fix(run): stop Start/Resume from silently no-oping on an idle lane session

spawnRun adopted any existing `ccam-lane-<id>` tmux session without looking
at it, so a Resume issued while the session sat at a bare shell prompt (left
by `ccam lanes shell`, or by a `claude` that had already exited) dropped the
whole argv: no `--resume` ran, no initial prompt was typed, and the API still
answered 200. The lane's DB `run_id` is not set in that case, so the ERUNLIVE
guard in the start route never saw it either.

Reuse the pane instead of erroring: when the session exists and
`#{pane_current_command}` is a shell, type the argv into that pane and record
the run. A pane running a program (a live `claude`, an editor, a build) is
still adopted untouched, so attaching shows what is running rather than typing
over it. `sendCommand` POSIX single-quotes every argument and uses
`send-keys -l`, the only place in tmux.js that composes a command line.

server/lib/tmux.js

@@ -6,6 +6,9 @@
  * `tmux attach -t ccam-lane-<id>` (or `ccam lanes shell`). Never builds a
  * shell string — every call is `execFileSync("tmux", [...argv])` with an
  * explicit argument array (matches this repo's rule for git in worktree.js).
+ * The one place a command line is composed is `sendCommand`, which types into
+ * an existing pane's shell: there the shell IS the consumer, so every argument
+ * is POSIX single-quoted first and sent with `send-keys -l` (literal).
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -39,6 +42,36 @@ function newSession({ name, cwd, argv }) {
   execImpl(["new-session", "-d", "-s", name, "-c", cwd, "--", ...argv]);
 }
 
+/**
+ * The command currently running in the session's active pane (`bash`, `zsh`,
+ * `claude`, …). Null when tmux can't answer — callers treat that as "unknown,
+ * don't touch the pane".
+ */
+function paneCommand(name) {
+  try {
+    return (
+      execImpl(["display-message", "-p", "-t", name, "#{pane_current_command}"]).trim() || null
+    );
+  } catch {
+    return null;
+  }
+}
+
+/** POSIX single-quote escaping — the pane is a shell, so argv must be quoted. */
+function shellQuote(arg) {
+  return `'${String(arg).replace(/'/g, `'\\''`)}'`;
+}
+
+/**
+ * Type `argv` into an existing session's pane and press Enter. Only ever
+ * called when the pane sits at a shell prompt (see `paneCommand`); `-l` sends
+ * the string literally so no character is read as a tmux key name.
+ */
+function sendCommand(name, argv) {
+  execImpl(["send-keys", "-t", name, "-l", argv.map(shellQuote).join(" ")]);
+  execImpl(["send-keys", "-t", name, "Enter"]);
+}
+
 /** Idempotent — a session that's already gone is not an error. */
 function killSession(name) {
   try {
@@ -74,6 +107,8 @@ function isTmuxAvailable() {
 module.exports = {
   hasSession,
   newSession,
+  paneCommand,
+  sendCommand,
   killSession,
   listSessions,
   isTmuxAvailable,