diff --git a/lsp/extensions.go b/lsp/extensions.go
index d72c3db..f06a3a0 100644
--- a/lsp/extensions.go
+++ b/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
+}
diff --git a/lsp/extensions_test.go b/lsp/extensions_test.go
index cb1007a..66e1c7b 100644
--- a/lsp/extensions_test.go
+++ b/lsp/extensions_test.go
@@ -283,3 +283,71 @@ func TestExtensionHoverWithoutProse(t *testing.T) {
 		}
 	}
 }
+
+// TestDiagnosticsExtensionOwnedARM64 pins the pass-through on arm64: the
+// lint on this base still reports a registered mnemonic as unknown, and the
+// server filters its own presentation through the registry, while a mnemonic
+// no layer registers stays reported.
+func TestDiagnosticsExtensionOwnedARM64(t *testing.T) {
+	diags := publishedDiagnostics(t, "file:///v_arm64.s", sveDoc)
+	for _, d := range diags {
+		if strings.Contains(d.Message, "SQADD") {
+			t.Errorf("registry mnemonic still reported: %+v", d)
+		}
+	}
+	unknown := 0
+	for _, d := range diags {
+		if d.Code == "unknown-instruction" {
+			unknown++
+			if !strings.Contains(d.Message, "NOSUCHTHING") {
+				t.Errorf("unknown-instruction against the wrong statement: %+v", d)
+			}
+		}
+	}
+	if unknown != 1 {
+		t.Errorf("unknown-instruction count = %d, want the one unregistered mnemonic", unknown)
+	}
+}
+
+// TestDiagnosticsExtensionOwnedFocused is the focused filter test: the
+// server's own diagnostic computation, without the protocol, answers nothing
+// against the registered mnemonics and keeps everything else.
+func TestDiagnosticsExtensionOwnedFocused(t *testing.T) {
+	srv := &Server{docs: map[string]string{"file:///v_arm64.s": sveDoc}}
+	diags := srv.diagnosticsFor("file:///v_arm64.s")
+	if len(diags) == 0 {
+		t.Fatal("diagnostics empty, want the unregistered mnemonic")
+	}
+	for _, d := range diags {
+		switch {
+		case strings.Contains(d.Message, "SQADD"):
+			t.Errorf("registry mnemonic still reported: %+v", d)
+		case d.Code == "unknown-instruction":
+			if !strings.Contains(d.Message, "NOSUCHTHING") {
+				t.Errorf("unexpected unknown-instruction: %+v", d)
+			}
+		}
+	}
+}
+
+// TestDiagnosticsExtensionAMD64StillReported is the per-architecture
+// negative case: on amd64 the registry owns nothing, so the same source
+// keeps every unknown-instruction report, the SVE mnemonics included.
+func TestDiagnosticsExtensionAMD64StillReported(t *testing.T) {
+	diags := publishedDiagnostics(t, "file:///v_amd64.s", sveDoc)
+	found := map[string]bool{}
+	for _, d := range diags {
+		if d.Code == "unknown-instruction" {
+			for _, mnem := range []string{"SQADD", "NOSUCHTHING"} {
+				if strings.Contains(d.Message, mnem) {
+					found[mnem] = true
+				}
+			}
+		}
+	}
+	for _, mnem := range []string{"SQADD", "NOSUCHTHING"} {
+		if !found[mnem] {
+			t.Errorf("amd64 lost the unknown-instruction report for %q: %+v", mnem, diags)
+		}
+	}
+}
diff --git a/lsp/handlers.go b/lsp/handlers.go
index 9017f88..66a7c4f 100644
--- a/lsp/handlers.go
+++ b/lsp/handlers.go
@@ -1127,6 +1127,13 @@ func (s *Server) diagnosticsFor(uri string) []Diagnostic {
 	cfg := lint.Config{Arch: arch.FromFilename(uriPath(uri))}
 	diags := lint.File(f, cfg)
 
+	// The extension layer owns the verdict on its own mnemonics: the registry
+	// encodes them, so a report of unknown or unencodable against a
+	// registered mnemonic is the generated table's ignorance, not the file's
+	// defect.  The filter consults the registry directly and is a no-op once
+	// lint learns the registry itself, so the two compose unchanged.
+	owned := extensionMnemonicSites(f, cfg.Arch)
+
 	out := make([]Diagnostic, 0, len(diags)+len(errs))
 	for _, e := range errs {
 		pos := token.Position{Line: 1, Column: 1}
@@ -1142,6 +1149,9 @@ func (s *Server) diagnosticsFor(uri string) []Diagnostic {
 		})
 	}
 	for _, d := range diags {
+		if extOwnedCode(d.Code) && owned[[2]int{d.Pos.Line, d.Pos.Column}] {
+			continue
+		}
 		out = append(out, Diagnostic{
 			Range:    clientRange(text, toRange(d.Pos.Line, d.Pos.Column, d.End)),
 			Severity: lintSeverity(d.Severity),