HTTP API: 404 for a chat id the list of chats leaves out (closes #5)

The chat client keeps contact records that GET /api/v1/chats does not
list, such as the bot's own profile (1 on a new profile) and a contact
it creates itself (2), and reads or sends in them when asked. The
message endpoints now look the id up, through chatID in
internal/api/chats.go, in the same list the chats endpoint answers
with, and answer 404 for any id not in it. The webhook endpoints can
call chatID too.

Model: opus-5-5

internal/api/api_test.go

@@ -29,12 +29,14 @@ const (
 var errChat = errors.New("sqlite: database is locked at /var/lib/simplexcalc")
 
 // fakeClient stands in for the chat client. It answers with contacts,
-// items or sent, or with err, and remembers what it was asked.
+// items or sent, or with an error: contactsErr from Contacts, err from
+// the others. It remembers what it was asked.
 type fakeClient struct {
-	contacts []simplex.Contact
-	items    []simplex.ChatItem
-	sent     simplex.ChatItem
-	err      error
+	contacts    []simplex.Contact
+	items       []simplex.ChatItem
+	sent        simplex.ChatItem
+	contactsErr error
+	err         error
 
 	userID, contactID int64
 	count             int
@@ -48,7 +50,7 @@ func (f *fakeClient) Contacts(
 	f.userID = userID
 	_, f.hadDeadline = ctx.Deadline()
 
-	return f.contacts, f.err
+	return f.contacts, f.contactsErr
 }
 
 func (f *fakeClient) ChatItems(
@@ -269,7 +271,7 @@ func TestHeaders(t *testing.T) {
 		{&fakeClient{}, chatsPath, bearer},
 		{&fakeClient{}, chatsPath, ""},
 		{&fakeClient{}, "/nothing", bearer},
-		{&fakeClient{err: errChat}, chatsPath, bearer},
+		{&fakeClient{contactsErr: errChat}, chatsPath, bearer},
 	} {
 		rec := request(t, newAPI(credential, tc.client),
 			http.MethodGet, tc.path, tc.auth)