Introduce `NewsletterPage` as the shared shell for the modernized
dashboard: a single `Page` from `@wordpress/admin-ui` wraps a persistent
`Tabs.Root` from `@wordpress/ui` driven by a `?tab=` URL param so the
animated active-tab indicator slides between Subscribers and Settings
instead of remounting on each route hop. Switching tabs also strips the
subscriber-detail params (`subscriber`, `u`) so the inspector doesn't
hitchhike across to Settings.

The chrome polishes the page surface to match Forms: an off-white
background so cards stand out, a sticky page header without a bottom
rule, a sticky tab row pinned by a ResizeObserver-tracked CSS variable,
and a flex chain that lets DataViews fill the viewport on Subscribers
while letting Settings keep its content-tall scrolling model.

Hides the Subscribers tab when
`jetpack_wp_admin_subscriber_management_enabled` is filtered to false,
so hosts that defer subscriber management to Calypso land on a
Settings-only page.

Move the 9 settings sections, their state hooks, and the save handlers
into a new `NewsletterSettingsBody` component under
`src/settings/newsletter-settings.tsx`. The legacy
`NewsletterSettingsApp` becomes a thin chrome wrapper that mounts the
body inside `AdminPage` / `Container` / `Col` and runs the WP.com
connection check before passing `hasConnectedOwner` and `connectUrl`
in as props. The 9 sections themselves are unchanged.

The split lets the modernized dashboard mount the body inside its
`Tabs.Panel` without dragging `@automattic/jetpack-components` and
`@automattic/jetpack-connection` (and their SCSS chains) through the
wp-build pipeline. Snackbars dispatch straight to `@wordpress/notices`'s
`noticesStore` — the legacy chrome keeps its `<GlobalNotices />` for
surfacing, the wp-build polyfills' `SnackbarNotices` already covers the
modernized side.

Also switch `newsletter-section.tsx` to import `getRedirectUrl` via
the package's `./tools/jp-redirect` subpath, so dropping a section
into the wp-build bundle doesn't drag the rest of the components
package in with it.

Add a `./components/wpcom-support-link` export so consumers that only
need the support-link helper can import it without dragging the rest of
the components barrel — and crucially the SCSS-laden `Nudge` — through
their bundler. The Newsletter modernized dashboard switches its
categories section to the new subpath so the wp-build pipeline can
resolve the section without pulling in upgrade-nudge.

… its panel

Replace the inline `Page` chrome with `NewsletterPage` and feed both
tabs from the same `Tabs.Root`. `?tab=settings` flips to the Settings
panel, where `NewsletterSettingsBody` renders the existing 9-section
form unchanged on its legacy primitives — PR 5 will move those onto
WPDS `Card`. Subscribers stays the default and inherits the row-action
and header-action behaviour shipped in PR 3.

The route module gains `@automattic/jetpack-api`,
`@automattic/jetpack-shared-extension-utils`, and `@wordpress/url` so
the settings body and its sections — which import from those packages —
resolve once they're mounted inside the wp-build bundle. The inactive
panel renders `null` so we don't pay for the other view's data
fetching until a visitor opens it.

`route.inspector` decides visibility from search params alone, so a
deep-link like `?tab=settings&subscriber=123` would otherwise pop the
detail panel open on top of the Settings page. Bail out early when the
active tab is Settings; `NewsletterPage` already strips `subscriber`
and `u` on tab change, but this guard covers manual URL edits too.

…ssis

`@wordpress/route`'s `navigate` doesn't accept a search-updater
function, so passing `search: ( prev ) => ( ... )` no-ops the search
state — the new `?tab=` param never made it into the router and tabs
never switched. Pass an object literal instead, then read the active tab
from `search.tab` as before.

When `jetpack_wp_admin_subscriber_management_enabled` is filtered to
false the page is Settings-only, but the stage was still rendering two
`Tabs.Panel`s under a chrome that no longer wrapped them in a
`Tabs.Root`. That tripped the Base UI invariants
(`TabsRootContext is missing`, then `Tab/Panel count mismatch` once we
trimmed one Panel). Pin `activeTab` to `settings` when subscribers
are hidden and render `<NewsletterSettingsBody />` directly, with no
`Tabs.Panel` wrapper, so the Settings-only path never crosses the Tabs
primitive at all.

…e stage

`@wordpress/admin-ui`'s `Page` puts `overflow: auto` on the body
wrapper itself, so the body wrapper — not the outer stage — is the
scroll container. The page header is a sibling of the body wrapper,
not a parent. That meant the previous `top: var(--header-height)` on
`.jetpack-newsletter-page__tabs-row` was sticking the row 92px below
the body-wrapper top, leaving an empty band where the dataviews chrome
showed through. Switch the sticky offset to `top: 0` (the body
wrapper already starts directly under the page header) and drop the
`ResizeObserver` that fed `--jetpack-newsletter-header-height` —
nothing reads it anymore.

