NEXUS-4029: Add task source references and primary controls - #1889

…a channel (#2512)

## TL;DR

Adds `conversation.ui.Conversation`, a public host-owned scope that lets
a plugin's own `ui.Message` rows and `ui.Composer` for one channel get
native Edit, confirmed Delete with recovery and retry, and host media
review. Mounting it never marks anything read, follows a thread or
enters the channel visit. Cross-channel overview cards need this; today
a bare `ui.Message` row has neither Edit nor Delete, and `ui.Thread`
always visits.

Fixes NEXUS-4193

## How it works

`ui.Conversation({ session, scope, channelId, channelName?, threadId?,
children(interactions) })` renders the existing `ConversationChannel` in
its host-dialog, non-visiting mode (`host` plus `active={false}`). Inbox
Drafts already uses this mode internally. Inside it:

- `MessageManagement` supplies the row menu's Edit/Delete under the
existing permission checks, the delete confirmation and the
failed/unconfirmed recovery notice.
- `MessageEditScope` makes Edit target the `ui.Composer` in the same
scope. A scope without a composer offers no Edit, as in other previews.
- `ConversationHost` owns media review and panel overlays, focus return,
and the existing stale-session guard (nothing opens once the relay
snapshot is no longer this ready session).

`children` receives the host's `onOpenLink`, `canOpenLink` and
`onOpenMediaReview` to pass to the rows. `EmbeddedThread` and the new
scope now share one `HostedChannel` wrapper, so `ui.Thread` behavior is
unchanged. No changes to `MessageManagement`, `ConversationHost`,
`MessageComposer` or `contracts.ts`.

## Evidence

`src/features/conversation/EmbeddedConversation.test.tsx` mounts two
fictional channel cards (real relay session, real `ui.Message` rows and
`ui.Composer` from `ConversationService`; only `MediaReviewViewer` is
reduced, since it has its own suites). It covers:

- the same rows without the scope have no Edit/Delete; inside it, each
card offers both
- mount, background presentation, re-present and unmount never call
`enterChannel`, `leaveChannel`, `follow`, `markMessageRead`,
`markChannelRead` or the roster's `profiles.reserve`, and publish
nothing
- Edit fills only that card's composer and publishes a kind-40003 edit
tagged with that card's channel. The other card's message is untouched.
- Delete: cancel publishes nothing; confirm publishes kind 5; a relay
rejection shows the recovery notice in that card only; Retry resends the
same event id and the row goes away
- media review opens with the card's channel and message, and stops
opening after the session stops being ready

Fail-then-pass: with `active={false}` removed from the scope, all 4
tests fail (`enterChannel` and `profiles.reserve` are called). The scope
restored, all pass.

The packed `@buzz/author` consumer fixture
(`tests/fixtures/conversation-consumer`) now renders its rows and
composer inside `ui.Conversation` and passes `interactions.onOpenLink`
to its rows. So the generated declarations must export the new component
and its `children(interactions)` type, and the existing
`conversation.spec.mjs` journey mounts it in the real app. The fixture
type-checks against freshly built declarations. As a negative control, a
misspelled interactions field fails `tsc`.

Run on a Linux Blox box on base `a34ba4f` (the local host-build guard
refused under load):
- `vitest run src/features/conversation
src/features/messages/MessageManagement.test.tsx
src/bundled/inbox/DraftsView.test.tsx`: 19 files, 221 tests passed
- `tsc --noEmit` and `biome check --error-on-warnings` on the touched
files: clean
- `pnpm author:build`, packed and installed into a copy of the consumer
fixture, then `pnpm build` (`tsc`): clean

No browser journeys were added or removed. The existing consumer journey
now mounts the scope; it runs only in hosted CI, not locally. Focus,
overlay and native-edit geometry are unchanged existing
`ConversationHost`/composer behavior that existing suites already cover.

## Limits and coordination

- Not exercised in the native desktop app or a browser journey. Hosted
CI runs the full suites.
- Two `ui.Conversation`s for the same channel each show that channel's
recovery notice, because recovery is per channel. The docs say to render
one per channel or card.
- No overlap in hunks or behavior with #2483 (Solo list arrangement/row
action in `service.tsx`), #1889, #2306 or #2303 (`contracts.ts`), #2083
(`MessageManagement.tsx`) or #2167 (`ConversationHost.tsx`). This PR
does not edit `contracts.ts`, `MessageManagement.tsx` or
`ConversationHost.tsx`.
- This PR doesn't adopt the scope in any plugin. That is separate work.

## Initiative context

[Buzz Threads
status](https://g2.sqprod.co/apps/kylez-buzz-threads-status)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Signed-off-by: Kyle Zemek <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>