diff --git a/internal/parse/claude.go b/internal/parse/claude.go
index 7dfc2f3..0e5e079 100644
--- a/internal/parse/claude.go
+++ b/internal/parse/claude.go
@@ -225,8 +225,10 @@ func updateClaude(ent *Entry, line []byte) {
 		if obj.Message == nil {
 			return
 		}
-		if obj.Message.Model != "" {
-			ent.Model = obj.Message.Model
+		// "<synthetic>" is the model id on system-generated messages; it
+		// must not displace the session's real model in the MODEL column
+		if m := obj.Message.Model; m != "" && m != "<synthetic>" {
+			ent.Model = m
 		}
 		if txt := firstUserText(obj.Message); txt != "" {
 			ent.LastText = truncRunes(collapseWS(txt), lastTextW)
diff --git a/internal/parse/entry.go b/internal/parse/entry.go
index 768d126..647dab0 100644
--- a/internal/parse/entry.go
+++ b/internal/parse/entry.go
@@ -7,9 +7,13 @@
 // weird line, just skip it.
 package parse
 
-// ParserV is bumped when parsers extract new fields: forces a one-time
-// rescan. It tracks the v1 PARSER_V so a v1 cache survives the upgrade.
-const ParserV = 6
+// ParserV is bumped when parsers extract new fields OR derive an existing
+// field differently: forces a one-time rescan. It tracks the v1 PARSER_V so
+// a v1 cache survives the upgrade. v7: title derivation changed (prompts,
+// not instruction files or path drops) and <synthetic> model ids are
+// ignored — cached v6 titles and models persist otherwise, since an
+// unchanged file is never rescanned.
+const ParserV = 7
 
 // Entry is one session file's accumulated state. The JSON tags match the
 // v1 Python cache exactly so ~/.cache/agentdash/usage.json round-trips
diff --git a/internal/parse/parse_test.go b/internal/parse/parse_test.go
index 48e4b0d..8a8561f 100644
--- a/internal/parse/parse_test.go
+++ b/internal/parse/parse_test.go
@@ -329,3 +329,46 @@ func TestStatusOf(t *testing.T) {
 	eq(t, "busy", StatusOf(&Entry{Mtime: now - 70, LastType: "user"}, 0, now, th), "busy?")
 	eq(t, "respawn", StatusOf(&Entry{Mtime: now - 10}, 4, now, th), "respawn ×4")
 }
+
+// A mixed-version cache: entries scanned by an older binary must be fully
+// rescanned by this one, or a derivation change (titles, model filtering)
+// never reaches files that stopped growing. This is the long-running-old-
+// watcher case: a stale `agentdash -w` kept rewriting v6 entries that the
+// upgraded binary then trusted forever.
+func TestOldParserVersionEntryIsRescanned(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "s.jsonl")
+	body := `{"type":"user","timestamp":"2026-01-01T00:00:00.000Z","message":{"content":"fix the exporter"}}` + "\n"
+	if err := os.WriteFile(path, []byte(body), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	c := NewCache()
+	// simulate an old binary's entry: fully scanned, junk title, stale V
+	st, _ := os.Stat(path)
+	c.Entries[path] = &Entry{Kind: "claude", V: ParserV - 1, Offset: st.Size(),
+		TitleUser: "# AGENTS.md instructions for /x"}
+	ent := ScanSession(path, c, "claude", tNow)
+	eq(t, "V", ent.V, ParserV)
+	eq(t, "TitleUser after rescan", ent.TitleUser, "fix the exporter")
+}
+
+// system-generated messages carry model "<synthetic>": it must not displace
+// the session's real model (a board row read "<syntheti…" in the MODEL column).
+func TestSyntheticModelDoesNotDisplaceReal(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "s.jsonl")
+	body := `{"type":"assistant","message":{"id":"m1","model":"claude-fable-5","usage":{"input_tokens":10}}}` + "\n" +
+		`{"type":"assistant","message":{"id":"m2","model":"<synthetic>","usage":{"input_tokens":5}}}` + "\n"
+	if err := os.WriteFile(path, []byte(body), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	ent := ScanSession(path, NewCache(), "claude", tNow)
+	eq(t, "Model", ent.Model, "claude-fable-5")
+
+	// a session with only synthetic messages reports no model at all
+	path = filepath.Join(t.TempDir(), "s2.jsonl")
+	body = `{"type":"assistant","message":{"id":"m1","model":"<synthetic>","usage":{"input_tokens":5}}}` + "\n"
+	if err := os.WriteFile(path, []byte(body), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	ent = ScanSession(path, NewCache(), "claude", tNow)
+	eq(t, "Model (synthetic only)", ent.Model, "")
+}