Themes "with-theme": fix free .org theme install hanging after signup

[taipeicoder]

Proposed Changes

• Fix a free .org theme installed via the with-theme signup flow hanging on a blank "Putting the pieces together" screen after signup. getWithThemeDestination sends .org themes to the same marketplace install page as free plugins (/marketplace/theme/:theme/install/:site), which only initiates the atomic transfer + install when the in-memory purchase-flow handoff is present. That handoff doesn't survive the full-page redirect out of signup, so the page polled the site indefinitely. The redirect is now marked trusted (?directInstall=1) so the install page initiates the transfer/install itself.

Why are these changes being made?

This is the theme counterpart of the free-plugin install hang already fixed for the with-plugin flow — the two flows route to the same install page, and the install page already reads directInstall for theme installs (its init effect handles wpOrgTheme), so this is a one-line parity fix.

Testing Instructions

1. Log out, start the with-theme flow with a free .org theme and a paid plan in the cart.
2. Complete account + domain + plan → checkout.
3. Confirm the post-checkout install completes (transfer + theme install) instead of hanging on "Putting the pieces together".

No unit test added: getWithThemeDestination is not exported and has no existing coverage (its siblings mock the function rather than exercise it); the directInstall mechanism it relies on is already shipped and exercised via the free-plugin path.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• For UI changes, have you tested the affected components in dark mode?
• Have you tested accessibility for your changes?
• Have you used memoizing on expensive computations?
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

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[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~1 bytes added 📈 [gzipped])

Details

name                      parsed_size           gzip_size
signup                          +16 B  (+0.0%)       +1 B  (+0.0%)
async-step-unified-plans        +16 B  (+0.0%)       +1 B  (+0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.