FIX + feat: add MessageManager layer for centralized history coordination #19653

Job	Run time
check-translations	41s
knip	53s
compile	2m 21s
platform-unit-test (windows-latest)	8m 20s
check-openrouter-api-key	4s
platform-unit-test (ubuntu-latest)	4m 43s
integration-test	3m 14s
	20m 16s

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