feat(compaction): conversation compacting + auto-compact threshold

Consume the compaction handoff ([email protected], [email protected]).
Re-pinned file: deps + re-mirrored .dispatch/*.reference.md.

- New 'Compaction' sidebar view (CompactionView.svelte):
  - 'Compact now' button → POST /conversations/:id/compact (loading indicator
    + result: 'N messages summarized, M kept')
  - Auto-compact threshold number input → GET/PUT
    /conversations/:id/compact-threshold (0 = disabled, default 350000)
  - Re-mounts per conversation via {#key}
- App store: compactNow() + compactThreshold reactive state +
  setCompactThreshold(), seeded on focus change (like reasoning-effort + cwd)
- conversation.compacted WS handler: reloads the SAME conversation's history
  (ID unchanged — old history forked to an archive, not a tab switch)
- WS adapter parses newConversationId field on ConversationCompactedMessage
- conformance guards + tests cover the new type

686 tests green.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/features/chat/index.ts b/src/features/chat/index.ts
index 9b94392..9c65cd4 100644
--- a/src/features/chat/index.ts
+++ b/src/features/chat/index.ts
@@ -17,6 +17,8 @@ export {
 export type { ChatStore, ChatStoreDependencies } from "./store.svelte";
 export { createChatStore } from "./store.svelte";
 export { default as ChatView } from "./ui/ChatView.svelte";
+export type { CompactNowResult, SaveCompactThresholdResult } from "./ui/CompactionView.svelte";
+export { default as CompactionView } from "./ui/CompactionView.svelte";
 export { default as Composer } from "./ui/Composer.svelte";
 export { default as ModelSelector } from "./ui/ModelSelector.svelte";
 export { default as ReasoningEffortSelector } from "./ui/ReasoningEffortSelector.svelte";