`, so the sleep was zero. All 16 workers ran a query on every pass, the primary
+one its idle chores as well. The same spin happened online when a due op sat behind a claimed op
+on the same node, such as a rename queued behind a long upload: `earliest_due_at` counted it,
+`claim_next_due_op` skipped it.
+
+**Fix.** A worker that claims nothing, offline or paused, sleeps the full idle poll; a reconnect
+or a resume wakes it. `earliest_due_at` now uses the claim's own exclusions, one SQL fragment for
+both.
+
+**Test:** `drain::tests::an_offline_worker_waits_the_idle_poll_for_a_past_due_op`,
+`db::tests::earliest_due_at_skips_an_op_held_behind_a_claimed_one`.
+
+---
+
 ### B199 — A stopped share stays on the Shared by me page for minutes
 
 **Status:** Partly fixed. The share itself is still not deleted.