Moved the cross-spawn-spawner module from packages/opencode to packages/core
to enable code sharing across the monorepo. This consolidates the process
spawning infrastructure into the core package so other packages can use
cross-platform child process spawning without duplicating the implementation.
Updated all import statements across the codebase to reference the new
location (@opencode-ai/core/effect/cross-spawn-spawner). Removed the
local copy from the opencode package along with its tests.
Moves effect logging, observability, runtime utilities, flags, installation
version info, and process utilities from opencode to core package. This
enables better code sharing across packages and establishes core as the
single source of truth for foundational utilities.
All internal imports updated to use @opencode-ai/core paths for consistency.
