fix: point at the stores when a search finds an empty index

cmd/deja/empty_store_search_test.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// An empty store is not a query problem: "fewer words" cannot help when
+// nothing is indexed, and last, blame and the brief all say what to do
+// instead. Search is the command a new machine reaches for first (#832).
+func TestSearchOnAnEmptyStorePointsAtTheStores(t *testing.T) {
+	hermeticEnv(t)
+
+	out, err := captureRunStderr(t, "anything")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(out, "no agent history was found on this machine") {
+		t.Errorf("an empty machine still gets query advice:\n%s", out)
+	}
+	if strings.Contains(out, "try fewer words") {
+		t.Errorf("advice that cannot be followed is still printed:\n%s", out)
+	}
+
+	// With history indexed, an ordinary miss keeps the ordinary answer.
+	store := filepath.Join(os.Getenv("DEJA_CLAUDE_ROOT"), "-proj")
+	if err := os.MkdirAll(store, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	line := `{"type":"user","message":{"role":"user","content":"the hydraulic pump bearing failed"},"timestamp":"2026-07-01T10:00:00Z","sessionId":"a1","cwd":"/proj"}`
+	if err := os.WriteFile(filepath.Join(store, "a.jsonl"), []byte(line+"\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := captureRunStderr(t, "index"); err != nil {
+		t.Fatal(err)
+	}
+	miss, err := captureRunStderr(t, "zzzqqq")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(miss, "no matches in 1 indexed session") {
+		t.Errorf("an ordinary miss lost its answer:\n%s", miss)
+	}
+	if strings.Contains(miss, "no agent history") {
+		t.Errorf("a store with history was called empty:\n%s", miss)
+	}
+}

cmd/deja/main.go

@@ -647,6 +647,13 @@ func termCountLine(dir, q string) string {
 // their query missed. It fired on every ordinary miss, so the signature could
 // not be used to recognise the failure it was written for (#637).
 func printNoMatches(w io.Writer, dir, q string) {
+	// An empty store is not a query problem: "fewer words" cannot help when
+	// nothing is indexed, and `last`, `blame` and the brief all say what to do
+	// instead. Search is the command a new machine reaches for first (#832).
+	if n, err := index.SessionCount(dir); err == nil && n == 0 {
+		fmt.Fprintln(w, emptyIndexHint(fmt.Sprintf("no matches for %q", q)))
+		return
+	}
 	// Nothing to look up: very short tokens are dropped and punctuation is
 	// trimmed, so this query never reached the index. "Try fewer words"
 	// cannot be followed with one word, or none (#828). The message does not