egilewski found the prior sink gate was transient: it only applied while
PluginManager executed register(ctx). A plugin could defer a direct
registry.register(..., override=True) to a post-load callback/thread, after
the scope was cleared, and still replace a built-in.
Make authorization durable by binding it to where the handler is DEFINED
(handler.__globals__['__name__']) rather than to call timing. At load, each
plugin's module namespace is mapped to its allow_tool_override opt-in in a
table that is never cleared. The sink resolves the handler's owning plugin
module and rejects an override from any plugin namespace without opt-in,
regardless of when or on which thread the call happens. Plugin namespaces
with no recorded policy are treated as not-opted-in (fail-closed). Built-in
and MCP handlers live outside the plugin namespace and are unaffected.
Adds a regression test for the delayed/post-load direct-registry override.
12f5624a76