Stop cache eviction in progress at shutdown (closes #102)

StartEviction runs the eviction goroutine with its own context, which
StopEviction cancels in place of the old stop channel, so a pass in
progress stops at its next database call, file, row or eviction
candidate instead of running to completion. StopEviction takes a
context: when it ends before the goroutine exits, StopEviction stops
waiting and returns an error wrapping it. The handlers' stop hook
passes fx's stop context, so an eviction still running at fx's stop
deadline fails the stop and the exit code is 1. The contextcheck
suppression on the start hook stays, with a one-line reason: the loop
outlives OnStart.

Model: opus-5-5

TODO.md

@@ -29,6 +29,14 @@ P2: security: referer blacklist
 
 # Completed Steps
 
+- 2026-10-04 shutdown stops cache eviction in progress (closes #102):
+  `StartEviction` runs the eviction goroutine with its own context, which
+  `StopEviction` cancels, so a pass in progress stops at its next database
+  call, file, row or eviction candidate instead of running to completion;
+  `StopEviction` takes a context and, when that context ends before the
+  goroutine exits, stops waiting and returns its error; the handlers' stop hook
+  passes fx's stop context, so an eviction still running when fx's stop
+  deadline ends fails the stop and makes the exit code 1.
 - 2026-10-03 shutdown sets the exit code and waits for image processing
   (closes #86): fx alone handles SIGINT and SIGTERM, and the server's own
   signal handler is gone; fx's `Run` in `cmd/pixad` exits with the shutdown's