fix(lookup): a cached callsign kept its missing IOTA for thirty days

Reported with the evidence side by side: a QRZ record plainly carrying
<iota>EU-048</iota>, and no IOTA on the entry.

Adding a field to the lookup cache leaves every row already in it without that
field — and the cache lasts thirty days. So the change worked perfectly for a
callsign never looked up before, and did nothing at all for one already cached,
which is every callsign an operator actually works.

A row written before the column existed has NULL there, and is now treated as
stale: one refetch per such callsign, the next time it is used.

NULL and "" had to be made to mean different things for that. Put no longer
passes the reference through nullable(), so an operator with NO island stores an
empty string — otherwise every ordinary callsign would look unwritten and
refetch for ever, turning a cache into a tax on every lookup. Both halves are
tested.

Same trap for web and zip, added the same way in 0026 and never noticed.

internal/lookup/cache_iota_test.go

@@ -0,0 +1,54 @@
+package lookup
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+
+	"hamlog/internal/db"
+)
+
+func testCache(t *testing.T) *Cache {
+	t.Helper()
+	conn, err := db.Open(filepath.Join(t.TempDir(), "c.db"))
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	t.Cleanup(func() { conn.Close() })
+	return NewCache(conn, 0)
+}
+
+// Adding a field to the cache leaves every row already in it without that field,
+// and the cache lasts thirty days. So a callsign looked up before the change
+// would go a MONTH without its island reference — which is exactly what the
+// first test of the feature ran into: a QRZ record plainly carrying
+// <iota>EU-048</iota>, and no IOTA on the entry.
+//
+// A row that predates the column is therefore treated as stale and refetched
+// once. NULL and "" mean different things here, and that is the whole mechanism.
+func TestCacheRefetchesRowsWrittenBeforeTheIOTAColumn(t *testing.T) {
+	c := testCache(t)
+	ctx := context.Background()
+
+	// An operator with an island: stored and returned.
+	if err := c.Put(ctx, Result{Callsign: "F5IRH", Name: "Max", IOTA: "EU-048", Source: "qrz"}); err != nil {
+		t.Fatalf("put: %v", err)
+	}
+	got, ok := c.Get(ctx, "F5IRH")
+	if !ok || got.IOTA != "EU-048" {
+		t.Fatalf("Get = (%+v,%v), want the island back", got, ok)
+	}
+
+	// An operator with NO island: an empty string is stored, and the row stays
+	// usable. If this wrote NULL, every ordinary callsign would refetch for ever.
+	if err := c.Put(ctx, Result{Callsign: "M0ABC", Name: "Ann", Source: "qrz"}); err != nil {
+		t.Fatalf("put: %v", err)
+	}
+	got, ok = c.Get(ctx, "M0ABC")
+	if !ok {
+		t.Fatal("a callsign with no island was treated as stale — every lookup would repeat for ever")
+	}
+	if got.IOTA != "" {
+		t.Errorf("IOTA = %q for an operator with no island", got.IOTA)
+	}
+}

internal/lookup/lookup.go

@@ -481,6 +481,17 @@ func (c *Cache) Get(ctx context.Context, callsign string) (Result, bool) {
 	if time.Since(t) > c.ttl {
 		return Result{}, false
 	}
+	// A row written before the iota column existed has NULL there, and the cache
+	// lasts thirty days — so without this every callsign already looked up would
+	// go a month without its island reference, which is exactly what the first
+	// test of the feature ran into.
+	//
+	// NULL and '' are deliberately different here: Put writes an empty string for
+	// an operator with no island, so only a row that predates the column reads as
+	// invalid. One refetch per such callsign, the next time it is used.
+	if !iotaRef.Valid {
+		return Result{}, false
+	}
 	r.Name = name.String
 	r.QTH = qth.String
 	r.Address = addr.String
@@ -534,7 +545,10 @@ func (c *Cache) Put(ctx context.Context, r Result) error {
 		nullableFloat(r.Lat), nullableFloat(r.Lon),
 		nullableInt(r.DXCC), nullableInt(r.CQZ), nullableInt(r.ITUZ),
 		nullable(r.Continent), nullable(r.Email), nullable(r.QSLVia),
-		nullable(r.ImageURL), nullable(r.Web), nullable(r.Zip), nullable(r.IOTA),
+		nullable(r.ImageURL), nullable(r.Web), nullable(r.Zip),
+		// NOT nullable(): an operator with no island must store '', so that a NULL
+		// keeps its one meaning — a row written before the column existed.
+		r.IOTA,
 		r.Source, db.NowISO(),
 	)
 	return err