Fix correctness bugs found by code review

- matrix: drop cryptohelper LoginAs so device.json creds aren't
  invalidated on every restart by Init's re-login
- matrix: thread ctx through PostThreadedReply; bot dispatcher derives
  per-command ctx from app lifecycle so SIGTERM cancels in-flight work
- matrix: isTokenValid verifies /whoami user_id matches configured one
- matrix: loadDevice distinguishes missing file from corrupt parse;
  refuse to silently overwrite a corrupt device.json
- matrix: Start checks Syncer type assertion and returns error
- arr: parseLookup skips empty-title items and extracts existing id
- bot: skip Add when Result.Exists; reply "already in library"

internal/bot/bot_test.go

@@ -44,7 +44,7 @@ type stubReplier struct {
 	calls    int
 }
 
-func (r *stubReplier) PostThreadedReply(_ id.RoomID, _ id.EventID, plain, htmlBody string) error {
+func (r *stubReplier) PostThreadedReply(_ context.Context, _ id.RoomID, _ id.EventID, plain, htmlBody string) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	r.calls++
@@ -53,6 +53,10 @@ func (r *stubReplier) PostThreadedReply(_ id.RoomID, _ id.EventID, plain, htmlBo
 	return nil
 }
 
+func newDispatcher(prefix string, services Services, replier Replier) *Dispatcher {
+	return New(context.Background(), prefix, services, replier)
+}
+
 const (
 	room   = id.RoomID("!room:example.org")
 	event  = id.EventID("$evt")
@@ -87,7 +91,7 @@ func TestDispatchMovieTopHit(t *testing.T) {
 		{Title: "Dune", Year: 1984},
 	}}
 	rep := &stubReplier{}
-	d := New("!", Services{Radarr: radarr}, rep)
+	d := newDispatcher("!", Services{Radarr: radarr}, rep)
 
 	d.Handle(room, event, sender, "!movie dune")
 
@@ -105,7 +109,7 @@ func TestDispatchMovieTopHit(t *testing.T) {
 func TestDispatchNoResults(t *testing.T) {
 	sonarr := &stubClient{}
 	rep := &stubReplier{}
-	d := New("!", Services{Sonarr: sonarr}, rep)
+	d := newDispatcher("!", Services{Sonarr: sonarr}, rep)
 
 	d.Handle(room, event, sender, "!tv obscure show")
 
@@ -119,7 +123,7 @@ func TestDispatchNoResults(t *testing.T) {
 
 func TestDispatchUnconfigured(t *testing.T) {
 	rep := &stubReplier{}
-	d := New("!", Services{}, rep)
+	d := newDispatcher("!", Services{}, rep)
 
 	d.Handle(room, event, sender, "!music radiohead")
 
@@ -131,7 +135,7 @@ func TestDispatchUnconfigured(t *testing.T) {
 func TestDispatchEmptyQuery(t *testing.T) {
 	radarr := &stubClient{}
 	rep := &stubReplier{}
-	d := New("!", Services{Radarr: radarr}, rep)
+	d := newDispatcher("!", Services{Radarr: radarr}, rep)
 
 	d.Handle(room, event, sender, "!movie")
 
@@ -149,7 +153,7 @@ func TestDispatchAddError(t *testing.T) {
 		addErr:  errors.New("boom"),
 	}
 	rep := &stubReplier{}
-	d := New("!", Services{Radarr: radarr}, rep)
+	d := newDispatcher("!", Services{Radarr: radarr}, rep)
 
 	d.Handle(room, event, sender, "!movie dune")
 
@@ -161,7 +165,7 @@ func TestDispatchAddError(t *testing.T) {
 func TestDispatchSearchError(t *testing.T) {
 	radarr := &stubClient{srchErr: errors.New("network down")}
 	rep := &stubReplier{}
-	d := New("!", Services{Radarr: radarr}, rep)
+	d := newDispatcher("!", Services{Radarr: radarr}, rep)
 
 	d.Handle(room, event, sender, "!movie dune")
 
@@ -172,7 +176,7 @@ func TestDispatchSearchError(t *testing.T) {
 
 func TestDispatchHelp(t *testing.T) {
 	rep := &stubReplier{}
-	d := New("!", Services{}, rep)
+	d := newDispatcher("!", Services{}, rep)
 
 	d.Handle(room, event, sender, "!help")
 
@@ -185,7 +189,7 @@ func TestDispatchHelp(t *testing.T) {
 
 func TestDispatchUnknown(t *testing.T) {
 	rep := &stubReplier{}
-	d := New("!", Services{}, rep)
+	d := newDispatcher("!", Services{}, rep)
 
 	d.Handle(room, event, sender, "!frobnicate stuff")
 
@@ -196,7 +200,7 @@ func TestDispatchUnknown(t *testing.T) {
 
 func TestNonCommandIgnored(t *testing.T) {
 	rep := &stubReplier{}
-	d := New("!", Services{}, rep)
+	d := newDispatcher("!", Services{}, rep)
 
 	d.Handle(room, event, sender, "just chatting")
 
@@ -205,10 +209,25 @@ func TestNonCommandIgnored(t *testing.T) {
 	}
 }
 
+func TestDispatchAlreadyInLibrary(t *testing.T) {
+	radarr := &stubClient{results: []arr.Result{{Title: "Dune", Year: 2021, Exists: true}}}
+	rep := &stubReplier{}
+	d := newDispatcher("!", Services{Radarr: radarr}, rep)
+
+	d.Handle(room, event, sender, "!movie dune")
+
+	if len(radarr.added) != 0 {
+		t.Fatalf("should not re-add existing item, got %d adds", len(radarr.added))
+	}
+	if !strings.Contains(rep.plain, "already has") || !strings.Contains(rep.plain, "Dune (2021)") {
+		t.Fatalf("unexpected reply: %q", rep.plain)
+	}
+}
+
 func TestCustomPrefix(t *testing.T) {
 	radarr := &stubClient{results: []arr.Result{{Title: "Dune", Year: 2021}}}
 	rep := &stubReplier{}
-	d := New(".bh ", Services{Radarr: radarr}, rep)
+	d := newDispatcher(".bh ", Services{Radarr: radarr}, rep)
 
 	d.Handle(room, event, sender, ".bh movie dune")