Feature summary

The new-session dialog already has a "Use worktree" toggle (per-repo for
collection projects, nice). Two gaps make it painful in practice:

1. The toggle does not persist. Every new session starts back at the
   default (worktree on), so I have to flip every repo every time.
2. There is no way to set a default checkout strategy on a project
   (especially collection projects) or app-wide.

What problem are you trying to solve?

I'm working on a collection project with 13 Azure Terraform AVM repos. Most
of my sessions want main-folder checkout (lightweight tasks, "install a
skill" sessions, read-only PR reviews, work that needs to persist into the
real checkout). A handful want worktree isolation.

Today, for every new session I have to:

• Open the per-repo branch picker for each of the 13 repos
• Flip the "Use worktree" toggle off on each
• Then start the session

Confirmed via data.db that the strategy is stored per-workspace in
workspaces.workspace_type only. There's no checkout_strategy column on
projects, no relevant key in settings.json or config.json, and the
toggle state isn't remembered between sessions.

A second, related pain point: artifacts I put into a worktree folder
(installing agents/skills into .github\ of a member repo, for example)
live in an ephemeral path. When the workspace is archived, the work is
effectively lost unless I remembered to mirror it into the main checkout.

Proposed solution

Any one of these would help, ideally all three:

1. Remember the last toggle state per project (and per repo within a
   collection project) so the next new-session dialog opens with my
   previous choices preselected.
2. Project-level default: a setting on the project (especially
   collection projects) that defines the default checkout_strategy for
   new sessions, applied to all member repos but still overridable in the
   dialog.
3. App-wide default in Settings: a fallback default for any project
   without its own override.

Workflow impact

• For my 13-repo collection, every new session today requires flipping
  13 toggles before I can even start working. A persisted choice or a
  project default removes that friction entirely.
• Power users who prefer worktree isolation per session keep full
  per-session control via the existing toggle.
• Aligns expectations with IDE-extension users (work lands in their real
  checkout by default).

Installation context

• App version: v0.2.23
• OS: Windows 11
• Project type: collection (13 Azure Terraform AVM repos)
• Container kind: collection, current checkout strategy: worktree_set

Additional context

The "Use worktree" toggle in the new-session dialog (per-repo for
collection projects) is exactly the right UX primitive. The gap is purely
persistence + defaults.

Related issues, each covering a different slice of the worktree story but
none asking for toggle persistence + project-level default:

• Decouple sessions from worktrees: support multiple sessions per branch and worktrees from existing branches #169 — Decouple sessions from worktrees
• Configurable worktree location instead of centralized path #407 — Configurable worktree location
• Customize worktree checkout #463 — Customize worktree checkout (sparse)