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/pty-run.js

@@ -9,6 +9,10 @@
  * out-of-band (crash, manual `tmux kill-session`, host reboot) self-corrects
  * on the next read instead of leaving a ghost "running" row.
  *
+ * Start/Resume is create-or-reuse: when the lane's tmux session already
+ * exists but its pane sits at a shell prompt, the argv is typed into that
+ * pane instead of being dropped on the floor by a silent adopt.
+ *
  * Every session is named `ccam-lane-<laneId>` so a real terminal can attach
  * to the exact same session (`tmux attach -t ccam-lane-<id>`, or
  * `ccam lanes shell`) — that's the whole point: the dashboard both creates
@@ -30,6 +34,8 @@ try {
 const RUN_ID_RE = /^ccam-lane-(\d+)$/;
 const EFFORT_LEVELS = new Set(["low", "medium", "high", "xhigh", "max"]);
 const ALLOWED_PERMISSION_MODES = new Set(["acceptEdits", "default", "plan", "bypassPermissions"]);
+// Pane commands that mean "idle shell prompt, safe to type a command into".
+const SHELL_COMMANDS = new Set(["sh", "bash", "zsh", "fish", "dash", "ksh", "csh", "tcsh"]);
 
 function runIdForLane(laneId) {
   return `ccam-lane-${laneId}`;
@@ -99,31 +105,44 @@ function spawnRun(args) {
 
   const id = runIdForLane(laneId);
   const startedAt = Date.now();
+  const argv = buildArgv({ model, permissionMode, effort, resumeSessionId, initialPrompt });
+
+  const record = () => {
+    if (!dashboardRuns) return;
+    dashboardRuns.recordRun({
+      id,
+      sessionId: resumeSessionId || null,
+      mode: null,
+      cwd,
+      model: model || null,
+      permissionMode: permissionMode || "acceptEdits",
+      effort: effort || null,
+      resumeSessionId: resumeSessionId || null,
+      prompt: initialPrompt || "",
+      status: "running",
+      startedAt,
+      endedAt: null,
+      exitCode: null,
+      laneId,
+    });
+  };
 
   if (!tmux.hasSession(id)) {
-    const argv = buildArgv({ model, permissionMode, effort, resumeSessionId, initialPrompt });
     tmux.newSession({ name: id, cwd, argv });
-    if (dashboardRuns) {
-      dashboardRuns.recordRun({
-        id,
-        sessionId: resumeSessionId || null,
-        mode: null,
-        cwd,
-        model: model || null,
-        permissionMode: permissionMode || "acceptEdits",
-        effort: effort || null,
-        resumeSessionId: resumeSessionId || null,
-        prompt: initialPrompt || "",
-        status: "running",
-        startedAt,
-        endedAt: null,
-        exitCode: null,
-        laneId,
-      });
-    }
+    record();
+  } else if (SHELL_COMMANDS.has(tmux.paneCommand(id) || "")) {
+    // The session exists but its pane is sitting at a bare shell prompt — a
+    // `ccam lanes shell`, or a `claude` that already exited. Adopting it
+    // silently here would swallow the whole request: a Resume would spawn no
+    // `--resume` and an initial prompt would never be typed, while the API
+    // still answered 200. Run the argv in the pane the user already sees
+    // instead of erroring or opening a second session.
+    tmux.sendCommand(id, argv);
+    record();
   }
-  // Already running: adopt silently, same convention as this repo's server
-  // port-adoption logic — no error, no duplicate session.
+  // Pane is running something (a live `claude`, an editor, a build): adopt
+  // silently, same convention as this repo's server port-adoption logic — no
+  // error, no duplicate session. Attaching shows the user what is running.
 
   return getRun(id);
 }