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.

client/src/components/run/RunSetup.tsx

@@ -56,6 +56,7 @@ import type {
   CcMdItem,
 } from "../../lib/api";
 import type { Session, LaneTool } from "../../lib/types";
+import { LANE_TOOL_LABEL } from "../../lib/types";
 import { Select } from "../Select";
 
 export interface SlashCommand {
@@ -430,10 +431,13 @@ export function RunSetup(props: RunSetupProps) {
               </div>
             )}
           </Field>
-          <Field label={t("fields.model")}>
-            <ModelPicker value={props.model} onChange={props.onModelChange} tool={props.tool} />
-          </Field>
-          {props.tool === "codex" ? (
+          {/* `agy` takes no model, permission or effort flag. */}
+          {props.tool !== "antigravity" && (
+            <Field label={t("fields.model")}>
+              <ModelPicker value={props.model} onChange={props.onModelChange} tool={props.tool} />
+            </Field>
+          )}
+          {props.tool === "antigravity" ? null : props.tool === "codex" ? (
             <>
               <Field label={t("fields.sandbox")}>
                 <Select<CodexSandbox>
@@ -472,17 +476,19 @@ export function RunSetup(props: RunSetupProps) {
               />
             </Field>
           )}
-          <Field label={t("fields.effort")}>
-            <Select<EffortLevel>
-              value={props.effort}
-              onChange={props.onEffortChange}
-              options={RUN_EFFORT_CHOICES.map((c) => ({
-                value: c.id,
-                label: c.label,
-                hint: c.hint,
-              }))}
-            />
-          </Field>
+          {props.tool !== "antigravity" && (
+            <Field label={t("fields.effort")}>
+              <Select<EffortLevel>
+                value={props.effort}
+                onChange={props.onEffortChange}
+                options={RUN_EFFORT_CHOICES.map((c) => ({
+                  value: c.id,
+                  label: c.label,
+                  hint: c.hint,
+                }))}
+              />
+            </Field>
+          )}
         </div>
         <div className="flex shrink-0 items-center rounded-md border border-border bg-surface-2 p-0.5 text-[11.5px]">
           <Seg
@@ -542,9 +548,9 @@ export function RunSetup(props: RunSetupProps) {
           value={props.prompt}
           onChange={props.onPromptChange}
           onSubmit={() => handleStart(props)}
-          placeholder={t("fields.promptPlaceholderTerminal")}
+          placeholder={t("fields.promptPlaceholderTerminal", { tool: LANE_TOOL_LABEL[props.tool] })}
           rows={5}
-          slash={props.tool !== "codex"}
+          slash={props.tool === "claude"}
           fileCwd={props.resumeSession?.cwd || props.cwd}
         />
         <div className="mt-1 text-[10px] text-fg-muted">
@@ -609,18 +615,18 @@ export function RunSetup(props: RunSetupProps) {
 function handleStart(props: RunSetupProps, session?: Session) {
   const resume = session ?? props.resumeSession;
   const codex = props.tool === "codex";
+  const agy = props.tool === "antigravity";
   props.onStart({
     laneId: props.laneId,
     // A resume is pinned to its own session's folder — that's what the locked
     // cwd field shows, so it's what gets sent.
     cwd: resume?.cwd || props.cwd || undefined,
-    model: props.model || undefined,
-    permissionMode: codex ? undefined : props.permissionMode || undefined,
+    model: agy ? undefined : props.model || undefined,
+    permissionMode: codex || agy ? undefined : props.permissionMode || undefined,
     sandbox: codex ? props.sandbox : undefined,
     approval: codex ? props.approval : undefined,
-    effort: props.effort || undefined,
-    resumeSessionId: codex ? undefined : resume?.id || undefined,
-    resumeLast: codex && !resume ? true : undefined,
+    effort: agy ? undefined : props.effort || undefined,
+    resumeSessionId: codex || agy ? undefined : resume?.id || undefined,
     // A resume continues a session that already has its own history — sending
     // whatever is sitting in the prompt box would fire an extra turn nobody
     // asked for, so a resume carries no prompt at all.