feat(lanes): Antigravity lanes, release exited panes, fresh Codex starts

- antigravity: a third lane tool running Antigravity's `agy` CLI. `-i`
  carries the first prompt, `--continue` resumes; `agy` has no model,
  effort or permission flag, and `--dangerously-skip-permissions` is never
  emitted. No pipeline, no agents install, and no AI Router (native only,
  else EUNSUPPORTED). Add lane gains an Antigravity choice and the binary
  probe maps it to `agy`.
- UI: the lane card no longer renders a frame holding only a "Codex" chip,
  and the prompt box names the lane's CLI ("Ask Codex anything…"), via
  LANE_TOOL_LABEL.
- runs: a pane that exits is released on a 10 s server beat
  (healAllRunIds, DASHBOARD_RUN_HEAL_MS). Codex and Antigravity fire no
  hook, so their lanes stayed "running" until something re-read them.
- codex: Start no longer sends resumeLast — only "Resume last session"
  continues the previous thread.

server/lib/pty-run.js

@@ -19,7 +19,8 @@
  * the session (one-click Start/Resume) and is just one of possibly several
  * attached clients tmux already keeps in sync.
  *
- * Spawns `claude` or `codex` in the tmux pane based on the tool parameter.
+ * Spawns `claude`, `codex` or `agy` (Antigravity) in the tmux pane based on
+ * the tool parameter.
  *
  * A lane can hold up to four sessions, one per Workspace split pane: pane 0 is
  * `agenthub-lane-<laneId>` (the lane's own `run_id`), panes 1–3 are
@@ -55,7 +56,7 @@ const ALLOWED_PERMISSION_MODES = new Set([
 ]);
 // 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"]);
-const VALID_TOOLS = new Set(["claude", "codex"]);
+const VALID_TOOLS = new Set(["claude", "codex", "antigravity"]);
 const CODEX_SANDBOXES = new Set(["read-only", "workspace-write", "danger-full-access"]);
 const CODEX_APPROVALS = new Set(["on-request", "never"]);
 // Codex has no `--effort` flag; reasoning effort is a config override.
@@ -137,8 +138,23 @@ function buildCodexArgv({
   return argv;
 }
 
+/**
+ * Antigravity's `agy` has no model, effort or permission-mode flag, so only
+ * resume and the first prompt reach it. `-i` keeps the session interactive
+ * after that prompt (`-p` would print and exit). `--dangerously-skip-permissions`
+ * is never emitted, same rule as Codex's bypass flags.
+ */
+function buildAntigravityArgv({ resumeLast, initialPrompt }) {
+  const argv = ["agy"];
+  if (resumeLast) argv.push("--continue");
+  if (initialPrompt) argv.push("-i", initialPrompt);
+  return argv;
+}
+
 function buildArgv(args) {
-  return args.tool === "codex" ? buildCodexArgv(args) : buildClaudeArgv(args);
+  if (args.tool === "codex") return buildCodexArgv(args);
+  if (args.tool === "antigravity") return buildAntigravityArgv(args);
+  return buildClaudeArgv(args);
 }
 
 /**
@@ -258,7 +274,7 @@ function spawnRun(args) {
       // separate `external` row. Every run here is one interactive pane.
       mode: "interactive",
       cwd,
-      tool: tool === "codex" ? "codex" : "claude",
+      tool,
       model: model || null,
       permissionMode: permissionMode || "auto",
       effort: effort || null,