wwstage's checker rejected matching an imported union's variants cross-module: casevariantin/casecovers' typeeqast did a raw streq, so a union's bare variant "unsupported" failed to match the dotted case pattern "errors.unsupported" (cstage compares resolved-Type identity, qualifier-agnostic). Add a (module, leaf)-pair fallback after typeeqast: reduce both the case pattern and each variant to (module, leaf) and match on pair equality -- a dotted name keeps its own qualifier, a bare name takes the union's defining module (taggeddefmod, via the aliassym hop chain). This closes BOTH directions: the false-reject of valid cross-module match AND a false-accept of a foreign same-leaf qualifier (case othermod.foo vs errors.error now rejected, matching cstage). Handles the nested errors.error-in-io.error case (the dotted variant keeps mod=errors, not the union's mod=io). typeeqast stays the first check so currently-valid code is byte-id-unchanged; the pair-match fires only on the previously-rejected qualified-vs-bare mix. Wired into casevariantin, casecovers, and the is/as caller. Adds test/wcc/787 (cross-module positive, exhaustiveness, foreign-qualifier reject-guard, dotted-variant body). Unblocks #5's cross-module io.error/errors.error decomposition. rule-10 fix-up; #10-family (wwstage cross-module resolution).
Hojun-Cho
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