Admin-ui also sets `flex: 1 1 auto` on every direct child of the body
wrapper, which was outweighing the tabs-row's `flex-shrink: 0` and
collapsing it to ~24px so the 48px tab buttons clipped out of view.
Bump the tabs-row selector to mirror admin-ui's
`> :not(.admin-ui-page__header):not(.jetpack-footer) > *` path so
`flex: 0 0 auto` actually wins, and the bar grows to its natural
height with the active-tab indicator visible.

Subscribers ships header actions ("Add subscribers" + the More menu)
that pulled the header's title row to 36px, while Settings shipped no
actions and let the row collapse to its 28px text height — so swapping
tabs nudged the whole sticky row plus everything underneath by 8px.

Pin `.admin-ui-page__header > *:first-child` to a 36px min-height so
the title row matches the action-button height regardless of whether
actions are present. The 8px jump is gone, the tab bar no longer
re-positions on tab change.

Render `JetpackLogo` (mark only, no text) inline with "Newsletter"
in the page-header title slot, matching the wp-build chassis convention
that Forms, Backup, and VideoPress already use. The mark sits inside a
`Stack` with an 8px gap so the brand and the product name read as one
title unit, and the `ariaLabel` keeps the screen-reader name as plain
"Newsletter".

The logo arrives via the package's `./jetpack-logo` subpath so we
don't drag the rest of `@automattic/jetpack-components` (and its
SCSS chain) into the wp-build bundle.

The default header was leaving roughly 16px of slack between the
subtitle and the tab nav directly underneath, which read as a stray
band of empty page surface once the tab row was anchored to the body
wrapper. Pin `padding-block-end` on `.admin-ui-page__header` to
`--wpds-dimension-padding-xs` (4px) so the tab nav docks straight up
against the subtitle.

Move all 9 settings sections from `@wordpress/components`'s
`Card` / `CardHeader` / `CardBody` / `CardFooter` over to
`Card.Root` / `Card.Header` / `Card.Title` / `Card.Content` from
`@wordpress/ui`. `__experimentalHeading` (legacy heading inside the
header) becomes `Card.Title`; `__experimentalText` becomes WPDS
`Text`. Section internals — DataForm fields, save handlers, change
tracking — stay byte-for-byte identical.

WPDS `Card` doesn't ship a `Footer` slot, so the row that used to
live inside `<CardFooter>` becomes a `<div className="newsletter-card-footer">`
at the bottom of `<Card.Content>`. The shared style:
* save-button rows (Subscriptions, Newsletter categories, Sender
  settings, Welcome email) right-align via `justify-content: flex-end`,
* the Newsletter section's two-link row (Privacy + Manage subscribers)
  brackets via a `:has(> :nth-child(2))` rule that switches to
  `space-between` only when there's more than one child.

Save and action buttons (`Save`, `Add plans` / `Manage plans`) opt
into `__next40pxDefaultSize` so they ship the WordPress 7 default
height ahead of the upgrade. Pure refactor — no behaviour changes.

…elow

The settings body stacked its cards with `gap="md"` (12px), which
left them sitting too close together on the modernized chassis once
they got the new WPDS Card chrome. Switch the inner and outer
`Stack`s to `gap="xl"` so each card pair sits exactly 24px apart
via `--wpds-dimension-gap-xl` — same rhythm as the page-header
padding inset, no magic numbers.

Add a `padding-block-end` of `--wpds-dimension-padding-3xl` (32px)
to `.newsletter-settings` so the last card has room before the
page bottom on overflow scroll.

Replace the flat `ToggleWithEditorLink` rows in the Subscriptions card
with a 2×2 grid of `PlacementCard`s — overlay, modal, end-of-post,
floating button — each backed by its own SVG wireframe and an optional
"Preview and edit" link to the matching site-editor template part.
Navigation and Comments stay as inline `ToggleControl` subgroups
inside the same card so the whole subscription configuration reads
without scrolling between cards.

Telemetry catches up with the prototype:

* `jetpack_newsletter_placement_toggle` fires on every placement
  card flip, tagged with the placement slug + new value.
* `jetpack_newsletter_placement_preview_click` fires when the user
  clicks a card's preview link.
* `jetpack_newsletter_section_save` payload gains
  `changed_keys` / `change_count` so we can see what's actually in
  each user's batch instead of just the section name. The orchestrator
  will start passing the staged keys in the next commit.

The section accepts an optional `changedKeys` prop (still optional
for now so the orchestrator wiring lands separately without breaking
the build) and falls back to an empty array if the parent doesn't
supply it.

