Fix regression on paste in non-interactive read

As reported in
https://github.com/fish-shell/fish-shell/issues/11836#issuecomment-3369973613,
running "fish -c read" and pasting something would result this error
from __fish_paste:

	commandline: Can not set commandline in non-interactive mode

Bisects to 32c36aa5f8 (builtins commandline/complete: allow handling
commandline before reader initialization, 2025-06-13).  That commit
allowed "commandline" to work only in interactive sessions, i.e. if
stdin is a TTY or if overridden with -i.

But this is not the only case where fish might read from the TTY.
The notable other case is builtin read, which also works in
noninteractive shells.
Let's allow "commandline" at least after we have initialized the TTY
for the first reader, which restores the relevant historical behavior
(which is weird, e.g. « fish -c 'read; commandline foo' »).

CHANGELOG.rst

@@ -12,6 +12,7 @@ This release fixes the following regressions identified in 4.1.0:
 - Stopped printing output that would cause a glitch on old versions of Midnight Commander (:issue:`11869`).
 - Added a fix for some configurations of Zellij where :kbd:`escape` key processing was delayed (:issue:`11868`).
 - Fixed a case where the :doc:`web-based configuration tool <cmds/fish_config>` would generate invalid configuration (:issue:`11861`).
+- Fixed a case where pasting into ``fish -c read`` would fail with a noisy error (:issue:`11836`).
 - Fixed a case where upgrading fish would break old versions of fish that were still running.
 
   In general, fish still needs to be restarted after it is upgraded,

src/builtins/commandline.rs

@@ -635,7 +635,7 @@ pub fn commandline(parser: &Parser, streams: &mut IoStreams, args: &mut [&wstr])
         transient = parser.libdata().transient_commandline.clone().unwrap();
         current_buffer = &transient;
         current_cursor_pos = transient.len();
-    } else if is_interactive_session() {
+    } else if parser.interactive_initialized.load() || is_interactive_session() {
         current_buffer = &rstate.text;
         current_cursor_pos = rstate.cursor_pos;
     } else {

src/builtins/complete.rs

@@ -458,7 +458,7 @@ pub fn complete(parser: &Parser, streams: &mut IoStreams, argv: &mut [&wstr]) ->
             None => {
                 // No argument given, try to use the current commandline.
                 let commandline_state = commandline_get_state(true);
-                if !is_interactive_session() {
+                if !parser.interactive_initialized.load() && !is_interactive_session() {
                     streams.err.append(cmd);
                     streams
                         .err