fix(maestro): cap and centre the spawn form's width

The form filled the full pane width, so on a 4K display every input
stretched thousands of pixels wide. Bound it to 60ch (in line with the
48ch/42ch precedents already in the type scale) and centre it with
margin auto; panes narrower than the cap still fill edge to edge.

flake.nix

@@ -125,7 +125,7 @@
             pnpmDeps = (pkgs.fetchPnpmDeps.override { pnpm = pkgs.pnpm_10; }) {
               inherit (finalAttrs) pname version src;
               fetcherVersion = 3;
-              hash = "sha256-Lhi41AtCK69SM4+7zih19+Njf7o2hyXrAV0W6VO9YxU=";
+              hash = "sha256-D9JdgI92vzAY8en2zGEEPd4hwOLVi3sr1joT4b17Be4=";
             };
 
             buildPhase = ''

web/src/multiview.test.ts

@@ -147,6 +147,48 @@ describe("multiview openDraft (#62)", () => {
     expect((mv.el.querySelector(".mv-draft input[name=name]") as HTMLInputElement).value).toBe("wip");
   });
 
+  it("reuses an already-synced empty pane instead of splitting (#72)", async () => {
+    const layout = emptyLayout();
+    const tab = layout.tabs[0];
+    const first = splitLeaf(tab, "", "s1", "row", true);
+    const empty = splitLeaf(tab, first, null, "row", true);
+    tab.focusedLeafId = empty;
+    const mv = makeMv(layout);
+    document.body.appendChild(mv.el);
+    mv.render();
+    // Let the mounted form's loadProjects() settle and auto-sync its picked
+    // defaults into leaf.draft before openDraft runs (#72's dead-branch window).
+    await flush();
+    expect(leaves(tab.root).find((l) => l.id === empty)?.draft).not.toBeNull();
+
+    mv.openDraft();
+    await flush();
+
+    expect(leaves(tab.root)).toHaveLength(2);
+    expect(tab.focusedLeafId).toBe(empty);
+  });
+
+  it("keeps a seed after reusing an already-synced empty pane (#72)", async () => {
+    const layout = emptyLayout();
+    const tab = layout.tabs[0];
+    const first = splitLeaf(tab, "", "s1", "row", true);
+    const empty = splitLeaf(tab, first, null, "row", true);
+    tab.focusedLeafId = empty;
+    const mv = makeMv(layout);
+    document.body.appendChild(mv.el);
+    mv.render();
+    await flush();
+
+    mv.openDraft({ cwd: "/home/user/proj", command: "claude" });
+    await flush();
+
+    const leaf = leaves(tab.root).find((l) => l.id === empty)!;
+    expect(leaf.draft?.cwd).toBe("/home/user/proj");
+    expect(leaf.draft?.command).toBe("claude");
+    const cwdRaw = mv.el.querySelector(".mv-draft .cwd-raw") as HTMLInputElement;
+    expect(cwdRaw.value).toBe("/home/user/proj");
+  });
+
   it("seeds a clone's cwd and command into the draft", async () => {
     const layout = emptyLayout();
     const mv = makeMv(layout);

web/src/multiview.ts

@@ -423,9 +423,15 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
       return;
     }
     const target = findLeaf(tab.root, tab.focusedLeafId)!;
-    if (!target.sessionId && !target.draft) {
-      // An already-empty pane becomes the draft in place.
+    if (!target.sessionId) {
+      // Empty = no session, not `!draft` (#72): the mounted form auto-syncs
+      // picked defaults into `draft` once ready, so that's never reliably null.
       target.draft = draft();
+      const stale = draftForms.get(target.id);
+      if (stale) {
+        stale.destroy();
+        draftForms.delete(target.id);
+      }
     } else {
       // Split a fresh draft beside the focused pane.
       tab.focusedLeafId = splitLeaf(tab, target.id, null, "row", true);

web/src/styles.css

@@ -1215,6 +1215,9 @@ textarea {
 /* ---------- forms ---------- */
 
 .spawn-form {
+  width: 100%;
+  max-width: 60ch;
+  margin: 0 auto;
   padding: var(--sp-3);
   overflow: auto;
   display: flex;