* fix(app): auto-set ref picker from a single attached PR
Attaching a PR in the new-workspace composer signals "I want this PR's
context", and almost always also means "base the worktree on this PR".
Until now the two paths were independent: the ref picker stayed on the
default branch, so the worktree was branched off main even though the
sidebar chip looked like a PR checkout.
Auto-promote the picker when exactly one PR is attached and the user
hasn't manually picked a ref. Manual picker selections are preserved;
auto-promoted ones are cleared when their backing attachment is removed.
* refactor(app): derive auto-promoted picker selection instead of syncing
The previous version drove `pickerSelection` from a useEffect that
inspected attachments and overwrote state. That meant the shared
`PickerSelection` type had to grow a `source: "manual" | "attachment"`
discriminator just so the effect could tell its own writes apart from
manual picks. Classic effect-as-derived-state.
Split the state instead. `manualPickerSelection` holds explicit picks;
`autoPickerItem` is a useMemo over composer attachments; the effective
`pickerSelection` is `manual ?? auto` via a small precedence helper. No
effect, no `source` flag, and `PickerSelection` stays a screen-local
shape since nothing outside needs it.
Deletes four screen-level .test.tsx files (2600+ lines of vi.mock + JSDOM
slop) and replaces each with verified coverage:
- sessions-screen.test.tsx: covered by archive-tab.spec.ts which exercises
the sessions screen via openSessions() with real agents
- workspace-draft-agent-tab.test.tsx: covered by new-workspace.spec.ts
"redirects to optimistic draft tab before agent creation resolves"
- new-workspace-screen.test.tsx: covered by new-workspace.spec.ts (main
submit, branch selection, PR selection, optimistic draft tab) plus
new-workspace-picker-item.test.ts (pickerItemToCheckoutRequest)
- project-settings-screen.test.tsx: covered by project-config-form.test.ts
(all round-trip string/array lifecycle semantics) and projects-settings.spec.ts
(save flow with passthrough field preservation)
Extracts syncPickerPrAttachment from new-workspace-screen.tsx into a new
pure module new-workspace-picker-state.ts with 5 zero-mock unit tests
covering: initial PR selection, branch selection without change, PR
replacement, PR removal on branch switch, and no-duplicate guard.
