Podcast: dedicated jetpack/v4 settings endpoint

[arcangelini]

Proposed changes

Move podcast site settings off core /wp/v2/settings (and, on Simple, off the legacy WPCOM v1.x site-settings filters) onto a dedicated, package-owned REST endpoint. This unifies the schema/sanitizers in one place and makes the feature work unchanged on self-hosted Jetpack — it's pure wp_options read/write with no wpcom backend.

• New endpoint Podcast_Settings_Endpoint — jetpack/v4/podcast/settings, manage_options gated.
  • GET returns the full, stable-shape record via Settings::get_all() (every option present; the two podcatcher maps padded to all directories).
  • PUT/POST/PATCH applies a partial patch: only keys present in the request are written, so absent keys can never clobber stored values. Array options merge on sanitize. Fires jetpack_podcast_settings_saved when an option is touched, then returns the full merged record.
• Settings — dropped show_in_rest from every register_setting() (defaults + sanitize_callbacks stay, so update_option() still merges/validates). Added get_all(), rest_schema_properties(), and empty_podcatcher_map() helpers. The podcasting_* keys no longer appear in core /wp/v2/settings.
• Tracks — the aggregate wpcom_podcasting_settings_saved event now fires off the new jetpack_podcast_settings_saved action instead of hooking the /wp/v2/settings REST response. The per-option update_option_* Tracks hooks are transport-independent and unchanged.
• Dashboard hook (use-podcast-settings.ts) — reads/writes the new endpoint via apiFetch with a shared module-level cache. The exported contract ({ data, isLoading } / { mutate, mutateAsync, isPending }) is unchanged, so all callers are untouched.
• Podcast Episode block — the show-cover read moves from /wp/v2/settings to the shared hook; for non-admin editors the fetch 403s and the cover resolves empty, identical to the prior behavior.

A follow-up in the wpcom repo (separate PR, to land after this deploys) removes the now-duplicate v1.x mu-plugin and the podcasting assertions in the core settings-controller test.

Does this pull request change what data or activity we track or use?

No new tracking. The existing wpcom_podcasting_settings_saved event is unchanged (same properties, same PII redaction of podcasting_email / podcasting_talent_name); only its trigger moved to a package action.

Testing instructions

• In the wp-admin Podcast dashboard, open Settings: confirm the form loads (a GET jetpack/v4/podcast/settings request returns the full padded record).
• Change one field and save: confirm the success snackbar, and that the saved value round-trips. Saving a partial change must not blank out other fields.
• Toggle a distribution URL and confirm podcasting_show_urls / podcasting_show_states persist and pad to all directories on reload.
• Confirm GET /wp/v2/settings no longer lists any podcasting_* keys.
• On a plain self-hosted Jetpack site, confirm the route registers and round-trips options with no WordPress.com connection.
• Package PHP tests: from projects/packages/podcast, run composer test-php (139 tests pass, incl. the new Podcast_Settings_Endpoint_Test).

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Verified locally: composer test-php (139 tests / 339 assertions, green), php -l, and phpcs on all changed files (clean). JS lint/type-check were not run locally (Node/pnpm toolchain mismatch in my env) and will be validated by CI.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (WordPress.com Site Helper), and enable the update/podcast-settings-jetpack-v4-endpoint branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack-mu-wpcom-plugin update/podcast-settings-jetpack-v4-endpoint

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 3 files.

File	Coverage	Δ%	Δ Uncovered
projects/packages/podcast/src/class-settings.php	160/182 (87.91%)	-8.86%	16 💔
projects/packages/podcast/src/class-podcast.php	9/24 (37.50%)	-1.63%	1 ❤️‍🩹
projects/packages/podcast/src/class-tracks.php	114/147 (77.55%)	-0.30%	-2 💚

1 file is newly checked for coverage.

File	Coverage
projects/packages/podcast/src/endpoints/class-podcast-settings-endpoint.php	38/43 (88.37%) 💚

Full summary · PHP report · JS report

_{If appropriate, add one of these labels to override the failing coverage check: Covered by non-unit tests Use to ignore the Code coverage requirement check when E2Es or other non-unit tests cover the code Coverage tests to be added later Use to ignore the Code coverage requirement check when tests will be added in a follow-up PR I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage.}