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/adapters/ws/logic.ts b/src/adapters/ws/logic.ts
index 53955f8..b11c5c4 100644
--- a/src/adapters/ws/logic.ts
+++ b/src/adapters/ws/logic.ts
@@ -136,11 +136,13 @@ export function parseServerMessage(data: string): WsServerMessage | null {
 		}
 		case "conversation.compacted": {
 			if (typeof parsed.conversationId !== "string") return null;
+			if (typeof parsed.newConversationId !== "string") return null;
 			if (typeof parsed.messagesSummarized !== "number") return null;
 			if (typeof parsed.messagesKept !== "number") return null;
 			const msg: ConversationCompactedMessage = {
 				type: "conversation.compacted",
 				conversationId: parsed.conversationId,
+				newConversationId: parsed.newConversationId,
 				messagesSummarized: parsed.messagesSummarized,
 				messagesKept: parsed.messagesKept,
 			};