An explicitly-set empty allowlist meant 'nothing allowed' everywhere in
prose, but every boundary normalized it away:
- tui_gateway _load_enabled_toolsets converted an empty resolved set to
None (= no restriction), so platform_toolsets.cli: [] handed the
session every default toolset (#82010).
- cron create/update normalized enabled_toolsets=[] to null, and the
dispatch resolver treated a stored [] as absent (falsy), falling back
to platform_toolsets.cron.
Distinguish unset (None = no restriction, unchanged) from explicit
empty ([] = zero toolsets) end to end: the gateway returns [] bare (no
client-surface fold-in), cron persists and reloads [] verbatim, and
dispatch resolves [] to zero toolsets with no MCP merge. Absent keys
keep today's defaults.
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