Key-binding doesn't work as expected, "nnoremap <leader>td $F)i, args2<ESC>"

Question

nnoremap <leader>td $F)i, args2<ESC>

---

# base string
test ----> (args1)

# expected string after <leader>td
test ----> (args1, args2)

# real result string 
test ----> (args1)

The above are the key-map and what I expect with the key-map. However, the result is that the cursor is stopped the end of the string not entering insert mode. When I simulate the key-map, typing keys in the <leader>td by hand, it works.

In addition, The more wired thing is the below. After appending a character at the end of the string, It works as expected.

# base string, I append ':' character at the end of the string
test ----> (args1):

# real result string, it works !!!?
test ----> (args1, args2):

What have I missed?

Answer 1

From :h map-error:

                                                        *map-error*
Note that when an error is encountered (that causes an error message or beep)
the rest of the mapping is not executed.  This is Vi-compatible.

In your mapping, if the F command fails to find a closing parenthesis, Vim will stop processing the rest of the {rhs}.

If you want Vim to ignore a possible error, you could use the :silent command, followed by the ! argument. From :h :sil:

When [!] is added, error messages will also be
skipped, and commands and mappings will not be aborted
when an error is detected.

Here's how you could rewrite your mapping, using the :normal command to type the keys from the command line, prefixed by :silent to ignore any error:

nno  <silent>  <leader>td  :<c-u>sil! norm! $F)i, args2<cr>