fix(maestro): spawn similar preselects the cloned project

Spawn similar dropped the session's cwd into the free-text directory hatch,
so the project picker showed nothing selected. For a worktree session that
cwd was the daemon-made checkout, and the worktree toggle defaulted on, so
the clone asked for a worktree of a worktree.

It now seeds the picker: the cloned project's box selected, the same
worktree decision, base repo plus '+ new' when the source had a worktree.
A seeded path that matches no project falls back to the raw input showing
that path instead of an empty picker.

web/src/spawnSimilar.ts

@@ -0,0 +1,30 @@
+// "Spawn similar" (#28): the seed a cloned session hands to a draft pane.
+// Pure — the caller owns opening the pane.
+
+import type { Draft } from "./layout.js";
+import type { Session } from "./types.js";
+
+/** Clone a session into draft values: same project, same command, same
+ *  worktree decision, fresh name.
+ *
+ *  A worktree session seeds its *base repository*, not the checkout the daemon
+ *  made for it: "similar" is another session of that project, and the daemon
+ *  never adopts an existing worktree (docs/WORKTREES.md), so seeding the
+ *  checkout would ask it to build a worktree out of a worktree. The picker
+ *  then lands on that repository's box with "+ new" active.
+ *
+ *  `cwdRawVisible: false` keeps the two-step project picker on screen with the
+ *  cloned project selected, instead of dropping the path into the free-text
+ *  escape hatch.
+ *
+ *  The name is left out on purpose: a clone is a new session and takes its own
+ *  generated handle. */
+export function spawnSimilarSeed(s: Session): Partial<Draft> {
+  const wt = s.worktree ?? null;
+  return {
+    command: s.command,
+    cwd: wt ? wt.base_repo : s.cwd,
+    worktreeEnabled: wt != null,
+    cwdRawVisible: false,
+  };
+}