fix: compaction keeps original ID, forks old history to archive, chains via compactedFrom

Reworked compaction to match the confirmed design:
- The compacted conversation KEEPS its original ID (messaging between
  agents is unaffected — the ID never changes)
- The old full history is forked to a new archive conversation (new UUID)
- The archive inherits the source's compactedFrom, creating a chain:
  A → Y → X (walk compactedFrom backward)
- A's history is replaced with [summary + recent N]
- A.compactedFrom = archive ID

forkHistory: inherit compactedFrom from source (not set to sourceId),
so archives chain backward to previous archives.

FE: no tab switching needed — the ID doesn't change. Just reload history.

1 files changed, 2 insertions, 2 deletions

diff --git a/packages/wire/src/index.ts b/packages/wire/src/index.ts
index 8c85f89..4ab8825 100644
--- a/packages/wire/src/index.ts
+++ b/packages/wire/src/index.ts
@@ -535,12 +535,12 @@ export interface ConversationMeta {
  * Result of a compaction operation. `summary` is the text the model produced;
  * `messagesKept` is how many recent messages were retained after the summary;
  * `messagesSummarized` is how many old messages were replaced by the summary.
- * `archiveId` is the ID of the new conversation that holds the full
+ * `newConversationId` is the ID of the new conversation that holds the full
  * pre-compaction history (non-destructive — the original history is preserved).
  */
 export interface CompactionResult {
 	readonly summary: string;
-	readonly archiveId: string;
+	readonly newConversationId: string;
 	readonly messagesSummarized: number;
 	readonly messagesKept: number;
 }