* feat(#1942): VS Code extension — repo-local IDE host with reachability proof
The VS Code extension (vscode/extension.js + vscode/package.json) is a
repo-local, buildable extension (not Marketplace-published). The gsd.invoke
handler dispatches in-process through the GSD command-routing hub. The handler
is exported separately from activate() so it is testable without a VS Code host.
tests/vscode-extension-reachability.test.cjs: proves the handler dispatches
through the hub + returns a result (keystone wired); the manifest declares the
command + engine; resolveEngineRoot finds the gsd-core/ dir.
* docs(changeset): VS Code extension (#1966)
* fix(#1942): register vscode/package.json in VERSIONED_MANIFESTS (#844)
* fix(#1942): align vscode/package.json version with package.json (1.7.0-rc.1)
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