fix(agent): filter SDK metadata from messages/partial events #328

Job	Run time
Chat Agent — smoke	1m 23s
Library — lint / test / build	1m 9s
Cockpit — representative capability smoke	1m 10s
Cockpit — build all examples	4m 53s
Cockpit — e2e	1m 59s
Website — lint / build	1m 42s
Website — e2e	2m 22s
Cockpit — secret-gated integration	1m 9s
Cockpit — build / test	1m 34s
Cockpit — deploy smoke dry-run	1m 8s
Deploy → Vercel	0s
Production smoke	-1s
	18m 28s

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