refactor(gnovm): derive IsAssignable from NameSources, drop StaticBlock.UnassignableNames

[ltzmaxwell]

Description

StaticBlock.UnassignableNames (introduced in #3198) only ever had one writer: the non-method *FuncDecl case in initStaticBlocks, which appended the func decl's name immediately after Reserve(false, nx, n, NSFuncDecl, -1) recorded the same fact in NameSources. Despite its general-sounding name, the slice never held any other kind of unassignable name — constants are const-folded (and tracked in Consts), type names fold to constTypeExpr, and uverse names are refused by an explicit branch in IsAssignable.

This PR deletes the field and answers IsAssignable from the declaring block's NameSources instead: NameSources[idx].Type != NSFuncDecl — the same idiom already used for NSTypeDecl lookups in preprocess.go. Indexing by a GetLocalIndex result is safe because Define2 enforces NumNames == len(NameSources).

Changes

• nodes.go — drop the UnassignableNames field (slot retired with a blank _ struct{} \amino:"reserved"`field, the mechanism from #5301, so field numbers are unchanged and old encoded data carrying field 8 is skipped on decode); rewriteIsAssignableto an O(1)NameSourceslookup instead of an O(n) scan, now shaped exactly like its siblingGetIsConst`.
• preprocess.go — drop the duplicate append in initStaticBlocks2.
• gnolang.proto, pb3_gen.go — regenerated with misc/genproto2 (emits reserved 8;).
• gnovm/adr/pr6089_remove_unassignable_names.md — ADR.

Verification

• go test ./gnovm/pkg/gnolang/ -short: failure set identical to pristine master on the same machine (10 pre-existing go/types wording goldens, diffed test-by-test) — nothing new.
• go test ./gno.land/pkg/sdk/vm/ -run Gas, go test ./gno.land/pkg/integration/ -run TestTestdata, go test ./tm2/pkg/amino/...: all pass.
• Decoder verified to skip reserved field 8 in old encoded data (note block nodes are not persisted to the store backend today — SetBlockNode's backend write is a TODO — so this is schema hygiene, not a live migration).

Possible follow-ups (out of scope)

• IsAssignableAt(store, path): the AssignStmt call site already has a resolved ValuePath, so the name walk could become O(depth) pointer hops, mirroring GetIsConstAt. Needs care around blank identifiers and path-refill timing.
• Merge Consts into NameSources the same way, retiring the last parallel name-list and its // TODO consider merging with Names.

Context: grew out of review discussion on #6083, where the addressability check leans on IsAssignable and the field's name suggested a completeness ("all unassignable names") it never had.

AI-assisted: implementation and ADR drafted with Claude, reviewed by the author.

🤖 Generated with Claude Code

[Gno2D2]

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