feat(bestie): pin the saved Bestie DM - #1935

## Problem

`main` CI is red: all four `JavaScript (n/4)` jobs fail at `tsc
--noEmit` (e.g. run 41491229758 on `baeefef1e`):

```
src/bundled/bestie/PinnedBestie.test.tsx(560,11): error TS2739: ... is missing the following properties from type 'PageNavigation': position, savePosition
```

## Cause

Semantic merge conflict between two PRs that were each green on their
own:

- #1960 (`dd898a7c6`) made `position(key)` and `savePosition(key,
value)` required members of `PageNavigation`
(`src/features/navigation/service.ts`) so pages can restore the reader's
place on Back.
- #1935 (`baeefef1e`, pin the saved Bestie DM) added a hand-built
`PageNavigation` stub in `PinnedBestie.test.tsx` that was written
against the older shape.

## Fix

Add `position: () => undefined` and `savePosition() {}` to the stub.
This is the same no-op stub used by the other page tests (e.g.
`src/bundled/agents/AgentsPage.test.tsx:678`). Test-only change, no
production code touched. Pinned Bestie doesn't use saved positions, so a
no-op stub keeps the test's behavior as-is.

## Validation

- `bin/pnpm exec tsc --noEmit`: clean
- `bin/pnpm exec vitest run src/bundled/bestie/PinnedBestie.test.tsx`:
14/14 pass
- Pre-commit hooks (biome, icons, literal-names, sadscan) pass

Not run locally: the full Vitest shards and browser suites. This PR's CI
covers those.

Signed-off-by: Kalvin Chau <[email protected]>
Co-authored-by: hax <[email protected]>

Ports Clay's Choose your bestie from #1935's pre-revert head f789630: with
no saved Bestie, the Bestie page offers the viewer's eligible agents and the
shared New agent dialog in place of Builderlab's hosted setup. The plugin
keeps registering the stack's Bestie tabs, check-in cleanup and
onBestieMade alongside the page.

Co-authored-by: Clay Delk <[email protected]>

Co-authored-by: eggboy <3986e5374b8c11a274f4a53fa9a68e1e18b53e712f8aa5218add2485bf5a2b09@buzz.block.builderlab.xyz>
Co-Authored-By: Claude Opus 5.5 <[email protected]>
Signed-off-by: Riley Crane <[email protected]>

Ports Clay's Choose your bestie from #1935's pre-revert head f789630: with
no saved Bestie, the Bestie page offers the viewer's eligible agents and the
shared New agent dialog in place of Builderlab's hosted setup. The plugin
keeps registering the stack's Bestie tabs, check-in cleanup and
onBestieMade alongside the page.

Co-authored-by: Clay Delk <[email protected]>

Co-authored-by: eggboy <3986e5374b8c11a274f4a53fa9a68e1e18b53e712f8aa5218add2485bf5a2b09@buzz.block.builderlab.xyz>
Co-Authored-By: Claude Opus 5.5 <[email protected]>
Signed-off-by: Riley Crane <[email protected]>

Ports Clay's Choose your bestie from #1935's pre-revert head f789630: with
no saved Bestie, the Bestie page offers the viewer's eligible agents and the
shared New agent dialog in place of Builderlab's hosted setup. The plugin
keeps registering the stack's Bestie tabs, check-in cleanup and
onBestieMade alongside the page.

Co-authored-by: Clay Delk <[email protected]>

Co-authored-by: eggboy <3986e5374b8c11a274f4a53fa9a68e1e18b53e712f8aa5218add2485bf5a2b09@buzz.block.builderlab.xyz>
Co-Authored-By: Claude Opus 5.5 <[email protected]>
Signed-off-by: Riley Crane <[email protected]>

## Why

The pinned Bestie DM from #1935 needs a clear starting point when no
Bestie is saved. The old page instead launches a separate Builderlab
setup flow. This replaces that path with one chooser for existing agents
and new agents.

## What

- Explain what a bestie means, then offer a searchable picker with
avatars, names, and distinct identity labels.
- Open the picker below its field, capped at roughly four avatar rows,
with search above scrollable results.
- Reuse **Create agent**, save the choice to the account, and open the
canonical DM.
- Keep remote agents eligible, but ask before saving: “Some bestie
features aren’t available with remote agents.” Cancel leaves the choice
unchanged and keeps any newly created agent.
- Show the chooser in place when the saved agent is gone, and clear the
account choice after completed deletion.