The legacy `NewsletterSection` doubled as a master `subscriptions`
toggle and a "send new posts as newsletters by default" toggle.
Now that the master toggle moves to the global Newsletter module
activation control, drop it from this UI and reshape the surviving
`wpcom_newsletter_send_default` field into a focused, email-themed
card called **Email defaults**.

While the section was being reshaped:

* Drop the "Privacy information" + "Manage all subscribers" footer
  links — they don't fit the email-defaults framing, and the latter is
  redundant with the Subscribers tab now living one click away.
* Rename the file to `sections/email-defaults-section.tsx` and the
  exported component to `EmailDefaultsSection`. Update
  `sections/index.ts` accordingly.

Reshuffle the IA in `newsletter-settings.tsx` to walk users from
activation flavour → distribution → email behaviour → categorisation:

  Paid → Subscriptions → Email defaults → Email content → Email byline
  → Email sender settings → Email reply-to settings → Welcome email →
  Newsletter categories.

Drop the always-editable wrapper around the deleted
`NewsletterSection`; everything now sits inside the same
`<Disabled isDisabled={ ! data.subscriptions }>` boundary that gates
the rest of the page on module status.

Subscriptions, Sender, Categories, and Welcome each fire a
`jetpack_newsletter_section_save` Tracks event when the user clicks
their Save button. Until now those events only carried the section
name — useful for counts but not for understanding which fields users
actually flip together inside a single batch.

Each section now accepts an optional `changedKeys: string[]` prop and
forwards it as `changed_keys` (comma-joined) + `change_count` on the
save event. The orchestrator wires it from the changeset state it
already maintains for each section's manual save (`subscriptionChanges`,
`senderNameChanges`, `newsletterCategoriesChanges`,
`welcomeEmailChanges` → `Object.keys()`).

Every Jetpack site now lands on the unified Subscribers/Settings
chassis we've been building since PR 1. The legacy `AdminPage`
chrome stays in the bundle behind the same filter, so hosts that
need the old surface back can opt out with
`add_filter( 'rsm_jetpack_ui_modernization_newsletter', '__return_false' );`
until the legacy code paths are removed in a follow-up.

The unified Newsletter page now owns the Subscribers tab, so neither
the wp-admin Subscribers submenu nor the "Subscribers ↗" Calypso
link belongs in the sidebar anymore.

* `modules/subscriptions.php`: drop the `add_subscribers_menu`
  method (and its `jetpack_admin_menu` hook) that registered the
  Calypso shortcut on self-hosted, plus the `Subscribers_Dashboard`
  init that registered the standalone wp-admin Subscribers page on
  hosts with `jetpack_wp_admin_subscriber_management_enabled` on.
  Drop the now-unused `Admin_Menu` and `Redirect` imports.
* `jetpack-mu-wpcom/wpcom-admin-menu.php`: collapse the
  `// Jetpack > Subscribers.` if/else into a single
  `wpcom_hide_submenu_page` call — the Calypso link no longer surfaces
  here either way, but we keep the hide so anything else that adds it
  back stays out of the sidebar. Drop `Subscribers_Dashboard` import
  and remove `'subscribers'` from the Jetpack submenu order list.

Newsletter is now the single Subscribers entry point. The
`subscribers-dashboard` package will be deleted in the next commit.

Now that no plugin instantiates `Subscribers_Dashboard` (the previous
commit retired both call sites), the package has no consumers and can
go. Delete `projects/packages/subscribers-dashboard/` outright.

Pull the `automattic/jetpack-subscribers-dashboard` dep out of
`plugins/jetpack/composer.json`, `packages/jetpack-mu-wpcom/composer.json`,
and `packages/masterbar/composer.json` (none of those packages were
using it directly), refresh the Jetpack plugin's `composer.lock` and
the workspace `pnpm-lock.yaml` so the autoload classmap and pnpm
graph stop carrying the package. Standalone `Subscribers` page is
fully retired — Newsletter is the single Subscribers entry now.

Record a tracks event whenever the visitor flips to a different tab —
`{ site_type, tab }`. The guard skips the no-op case where
`next === activeTab`, so refreshes and same-tab nav don't pollute the
counts. Analytics is already initialized at the page Stage (PR 2), so
the event reaches Tracks immediately on first interaction.

PR 2 lifted analytics initialization to the page Stage but
`load_admin_scripts` was still short-circuiting before any script
enqueue ran when modernization was on. `analytics.initialize` queues
events into `window._tkq`, but without the Tracks transport
(`stats.wp.com/w.js`) loaded, the queue grows forever and no
`pixel.wp.com/t.gif` requests fire — telemetry from PR 6's new
`jetpack_newsletter_tab_view` event went nowhere.

Move the `jp-tracks` enqueue above the modernized short-circuit so
it runs on both surfaces; everything else (the legacy
`jetpack-newsletter` bundle, JetpackScriptData, etc.) stays gated to
the legacy path.