One deb block per package cannot express two series needing different
rules. Make pull and deb lists of entries, each with its own series
scope: every matching entry applies, in file order, so a stonking
entry can carry its own dependency rules next to the resolute one.
Thread the series through find_package_directory for the
package_directory lookup, which keeps its deb-then-pull fallback.
The resolute linux and linux-riscv controls declare llvm-21-dev
unqualified while their other llvm pieces are :native, so the dpkg
cross rules resolve it against the host architecture — whose
dependency closure needs python3:riscv64, conflicting with the
python3 the control itself declares :native. No resolver can install
that set; sbuild fails on it identically.
Give the deb quirks a dependencies rule set rather than a one-off
native-qualification knob: replace rewrites a declared dependency by
name with a full dependency string (qualifier, version and
restrictions included), inject adds dependencies resolved as if
declared, drop ignores declared ones. Entries are scoped by series so
they can be dropped when the upstream packaging catches up, and rule
names that match nothing are warned about so stale quirks surface.
Ship the llvm-21-dev entry for the resolute kernels: resolve it as
llvm-21-dev:native, keeping the declared <!stage1> restriction.