Unify response processing and add hx-multipart extension

[scriptogre]

Organize ctx, and give requests and streaming extensions one swap path, one action path, and one lifecycle.

Public API

Canonical response context

event.detail.ctx = {
  request: { /* fetch options */ },
  response: { raw, status, headers },
  swap: { content, target, style, select, selectOOB, /* modifiers */ },
  actions: { trigger, pushUrl, replaceUrl, /* custom HX-* actions */ }
}

• ctx.swap replaces flat ctx.target, ctx.swap, ctx.select, ctx.text, and related swap fields.
• ctx.actions replaces separate history and response-header state. HX-Toast becomes actions.toast for extensions.
• ctx.status is removed. Queue admission is tracked internally as run, queued, or dropped.

Positional htmx.swap()

await htmx.swap(html, '#messages', { style: 'beforeend' })

This replaces htmx.swap({ text, target, swap, ... }) and is closer to what we had in htmx 2.0.

Shared server actions

api.runActions({ trigger: 'saved', toast: 'Done' }, element, { ctx })

• Adds htmx:before:actions and htmx:after:actions.
• Adds actions to htmx.ajax() options. push and replace remain shorthands.
• Status rules, response headers, normal requests, and streaming parts use the same executor.
• History events no longer include detail.response, because actions can run without a response.

Explicit response lifecycle

before:request → after:request → before:response → after:response → swap → done

• after:request means fetch resolved. The body is still unread.
• after:response exposes the body as ctx.swap.content.
• done replaces finally:request and fires once an admitted pipeline ends.
• Bundled extensions, types, upgrade checks, and docs follow these semantics.

hx-multipart

New extension for streaming hypermedia, alongside hx-sse and hx-ws.

<div hx-multipart:connect="/events"></div>

Content-Type: multipart/mixed; boundary=x

--x
Content-Type: text/html
HX-Target: #status

Connected
--x--

One Fetch response can now stream ordered multipart/mixed parts through same swap and action APIs.

Brings a few public API changes for which I'd create an hx-htmx-4-beta-compat extension, which should be quite lightweight.