Update the Core compile options and Server replacement values to the current LayerNode API. Preserve test expectations, replacement targets, and layer lifetimes.
Replace exposed layer graph assembly with opaque declarations, checked substitutions, and lifetime-aware compilation. Preserve deep replacement, ordered startup, and Effect-owned resource lifetimes; migrate callers and verify source and published package contracts.
Keep the title and workspace label above scrollable sidebar details. Disable the unused horizontal scrollbar and place the automatic vertical scrollbar in the reserved gutter so tab changes do not flash or shift the sidebar.
Configure custom Markdown renderers before assigning content and share a reactive message-position index across assistant footers. Preserve completion ordering and historical footer metrics, with regression coverage for prepend, same-length refresh, and revert.