daemon: add test-send subcommand, flatten newlines in send_prompt

test-send calls send_prompt() directly for debugging tmux delivery.
Flatten newlines to spaces in literal mode to prevent premature
input submission.

Co-Authored-By: ProofOfConcept <poc@bcachefs.org>

src/bin/poc-daemon/main.rs

@@ -116,6 +116,11 @@ enum Command {
         /// Value to set (omit to query)
         value: Option<f64>,
     },
+    /// Send a test message to the Claude pane
+    TestSend {
+        /// Message to send
+        message: Vec<String>,
+    },
     /// Dump full internal state as JSON
     Debug,
     /// Shut down daemon
@@ -256,6 +261,17 @@ async fn client_main(cmd: Command) -> Result<(), Box<dyn std::error::Error>> {
                     req.get().set_seconds(seconds.unwrap_or(300));
                     req.send().promise.await?;
                 }
+                Command::TestSend { message } => {
+                    let msg = message.join(" ");
+                    let pane = {
+                        let reply = daemon.status_request().send().promise.await?;
+                        let s = reply.get()?.get_status()?;
+                        s.get_claude_pane()?.to_str()?.to_string()
+                    };
+                    let ok = crate::tmux::send_prompt(&pane, &msg);
+                    println!("send_prompt(pane={}, ok={}): {}", pane, ok, msg);
+                    return Ok(());
+                }
                 Command::Afk => {
                     daemon.afk_request().send().promise.await?;
                     println!("marked AFK");