feat(chat): make v0.0.1 standalone with Cave optional

[BunsDev]

Why

The app blocked every user behind a Cave connection gate. A first public
release could not be opened at all without a paired Cave instance, which
contradicts shipping v0.0.1 as a standalone product.

Cave Client v1 also exposes no write operation — CAVE_OPERATIONS in
@opencoven/sdk-core lists 13 ops and none of them create a message. So no
amount of gate tuning would have made the app writable; reads and writes had to
become separate ports.

Design approved in docs/standalone-query-adapter-design.md (commit 2ed75f9).

What changed

New local layer (src/lib/local/)

File	Role
chat-records.ts	Record shapes + the ChatBackend port. commit() takes whole records so a message append and its conversation's updatedAt bump land atomically.
indexeddb-backend.ts	Durable backend. Both object stores written in one readwrite transaction.
memory-backend.ts	Fallback reporting isDurable() === false.
chat-store.ts	In-memory index, keyset cursors, subscriptions.
local-query-adapter.ts	The existing QueryAdapter interface over local storage.
chat-writer.ts	WriteResult with 'unsupported' as a first-class outcome.
chat-source.ts	Pairs an adapter with a writer.

Wiring

• src/app.tsx — local source mounts immediately; Cave connects only after the
  user clicks Connect to Cave. The installation-ID gate now disables Cave
  pairing only (it feeds pairingIdentity and nothing else). A dropped Cave
  connection falls back to local rather than showing an empty view.
• src/chat-shell.tsx — exactly two new optional props (revision, writer)
  plus a composer. The read path is unchanged.
• src/chat-composer.tsx / .css — the composer.

Decisions worth reviewing

Keyset cursors, not offset. createManualPageWalk aborts a walk the moment
a cursor value repeats, and offset cursors repeat as soon as a row is inserted
mid-walk. Cursors therefore name the last row served ({v,t,i}, base64url).

The local adapter reimplements QueryAdapter rather than wrapping
createQueryAdapter. Every reason that adapter exists — network latency,
request dedup, abort handling, TTL caching over a socket — is absent here. Reads
are synchronous map lookups; a cache in front of them would only add a window in
which the UI shows data the store has already replaced.

No assistant reply is fabricated. There is no model backend in this release.
The composer states that no reply will arrive rather than inventing canned text.

The memory fallback is never silent. When IndexedDB is unavailable the
composer says the messages are kept in memory only and will be lost.

APP_PHASE deliberately unchanged. It mirrors a value in
src-tauri/src/metadata.rs that the conformance lock pins, so it moves only
alongside a Rust change and a repin. Flagged for a follow-up, not smuggled in
here.

Verification

• corepack pnpm typecheck — clean
• corepack pnpm lint — clean except the 7 pre-existing noDescendingSpecificity
  warnings in src/demo/chat-demo.css (owned by the warnings lane)
• corepack pnpm vitest run — 409 passed, 61 skipped, 0 failed
• corepack pnpm build — succeeds
• Real Chromium run against the built bundle: created a conversation, sent a
  message, reloaded the page and the message survived via IndexedDB, with
  zero console errors and the Cave source correctly disabled.

27 new tests cover cursor round-tripping, a full page walk driven through the
real createManualPageWalk, cursor-echo and no-repeat guarantees, commit
atomicity, rollback on backend failure, corrupt-row sanitizing, orphan-message
dropping, validation codes, and a shared adapter-contract suite. src/app.test.tsx
was rewritten for the opt-in Cave flow; the three e2e specs were updated to match.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[Copilot]

Pull request overview

This PR makes the Chat app usable as a standalone product by introducing a local storage-backed chat source (IndexedDB with in-memory fallback) and making Cave pairing optional/opt-in, while keeping the existing read-path QueryAdapter contract intact.

Changes:

• Added a local chat persistence layer (ChatStore + backends) and a local QueryAdapter implementation.
• Split read/write concerns via a ChatWriter so local is writable while Cave remains read-only.
• Updated app and shell wiring/UI to mount local immediately, add a composer + “New conversation”, and gate Cave behind an explicit “Connect to Cave” flow (tests updated accordingly).

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/lib/local/chat-records.ts	Defines local record shapes, backend port, and sanitization utilities.
src/lib/local/indexeddb-backend.ts	Implements durable IndexedDB backend for local records.
src/lib/local/memory-backend.ts	Adds non-durable in-memory backend fallback when IndexedDB is unavailable.
src/lib/local/chat-store.ts	In-memory index + keyset pagination + atomic commit semantics over a backend.
src/lib/local/local-query-adapter.ts	Implements existing QueryAdapter interface over the local store.
src/lib/local/chat-writer.ts	Introduces a write port with explicit unsupported outcomes for Cave.
src/lib/local/chat-source.ts	Packages adapter + writer into switchable sources (local vs cave).
src/lib/local/local-chat.test.ts	Adds comprehensive unit coverage for local cursors, paging, writes, adapter contract, and fallback.
src/lib/app-metadata.ts	Updates app metadata strings to reflect standalone/local-first positioning.
src/chat-shell.tsx	Adds optional writer/revision props, composer rendering, and “New” conversation button.
src/chat-composer.tsx	New message composer for local writes with durability disclosure and error display.
src/chat-composer.css	Styling for source bar, Cave connect surface, composer, and “New conversation” button.
src/app.tsx	Rewires startup: local mounts immediately; Cave becomes opt-in and source-switchable.
src/app.test.tsx	Updates app tests for opt-in Cave, local-first behavior, and composer behavior.
e2e/connection-gate.spec.ts	Adjusts browser expectations to local-first and composer behavior without Cave.
e2e/app.tauri-mock.spec.ts	Updates mocked Tauri e2e flow to opt in to Cave before asserting Cave UI.
e2e/app.spec.ts	Updates baseline e2e test to assert shell mounts without a blocking gate.
docs/standalone-query-adapter-design.md	Adds design doc describing the standalone/local-first approach and constraints.

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