upwatch: hold a seeding torrent app for one line test, then put its limit back exactly (R-1250)

When the agent waits for quiet and qBittorrent or Transmission runs: record the limit first,
hold at 1 KiB/s, ask the agent for a test on request, put the old limit back (deferred; a
household change during the test stays). Start-up puts back a limit a killed controller left;
the 50 % rule skips while a hold record exists. Commit only.

CHANGELOG.md

@@ -1,3 +1,27 @@
+## Unreleased (next: v0.343.0) — the line test for a box that seeds all day (R-1250) (2026-10-24) — committed, not released
+
+**MinAgent: 0.158.1** (unchanged): an agent before 0.165.0 never reports `waiting_for_quiet`, so nothing is held. Attended
+brief 2026-10-24, Part 4 (commit only; the release rides the next normal train). Design: felhom.eu `08` §9.
+
+- **`internal/upwatch/linehold.go`** — when the agent says a test is due and waits only for quiet, and qBittorrent (or
+  Transmission) runs: read the app's upload limit exactly as it stored it, write the record
+  `upwatch.line_test_hold` FIRST, hold the app at 1 KiB/s (Transmission: 1 kB/s, limit on), call the agent's
+  `POST /host/line-test/run` (about 55 s), then put the old limit back — the household's own included — and clear the
+  record. The release is deferred (a panic puts it back too); a hold whose write failed is undone before anything else;
+  a household change made during the test stays; an app that cannot be read keeps the record, and no new hold starts
+  until it is put back. `startUpwatch` puts back a limit a killed controller left (`RecoverHold`) before any rule runs,
+  and each 15-minute tick runs the hold before qBittorrent's 50 % rule, which skips while a record exists (it would
+  read 1 KiB/s as the household's change and stop for good).
+- **`agentapi.LineTestRun`** + `LineTestState.WaitingForQuiet`; `postSlow` gives one call its own timeout (2 min) on the
+  pinned transport — the client's 15 s would cut the 55 s answer.
+- **Transmission**: `rpc` (Basic auth + the session-id handshake) shared by `Ask` and the new `ReadLimit`/`WriteLimit`
+  (`session-get`/`session-set` of `speed-limit-up` + `speed-limit-up-enabled`); a `result` other than success is an error.
+- Tests (each seen failing): `TestHold_PutsTheHouseholdsLimitBackExactly` (measured, failed, refused, agent unreachable),
+  `…PutsBackNoLimit`, `…StartupPutsBackALimitLeftHeld`, `…APanicInTheTestStillPutsTheLimitBack`,
+  `…AHouseholdChangeDuringTheTestStays`, `…AFailedHoldIsUndoneAndNoTestRuns`, `…AnUnreachableAppKeepsTheRecordUntilItIsBack`,
+  `…OnlyWhenTheAgentWaitsAndAnAppRuns`, `…QBLimitRuleSkipsAHeldLimit`, `…TheTwoAppsReadAndWriteTheirLimit`,
+  `TestLineTestRunOutlastsTheClientTimeout`, `TestStartUpwatchRecoversTheHoldFirst`, `TestUpwatchHoldGetsBothAgentCalls`.
+
 ## v0.342.0 (2026-10-24) — RELEASED on the operator's yes (attended release run; image sha256:d002d3b7…, from `42cda07`, CI 2283) — the upload and CPU watch, the tested line and qBittorrent's limit
 
 **MinAgent: 0.158.1** (unchanged). **Hub dependency:** the four new event types need hub 0.169.0 (committed the same