perf(awards): release the logbook snapshot once it goes cold

Opening the Awards panel pulls every QSO into a cached slice and kept it for the rest of the session: the cache was only ever invalidated by a logbook change, never by disuse. Each cached QSO is a 1896-byte struct plus its strings AND a decoded map of its ADIF extras - one map allocation per QSO. Harmless at 30k rows, several hundred megabytes at 132k, which is where it was reported. A janitor drops it after 15 minutes without a reader and calls FreeOSMemory, because Go hands pages back lazily and the whole point is that the operator sees the memory return. 15 minutes is deliberately generous: an awards session recomputes every few seconds and re-pulling a large remote logbook costs seconds. The heap size is now logged when the snapshot is built and when it is released - a memory report was unanswerable without a number.

app.go

@@ -11,6 +11,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"runtime/debug"
 	"sort"
 	"strconv"
@@ -688,6 +689,7 @@ type App struct {
 	awardSnapMu        sync.Mutex  // guards the award QSO snapshot
 	awardSnap          []qso.QSO   // light-scanned + enriched logbook snapshot reused across award computations
 	awardSnapRev       string      // logbook revision the snapshot was built at ("" = none)
+	awardSnapUsed      time.Time   // last read — the snapshot is dropped once it goes cold (see awardSnapshotJanitor)
 	dataDir            string      // <exeDir>/data — holds config.json, logs, cty.dat
 
 	// shuttingDown gates beforeClose re-entry: the first user attempt to
@@ -1235,6 +1237,7 @@ func (a *App) startup(ctx context.Context) {
 	// behind telnet).
 	a.clusterEvents = newClusterQueue()
 	go a.clusterEventWorker()
+	go a.awardSnapshotJanitor() // give the award snapshot's memory back once it goes cold
 
 	a.cluster = cluster.NewManager(
 		// onSpot / onLine run on the session's socket-read goroutine, so they must
@@ -4172,6 +4175,7 @@ func (a *App) awardSnapshot() ([]qso.QSO, error) {
 		a.awardSnapMu.Lock()
 		if a.awardSnap != nil && a.awardSnapRev == rev {
 			qs := a.awardSnap
+			a.awardSnapUsed = time.Now()
 			a.awardSnapMu.Unlock()
 			return qs, nil
 		}
@@ -4187,18 +4191,63 @@ func (a *App) awardSnapshot() ([]qso.QSO, error) {
 	}); err != nil {
 		return nil, err
 	}
-	applog.Printf("awardSnapshot: pulled %d qsos from logbook in %v (rev=%s)",
-		len(all), time.Since(t0).Round(time.Millisecond), rev)
+	// Heap alongside the row count: this snapshot is the single largest thing
+	// OpsLog holds, and "OpsLog is eating memory" reports are unanswerable
+	// without a number. A 132 000-QSO logbook was the case that prompted it.
+	var ms runtime.MemStats
+	runtime.ReadMemStats(&ms)
+	applog.Printf("awardSnapshot: pulled %d qsos from logbook in %v (rev=%s) — go heap now %d MB",
+		len(all), time.Since(t0).Round(time.Millisecond), rev, ms.HeapAlloc/(1024*1024))
 
 	if revErr == nil {
 		a.awardSnapMu.Lock()
 		a.awardSnap = all
 		a.awardSnapRev = rev
+		a.awardSnapUsed = time.Now()
 		a.awardSnapMu.Unlock()
 	}
 	return all, nil
 }
 
+// awardSnapIdleTTL is how long the snapshot survives without a reader.
+//
+// Generous on purpose: an operator working through the Awards panel triggers a
+// computation every few seconds, and re-pulling costs seconds on a big remote
+// logbook. This is only meant to catch the far commoner case — awards looked at
+// once, then hours of logging with several hundred megabytes still held.
+const awardSnapIdleTTL = 15 * time.Minute
+
+// awardSnapshotJanitor drops the award snapshot once nothing has read it for a
+// while, and returns the memory to the OS.
+//
+// The snapshot is a whole logbook of QSO structs, each carrying a decoded map of
+// its ADIF extras: ~1.9 KB of struct plus strings and one map allocation per
+// QSO. At 30 000 QSOs that is tens of megabytes and nobody notices; at 132 000
+// it is several hundred, held for the rest of the session because the cache had
+// no expiry — only invalidation when the logbook changed.
+func (a *App) awardSnapshotJanitor() {
+	for {
+		time.Sleep(time.Minute)
+		a.awardSnapMu.Lock()
+		n := len(a.awardSnap)
+		idle := !a.awardSnapUsed.IsZero() && time.Since(a.awardSnapUsed) > awardSnapIdleTTL
+		if a.awardSnap != nil && idle {
+			a.awardSnap = nil
+			a.awardSnapRev = ""
+		}
+		a.awardSnapMu.Unlock()
+		if n > 0 && idle {
+			// FreeOSMemory, not just GC: Go hands pages back lazily, and the whole
+			// point here is that the operator sees the memory come back.
+			debug.FreeOSMemory()
+			var ms runtime.MemStats
+			runtime.ReadMemStats(&ms)
+			applog.Printf("awardSnapshot: released %d cached qsos after %v idle — go heap now %d MB",
+				n, awardSnapIdleTTL, ms.HeapAlloc/(1024*1024))
+		}
+	}
+}
+
 // GetAwardStats computes the worked/confirmed/validated reference counts of one
 // award, broken down by band and by mode category (All/CW/Digital/Phone).
 func (a *App) GetAwardStats(code string) (AwardStatsResult, error) {