## How

The chooser uses `session.agentChoices`, the shared creation dialog, the
existing `main-agent` record, and the pinned DM from #1935. It adds no
messaging path or remote capability setup. The shared Combobox gains an
opt-in compact popup; other callers keep their current behavior.

Deletion checks the current account record before writing `agent: null`.
Native signing now admits that cleared value. Existing browser journeys
retain their plugin/default and navigation contracts with the new
heading; browser cases added/removed: **0/0**. The retired hosted-setup
UI assertions are replaced by mounted chooser/save/recovery coverage.

## Risk

This removes the separate Builderlab-specific Bestie onboarding, not
Builderlab agent creation. The remote warning does not turn on memory or
check-ins. Account cleanup is a read/replace, not an atomic
compare-and-swap: another device's choice in that gap can be
overwritten. A cleanup error reports that deletion completed but the
Bestie choice could not be cleared.

## Testing

Clay tried the running native app and iterated on the empty-state copy,
searchable picker, and popup size/placement. The remote confirmation was
opened through the production chooser in an isolated Chromium fixture
with a sample hosted agent; no real agent was created or account choice
saved.

Still deferred: live Builderlab creation → confirmation → account save →
DM; deletion and reload persistence on the rebased head; native
remote-warning focus behavior; and the full light/dark, viewport, and
enlarged-text acceptance pass. These checks remain outstanding; this PR
does not claim completed acceptance.

## Bigger picture

#1935, Riley’s Bestie tab (#2034), and its memory switch (#2035) are
merged. This branch includes main through `23338bc84`, preserving both
alongside the empty-state chooser.

**Overlap with Riley's #2047:** both replace the empty Bestie page and
clear a deleted choice. This PR contains the chooser UI Clay tested
today. Riley's PR sits above the Bestie settings/memory/check-in stack,
restricts Bestie to local agents, and wires selection into that setup.
This PR deliberately allows remote agents with a warning. The tab and
memory switch have landed independently. This chooser remains compatible
with both; later check-in and setup work must preserve the remote-agent
policy. That follow-up must reconcile the duplicate chooser/deletion
work and handle nonlocal capabilities without silently restoring a
local-only restriction. No changes to Riley's branches are included
here.

Generated with Goose

---------

Signed-off-by: Clay Delk <[email protected]>
Co-authored-by: Buzzsaw <a760f3ee1dc0daf403313e35766d0d983a8898aaa9ca95a034727165c63a8680@claysworld.communities.buzz.xyz>
Co-authored-by: Codex <[email protected]>
Co-authored-by: Goose <[email protected]>

Mobile Bestie used a special flat timeline that hid reply threads. It
now opens the normal DM screen, matching desktop’s pinned Bestie
(block/buzz-app#1935), with existing threads, reply actions, and
top-level sending in the same conversation.

Thread-scoped agent typing in DMs stays beneath its originating message.
Working avatars and mobile’s bouncing dots share a compact neutral
container, matching desktop’s subtle activity control. The elbow is
visible from the start, with the working container already at the final
thread-footer position. For a single-agent reply, the same avatar stays
mounted while the container and dots fade out over 200 ms, the avatar
slides into its summary position, and the reply count fades/scales in
from 95%. The elbow stays fixed. Reduced motion switches immediately.
The avatar-to-dots gap is 4 points. Reply text uses its natural line
height so its glyphs center on the avatar and elbow rather than drawing
at the top of the footer. Multi-participant summaries retain their
grouped layout. The accessible View thread action, reaction placement,
and final reply-footer position are preserved.

