applies-switch: tab label shows only one badge when an applies-item combines multiple deployment types #4627

Describe the bug

When an {applies-item} argument combines several deployment-type keys — the pattern the applies-switch syntax docs recommend — the rendered tab label shows only one badge. The last key in source order wins, and the other deployment types are invisible in the tab bar:

• ::::{applies-item} { serverless:, ech: } renders a tab labeled only ECH. There is no Serverless badge anywhere in the tab bar.
• ::::{applies-item} { self:, ece:, eck: } renders a tab labeled only ECK.
• Live example: on High JVM memory pressure, { ess:, ece: } renders only ECE, and { self:, eck: } renders only ECK.

Combining different badge families is not affected: { stack: ga 9.4+, serverless: ga } renders both badges (related: #1976, which fixed ordering and separators for that case).

In the generated HTML, the applies-switch-label contains a single <applies-to-popover badge-key="ECH" …> element, so the other keys are dropped before badge rendering rather than hidden by styling. Reproduced with docs-builder 1.68.0 locally and confirmed on the published site (see the live example above).

Why it matters

Readers find their tab by their deployment type. On a page whose tabs render as "ECH | ECK", a serverless or self-managed user concludes their deployment isn't covered, even though the markup covers it — a reviewer of elastic/docs-content#8151 flagged exactly that. The only workaround today is splitting the grouped item into one applies-item per deployment type and duplicating the content.

Expected behavior

The tab label shows one badge per deployment type in the definition — for example Serverless ECH and Self-managed ECE ECK — matching how the same definitions render as {applies_to} badges elsewhere.

Steps to reproduce

Build a page containing:

::::{applies-switch}

:::{applies-item} { serverless:, ech: }
Content for Serverless and ECH
:::

:::{applies-item} { self:, ece:, eck: }
Content for self-managed, ECE, and ECK
:::

::::

The tabs render as "ECH" and "ECK".

Tooling

• docs-builder
• migration tooling
• I'm not sure