# Message scroller (`message-scroller`)

Chat transcript viewport — scrollable stack of message rows. Document order is chronological (newest last).

> **Layer:** L1 surface · **Recipe:** _(unset — see docs/agent/pick-a-surface.md)_
> Curriculum: `AGENTS.md` · pick matrix: `docs/agent/pick-a-surface.md` · blast radius: `CONSUMER_MAP.md`

> **Dialect:** Partial below is **unprefixed** (gallery / standalone HM). DOM contract Python often uses the **source token** `data-dz-*` / `dz-*` (Dazzle dual-lock). Match the CSS/JS bundle you load.

> **Demo vs contract:** Live gallery behaviour may use `/mock/*` or flash toasts. Those are **offline demos only** — implement **Server exchange** + **DOM contract**, not the mock. See AGENTS.md › Gallery demos.

## Copy this

```html
<div class="message-scroller" data-message-scroller role="log" aria-label="Conversation" aria-live="polite" tabindex="0">
  <div class="message" data-message data-from="in">
    <span class="message__media" aria-hidden="true">MR</span>
    <div class="message__body">
      <div class="message__meta"><span class="message__author">Maya Reyes</span><time class="message__time" datetime="2026-07-12T10:02">10:02</time></div>
      <div class="bubble" data-bubble data-from="in">
        <p>Can we reschedule the walkthrough to Thursday?</p>
      </div>
    </div>
  </div>
  <div class="message" data-message data-from="out">
    <span class="message__media" aria-hidden="true">You</span>
    <div class="message__body">
      <div class="message__meta"><span class="message__author">You</span><time class="message__time" datetime="2026-07-12T10:04">10:04</time></div>
      <div class="bubble" data-bubble data-from="out">
        <p>Thursday 14:00 works — I'll send a calendar hold.</p>
      </div>
    </div>
  </div>
  <div class="message" data-message data-from="in">
    <span class="message__media" aria-hidden="true">MR</span>
    <div class="message__body">
      <div class="message__meta"><span class="message__author">Maya Reyes</span><time class="message__time" datetime="2026-07-12T10:05">10:05</time></div>
      <div class="bubble" data-bubble data-from="in">
        <p>Perfect — see you then.</p>
      </div>
    </div>
  </div>
</div>
```

## Server exchange

This Hyperpart has **no server exchange** — presentation or client chrome only. If you put `hx-*` on a control that uses this markup, that action's exchange belongs to the action, not this part.

## Swap contract

Agent-visible HTMX topology (ADR-0054 / decision 0012). **Exchange envelope** = what the response may re-emit relative to the persistent slot (`body_only` | `outer` | `none` | `host_owned` | `document`). Dual-lock validates part markup only — not this envelope. Stem: `stems/morph-safe-hypermedia.md`.

**No host HTMX exchange** on this part — presentation or client chrome only. **Exchange envelope:** `n/a`.

If a **host** wraps this markup in `hx-*`, **that host owns the swap contract** (sole identity + envelope). Prefer `innerMorph` / `outerMorph` for stable slots; replacement for flash; body-only responses under inner swaps.

### Envelope response examples

What the **server returns** for each exchange. Match the **exchange envelope**; dual-lock still applies to interior markup.

This part has no owned exchange (envelope `n/a`). If a host adds `hx-*`, that host’s envelope applies — typically `body_only`:

```html
<!-- Prefer hx-swap=innerMorph into a stable body slot -->
<div class="dz-stack">content…</div>
```

Do **not** re-own the slot:

```html
<div id="message-scroller-root" data-dz-region>…</div>
```

## How to use it

No extended guidance authored yet — start from Copy this and the dependency chips.

### Seams

- copy the partial under Copy this; keep root class and data-* modifiers so the CSS/JS bundle matches
- no Server exchange on this part — pure presentation or client chrome
- satisfy the DOM contract tables (CI stop-ship)

## DOM contract

What emitted markup must satisfy (CI: `tests/test_contracts.py`). Do not invent attrs outside the tables. Python modules under `contracts/` are **package-internal dual-locks** (`from contracts._kit import …`) — not FastAPI business handlers. App servers implement **Server exchange** endpoints; this section constrains the HTML those endpoints return.

### `contracts/message_scroller.py`

- **Required root:** `.dz-message-scroller` (part `message_scroller`)

| Node | Attr | Constraint |
|---|---|---|
| `.dz-message-scroller` | `—` | — |

#### Module source

Monorepo dual-lock only — import `contracts._kit` from the HM package. Do not paste into app route modules.

```python
"""HYPERPART: message_scroller — chat transcript viewport (scrollable message stack).

Dual-lock unit is the scroller root. Message children, live-region attrs, and
scroll behaviour are host-owned. Class ``.dz-message-scroller`` is the stable
substrate root (FragmentRenderer: ``MessageScroller`` under ``display: conversation``).
"""

from contracts._kit import DomContract, Node

DOM_CONTRACT = DomContract(
    part="message_scroller",
    root=".dz-message-scroller",
    nodes=(Node(".dz-message-scroller", attrs={}),),
)

__all__ = ["DOM_CONTRACT"]
```

### `contracts/message.py`

- **Required root:** `.dz-message` (part `message`)

| Node | Attr | Constraint |
|---|---|---|
| `.dz-message` | `—` | — |

#### Module source

Monorepo dual-lock only — import `contracts._kit` from the HM package. Do not paste into app route modules.

```python
"""HYPERPART: message — chat message row (media + meta + bubble).

Dual-lock unit is the message root. Author/time, bubble body, and
``data-dz-from`` orientation are host-owned. Class ``.dz-message`` is the
stable substrate root (gallery CSS; Fragment ``Message`` +
``display: conversation`` emit the spine with nested ``Bubble``).
"""

from contracts._kit import DomContract, Node

DOM_CONTRACT = DomContract(
    part="message",
    root=".dz-message",
    nodes=(Node(".dz-message", attrs={}),),
)

__all__ = ["DOM_CONTRACT"]
```

### `contracts/bubble.py`

- **Required root:** `.dz-bubble` (part `bubble`)

| Node | Attr | Constraint |
|---|---|---|
| `.dz-bubble` | `—` | — |

#### Module source

Monorepo dual-lock only — import `contracts._kit` from the HM package. Do not paste into app route modules.

```python
"""HYPERPART: bubble — chat bubble content shell (inbound/outbound).

Dual-lock unit is the bubble root. Body copy and ``data-dz-from`` orientation
are host-owned. Class ``.dz-bubble`` is the stable substrate root (gallery CSS;
Fragment ``Bubble`` nests inside ``Message`` under ``display: conversation``).
Compose inside message rows for full chat UI.
"""

from contracts._kit import DomContract, Node

DOM_CONTRACT = DomContract(
    part="bubble",
    root=".dz-bubble",
    nodes=(Node(".dz-bubble", attrs={}),),
)

__all__ = ["DOM_CONTRACT"]
```

## Notes

PLACEHOLDER — shadcn parity (HMC-042). role=log + aria-live=polite for assistive updates. Auto-scroll-to-bottom controller deferred; prefer append-at-end + optional host scrollIntoView. Dual-lock root .dz-message-scroller (HMC-147).

## Source files

- `site/registry.py` (partial + exchanges + guidance)
- `contracts/message_scroller.py`
- `contracts/message.py`
- `contracts/bubble.py`