Without rollback, a brief that fails (network error, abort signal, parse
error, etc) before any sub-agent content lands permanently mutates the
user's doc.variables with the plan's palette — they see no design, but
their token state is now polluted with whatever style guide the planner
picked. Next brief on the same doc inherits this stale palette.
Fix: snapshot the 7 plan-derived variable names BEFORE seedDocVariables-
FromStyleGuide writes them, and in the existing catch block restore the
snapshot iff no content survived (every root frame got cleaned up). With
partial content surviving (a salvageable half-design) we keep the seeded
palette so existing $color-* refs in those nodes still resolve correctly.
design.md flows still bypass this entirely; user-set variables outside
the plan-derived 7 are untouched on both seed and rollback.
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