feat: conversation compacting (manual + automatic)

Implement roadmap item 10: conversation compaction to reclaim context
window without losing the thread.

Wire (0.11.0):
- Add CompactionResult type
- Add ConversationCompactedMessage WS event

Transport-contract (0.15.0):
- Add CompactResponse, CompactThresholdResponse, SetCompactThresholdRequest
- Add ConversationCompactedMessage to WsServerMessage union
- Re-export CompactionResult

Conversation-store:
- replaceHistory: delete all chunks, reset seq, append new messages
- getCompactThreshold / setCompactThreshold (per-conversation setting)
- compactThresholdKey added to keys.ts

Session-orchestrator:
- CompactionService interface + compactionHandle
- conversationCompacted hook descriptor
- createCompactionService: load history, split old/recent, call provider
  to summarize, replaceHistory with [system: summary] + recent N
- Auto-trigger: resolveCompaction lazy dep, fires after turn settles
  (checks threshold, non-blocking)
- Hook declared in manifest contributes.hooks + services

Transport-http:
- POST /conversations/:id/compact (manual trigger)
- GET /conversations/:id/compact-threshold (read setting)
- PUT /conversations/:id/compact-threshold (set setting)

Transport-ws:
- Subscribe to conversationCompacted hook
- Broadcast conversation.compacted WS message

CLI:
- dispatch compact <conversationId> command

FE handoff: frontend-compaction-handoff.md

1 files changed, 23 insertions, 0 deletions

diff --git a/packages/cli/src/args.ts b/packages/cli/src/args.ts
index 30fa309..ecf6e2e 100644
--- a/packages/cli/src/args.ts
+++ b/packages/cli/src/args.ts
@@ -34,6 +34,7 @@ export type ParsedCommand =
 			readonly status?: string;
 			readonly all: boolean;
 	  }
+	| { readonly kind: "compact"; readonly server: string; readonly conversationId: string }
 	| { readonly kind: "open"; readonly server: string; readonly conversationId: string }
 	| { readonly kind: "read"; readonly server: string; readonly conversationId: string }
 	| {
@@ -108,6 +109,28 @@ export function parseArgs(argv: readonly string[], opts: ParseOpts): ParsedComma
 		};
 	}
 
+	if (first === "compact") {
+		let server = opts.defaultServer;
+		let conversationId: string | undefined;
+		for (let i = 1; i < argv.length; i++) {
+			const arg = argv[i] as string;
+			if (arg === "--server") {
+				if (i + 1 >= argv.length) return { kind: "error", message: "--server requires a value" };
+				server = argv[++i] as string;
+			} else if (arg.startsWith("--")) {
+				return { kind: "error", message: `Unknown flag: ${arg}` };
+			} else if (conversationId !== undefined) {
+				return { kind: "error", message: `Unexpected argument for 'compact': ${arg}` };
+			} else {
+				conversationId = arg;
+			}
+		}
+		if (conversationId === undefined) {
+			return { kind: "error", message: "'compact' requires a conversation id" };
+		}
+		return { kind: "compact", server, conversationId };
+	}
+
 	if (first === "read") {
 		let server = opts.defaultServer;
 		let conversationId: string | undefined;