feat(lsp): leave the extension verdicts to the registry

Diagnostics no longer repeat the generated table's ignorance of a
registered mnemonic: unknown-instruction and unencodable-instruction
against a statement the registry encodes are filtered from the server's
own presentation, driven by asm.LookupExtension directly.  The filter is
a no-op once lint learns the registry, so the two compose unchanged.

Assisted-by: GLM 5.3 Flash

lsp/extensions.go

@@ -21,6 +21,8 @@ import (
 
 	"sourcedock.dev/petrbalvin/gasm-sdk/arch"
 	"sourcedock.dev/petrbalvin/gasm-sdk/asm"
+	"sourcedock.dev/petrbalvin/gasm-sdk/ast"
+	"sourcedock.dev/petrbalvin/gasm-sdk/lint"
 )
 
 // extFormDoc is the rendering of one registered form: everything hover and
@@ -346,3 +348,39 @@ func applyExtensionCompletion(items []CompletionItem, a arch.Arch) []CompletionI
 	}
 	return items
 }
+
+// extOwnedCode reports whether a lint code carries a verdict the extension
+// layer owns: the two that accuse a mnemonic of not existing or of not being
+// encodable.  The operand-count rule stays with the generated table, whose
+// bounds the relaxed architectures never fire against a registered form.
+func extOwnedCode(code string) bool {
+	return code == lint.CodeUnknownInstr || code == lint.CodeUnencodable
+}
+
+// extensionMnemonicSites collects the source positions of the statements
+// whose mnemonic the architecture's extension layer registers.  The
+// diagnostics pass consults it to leave the layer's verdicts to the layer:
+// a registry mnemonic is neither unknown nor unencodable, the registry
+// encodes it.
+func extensionMnemonicSites(f *ast.File, a arch.Arch) map[[2]int]bool {
+	out := make(map[[2]int]bool)
+	if f == nil {
+		return out
+	}
+	for _, d := range f.Decls {
+		t, ok := d.(*ast.Text)
+		if !ok {
+			continue
+		}
+		for _, s := range t.Body {
+			in, ok := s.(*ast.Instr)
+			if !ok {
+				continue
+			}
+			if _, ok := asm.LookupExtension(a, in.Mnemonic.Text); ok {
+				out[[2]int{in.Mnemonic.Pos.Line, in.Mnemonic.Pos.Column}] = true
+			}
+		}
+	}
+	return out
+}