Validation:
- The final commit (`c6fef5d80`) passed full analysis, 4,220 Flutter
tests (40 skipped), 4 push-configuration tests, and 27 crypto tests.
- Container alignment checks pass in both directions, including avatar
continuity, intermediate fade and final geometry, reduced motion, and
thread actions. Glyph-box alignment is checked against the avatar
center. An additional regression covers a reply arriving before typing
stops and work restarting mid-transition.
- Updated DM journeys cover opening Bestie, existing threads, threaded
and top-level sending, swipe-to-reply, and absence of duplicate main-row
thread typing.
- Installed the final product source (`c6fef5d80`) in place on Pixel 10
and iPhone Air previews. The iPhone uses a release-mode preview so it
launches from the home screen; saved Kenny Lopez / Starry Night
conversation verified after install. Pixel retains Testing Agent
Sessions. The pending/midpoint/completed handoff was rendered in widget
checks, and the corrected reply-label alignment was verified on the
Pixel against the same messages before and after; human acceptance of
this final animation remains pending.
- Mandatory push hooks passed, including file-size and branch checks. A
rendered widget preview verifies the container and elbow; live
acceptance remains pending.

Self-review found no blockers in the changed paths. Review status is
preserved.

---------

Signed-off-by: kenny lopez <[email protected]>
Co-authored-by: Terp <5856f6900e8e0a4e0ea1f4f8d2ee33e4753d2119bc122f94ecafc660b46c0511@buzz.block.builderlab.xyz>

## Why

The pinned Bestie DM from block#1935 needs a clear starting point when no
Bestie is saved. The old page instead launches a separate Builderlab
setup flow. This replaces that path with one chooser for existing agents
and new agents.

## What

- Explain what a bestie means, then offer a searchable picker with
avatars, names, and distinct identity labels.
- Open the picker below its field, capped at roughly four avatar rows,
with search above scrollable results.
- Reuse **Create agent**, save the choice to the account, and open the
canonical DM.
- Keep remote agents eligible, but ask before saving: “Some bestie
features aren’t available with remote agents.” Cancel leaves the choice
unchanged and keeps any newly created agent.
- Show the chooser in place when the saved agent is gone, and clear the
account choice after completed deletion.

## How

The chooser uses `session.agentChoices`, the shared creation dialog, the
existing `main-agent` record, and the pinned DM from block#1935. It adds no
messaging path or remote capability setup. The shared Combobox gains an
opt-in compact popup; other callers keep their current behavior.

Deletion checks the current account record before writing `agent: null`.
Native signing now admits that cleared value. Existing browser journeys
retain their plugin/default and navigation contracts with the new
heading; browser cases added/removed: **0/0**. The retired hosted-setup
UI assertions are replaced by mounted chooser/save/recovery coverage.

## Risk

This removes the separate Builderlab-specific Bestie onboarding, not
Builderlab agent creation. The remote warning does not turn on memory or
check-ins. Account cleanup is a read/replace, not an atomic
compare-and-swap: another device's choice in that gap can be
overwritten. A cleanup error reports that deletion completed but the
Bestie choice could not be cleared.

## Testing

Clay tried the running native app and iterated on the empty-state copy,
searchable picker, and popup size/placement. The remote confirmation was
opened through the production chooser in an isolated Chromium fixture
with a sample hosted agent; no real agent was created or account choice
saved.

Still deferred: live Builderlab creation → confirmation → account save →
DM; deletion and reload persistence on the rebased head; native
remote-warning focus behavior; and the full light/dark, viewport, and
enlarged-text acceptance pass. These checks remain outstanding; this PR
does not claim completed acceptance.

## Bigger picture

block#1935, Riley’s Bestie tab (block#2034), and its memory switch (block#2035) are
merged. This branch includes main through `23338bc84`, preserving both
alongside the empty-state chooser.

**Overlap with Riley's block#2047:** both replace the empty Bestie page and
clear a deleted choice. This PR contains the chooser UI Clay tested
today. Riley's PR sits above the Bestie settings/memory/check-in stack,
restricts Bestie to local agents, and wires selection into that setup.
This PR deliberately allows remote agents with a warning. The tab and
memory switch have landed independently. This chooser remains compatible
with both; later check-in and setup work must preserve the remote-agent
policy. That follow-up must reconcile the duplicate chooser/deletion
work and handle nonlocal capabilities without silently restoring a
local-only restriction. No changes to Riley's branches are included
here.

Generated with Goose

---------

Signed-off-by: Clay Delk <[email protected]>
Co-authored-by: Buzzsaw <a760f3ee1dc0daf403313e35766d0d983a8898aaa9ca95a034727165c63a8680@claysworld.communities.buzz.xyz>
Co-authored-by: Codex <[email protected]>
Co-authored-by: Goose <[email protected]>