fix(#471): SET format = json now takes effect for subsequent statements

execSet stored the format value in ctx.Settings but never applied it to
ctx.Format, and syncBack intentionally excluded Format from being written
back to e.format — so the output format never changed.

Fix: execSet applies the 'format' key to ctx.Format immediately; syncBack
now persists e.format = ctx.Format so subsequent statements in the same
session inherit the new setting.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ako

mdl/executor/cmd_misc.go

@@ -43,6 +43,17 @@ func execSet(ctx *ExecContext, s *ast.SetStmt) error {
 		ctx.Settings = make(map[string]any)
 	}
 	ctx.Settings[s.Key] = s.Value
+
+	// Apply recognized session keys to the live context immediately.
+	// syncBack will persist ctx.Format back to e.format so subsequent
+	// statements in the same session also pick up the change.
+	switch strings.ToLower(s.Key) {
+	case "format":
+		if v, ok := s.Value.(string); ok {
+			ctx.Format = OutputFormat(strings.ToLower(v))
+		}
+	}
+
 	fmt.Fprintf(ctx.Output, "Set %s = %v\n", s.Key, s.Value)
 	return nil
 }

mdl/executor/cmd_misc_mock_test.go

@@ -72,6 +72,39 @@ func TestHelp_Mock(t *testing.T) {
 	assertContainsStr(t, out, "connect local")
 }
 
+// ---------------------------------------------------------------------------
+// SET — format key updates ctx.Format
+// ---------------------------------------------------------------------------
+
+func TestExecSet_FormatKey_UpdatesCtxFormat(t *testing.T) {
+	ctx, buf := newMockCtx(t) // starts as FormatTable (default)
+	if ctx.Format != FormatTable {
+		t.Fatalf("expected default FormatTable, got %q", ctx.Format)
+	}
+	err := execSet(ctx, &ast.SetStmt{Key: "format", Value: "json"})
+	assertNoError(t, err)
+	if ctx.Format != FormatJSON {
+		t.Errorf("expected ctx.Format = %q after SET format=json, got %q", FormatJSON, ctx.Format)
+	}
+	assertContainsStr(t, buf.String(), "Set format = json")
+}
+
+func TestExecSet_FormatKey_BareIdentifier(t *testing.T) {
+	ctx, _ := newMockCtx(t)
+	assertNoError(t, execSet(ctx, &ast.SetStmt{Key: "format", Value: "table"}))
+	if ctx.Format != FormatTable {
+		t.Errorf("expected FormatTable, got %q", ctx.Format)
+	}
+}
+
+func TestExecSet_UnknownKey_StoredOnly(t *testing.T) {
+	ctx, _ := newMockCtx(t)
+	assertNoError(t, execSet(ctx, &ast.SetStmt{Key: "mykey", Value: "myval"}))
+	if ctx.Settings["mykey"] != "myval" {
+		t.Errorf("expected Settings[mykey]=myval, got %v", ctx.Settings["mykey"])
+	}
+}
+
 // ---------------------------------------------------------------------------
 // EXECUTE SCRIPT — depth limit
 // ---------------------------------------------------------------------------

mdl/executor/executor_dispatch.go

@@ -29,14 +29,18 @@ func (e *Executor) executeInner(ctx context.Context, stmt ast.Statement) error {
 // the next newExecContext call picks up handler-side state changes.
 //
 // Fields intentionally NOT synced back (read-only from handler perspective):
-//   - Output, Format, Quiet, Logger — set once at Executor construction
+//   - Output, Quiet, Logger — set once at Executor construction
 //   - BackendFactory — set once at Executor construction
 //   - OutputGuard — removed; writeDescribeJSON captures via Output swap only
 //   - ExecuteFn, ExecuteProgramFn, FinalizeFn — bound to Executor methods, immutable
+//
+// Format IS synced back so that `SET format = json` takes effect for all
+// subsequent statements in the same session.
 func (e *Executor) syncBack(ctx *ExecContext) {
 	e.backend = ctx.Backend
 	e.mprPath = ctx.MprPath
 	e.cache = ctx.Cache
+	e.format = ctx.Format
 	e.catalogMu.Lock()
 	old := e.catalog
 	e.catalog = ctx.Catalog