checkpoint: season-wide bug fix campaign + infra

Cumulative season's silent-bug hunting (~62 fixes) across the FiveSql2
SQL engine, the Five compiler/runtime, and the hbrdd RDD layer. Saved
as a single checkpoint before refactoring the parser to delegate xBase
command translation to the preprocessor.

Highlights:

FiveSql2 engine (_FiveSql2/src/)
- prefix-glob index attach -> explicit convention (<table>_pk.ntx,
  <table>_uq.ntx, <table>.cdx) — fixes silent multi-row INSERT row-drop
- DROP/CREATE TABLE FErase chain extended (.cdx, .fsc, .fsv, .dbt, .fpt)
- COUNT(DISTINCT col) parsed + aggregated via hSeen hash
- UNION column-count mismatch returns SQL_ERR_GRAMMAR (was silent)
- DISTINCT + ORDER BY hidden-col leak fixed (trim before DISTINCT)
- Derived table FROM (SELECT...) + JOIN right-side derived
- Self-FK CASCADE depth 2+ via SqlGetSingleColPK pre-collect
- LAG/LEAD default arg uses SqlEvalRowExpr (handles -N const exprs)
- DATE literal round-trip validation (Feb 29 non-leap rejected)
- CREATE OR REPLACE VIEW; CREATE VIEW errors on already-exists
- AlterTable type dispatcher comma-wrapped (1-char type "A" no longer
  matches CHARACTER)

Compiler / runtime
- gengo: HB_ -> FV_ prefix on emitted Go function names (Five identity)
- gengo split: emit_block.go, emit_stmt.go, folding.go extracted
- parser/stmtreg.go nudges
- hbrt: debug TUI/CLI restructure (debugcmd, debugkey, termios_*),
  windows debug stubs collapsed
- thread/vm/value/class/pcinterp tightening from panic traces

RDD layer (hbrdd/)
- dbf: null bitmap support (null.go + null_test.go), mmap split
  (mmap_posix.go / mmap_windows.go), byte-level numeric parse
- ntx/cdx: windows mmap parity
- workarea + mem RDD: cross-area state-bleed fixes

RTL (hbrtl/)
- errorlog rewrite with platform-specific FD (errorlog_fd_unix /
  errorlog_fd_other)
- sqlscan, sqlhelpers, indexrtl, datetime extensions

Gates green at checkpoint:
- go test ./...        : PASS
- FiveSql2 SQL:1999    : 43/43
- Harbour compat       : 56/56

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

compiler/parser/parser.go

@@ -1832,7 +1832,32 @@ func (p *Parser) parseUse() *ast.UseCmd {
 
 func (p *Parser) parseSelect() *ast.SelectCmd {
 	pos := p.expect(token.SELECT).Pos
-	area := p.parseExpr()
+	// Classic Clipper/Harbour semantics: `SELECT <alias>` treats a bare
+	// identifier as a literal alias name (string), not as an expression.
+	// Wrap in parens to force expression evaluation — e.g. `SELECT (n)`
+	// where n is a local holding an area number or alias name.
+	//
+	// Without this, unresolved identifiers fell back to PushMemvar(name)
+	// which returned NIL, and _wa.Select("") quietly allocated a fresh
+	// empty workarea, stranding the caller's real data in the previous
+	// slot. Visible symptom: `SELECT ALTSRC` inside SqlAlterAddColumn
+	// picked up a phantom area and the row-copy loop saw EOF from the
+	// first iteration (no rows migrated).
+	var area ast.Expr
+	if p.current.Kind == token.IDENT {
+		// Peek: only treat bare IDENT as literal alias when it's the
+		// entire argument (next token ends the statement). `SELECT x:y`
+		// or `SELECT f()` must parse as expressions so the dispatch
+		// below still routes through parseExpr.
+		next := p.peekAt(1)
+		if next == token.NEWLINE || next == token.SEMICOLON || next == token.EOF {
+			tok := p.advance()
+			area = &ast.LiteralExpr{ValuePos: tok.Pos, Kind: token.STRING, Value: tok.Literal}
+		}
+	}
+	if area == nil {
+		area = p.parseExpr()
+	}
 	p.expectEndOfStmt()
 	return &ast.SelectCmd{SelectPos: pos, Area: area}
 }