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>

_FiveSql2/src/TFiveSQL.prg

@@ -24,7 +24,16 @@
  * during Run() never corrupt the cached tree.
  *
  * Cached entries live until process exit; distinct SQL text count is
- * bounded by the caller's template set, so LRU is deferred. */
+ * bounded by the caller's template set in well-behaved callers, but
+ * a long-running server with diverse dynamic SQL (or one that bypasses
+ * the `?` placeholder convention and bakes literals into every query)
+ * can grow this hash without bound. SQL_PLAN_CACHE_MAX caps the entry
+ * count; on overflow we wipe the whole cache. Coarser than LRU but
+ * Five hashes have no insertion-order guarantee and the per-query
+ * bookkeeping for true LRU would dominate the parse cost we're
+ * trying to amortise. Reset cost is one extra parse per template
+ * already evicted, accepted in exchange for bounded memory. */
+#define SQL_PLAN_CACHE_MAX 1000
 STATIC s_hPlanCache := { => }
 
 CLASS TFiveSQL
@@ -53,7 +62,14 @@ RETURN SELF
 METHOD Execute( cSQL, bBlock ) CLASS TFiveSQL
 
    LOCAL aTokens, hQuery, aResult
-   LOCAL aLex, cKey, aParams
+   LOCAL aLex, cKey, aParams, cVerPrefix
+
+   /* Schema-version prefix: DDL (CREATE/ALTER/DROP) bumps SqlSchemaVer()
+    * so any plan that resolved columns or indexes against the pre-DDL
+    * schema misses the cache on the next call and gets re-parsed /
+    * re-compiled against the current layout. The prefix also flows
+    * through to s_hDmlPcodeCache via ::oExec:cCacheKey below. */
+   cVerPrefix := hb_NToS( SqlSchemaVer() ) + "|"
 
    /* Fast path: no explicit aParams → single Go RTL lex+normalize call
     * (SqlLexAndExtractTemplate). Returns {aTokens, cKey, aParams}; the
@@ -63,7 +79,7 @@ METHOD Execute( cSQL, bBlock ) CLASS TFiveSQL
    IF Empty( ::aParams )
       aLex := SqlLexAndExtractTemplate( cSQL )
       aTokens := aLex[ 1 ]
-      cKey := aLex[ 2 ]
+      cKey := cVerPrefix + aLex[ 2 ]
       aParams := aLex[ 3 ]
 
       IF hb_HHasKey( s_hPlanCache, cKey )
@@ -74,6 +90,10 @@ METHOD Execute( cSQL, bBlock ) CLASS TFiveSQL
          IF hQuery == NIL
             RETURN { { "__error__" }, { { SQL_ERR_SYNTAX, "Failed to parse SQL", cSQL } } }
          ENDIF
+         IF Len( s_hPlanCache ) >= SQL_PLAN_CACHE_MAX
+            s_hPlanCache := { => }
+            SqlDmlPcodeCacheReset()
+         ENDIF
          s_hPlanCache[ cKey ] := HbDeepClone( hQuery )
       ENDIF
 
@@ -81,8 +101,9 @@ METHOD Execute( cSQL, bBlock ) CLASS TFiveSQL
       ::oExec:cCacheKey := cKey
    ELSE
       /* Caller supplied explicit params — cache by raw SQL text. */
-      IF hb_HHasKey( s_hPlanCache, cSQL )
-         hQuery := HbDeepClone( s_hPlanCache[ cSQL ] )
+      cKey := cVerPrefix + cSQL
+      IF hb_HHasKey( s_hPlanCache, cKey )
+         hQuery := HbDeepClone( s_hPlanCache[ cKey ] )
       ELSE
          aTokens := SqlLexerTokenize( cSQL )
          ::oParser := TSqlParser2():New( aTokens, ::aParams )
@@ -90,11 +111,15 @@ METHOD Execute( cSQL, bBlock ) CLASS TFiveSQL
          IF hQuery == NIL
             RETURN { { "__error__" }, { { SQL_ERR_SYNTAX, "Failed to parse SQL", cSQL } } }
          ENDIF
-         s_hPlanCache[ cSQL ] := HbDeepClone( hQuery )
+         IF Len( s_hPlanCache ) >= SQL_PLAN_CACHE_MAX
+            s_hPlanCache := { => }
+            SqlDmlPcodeCacheReset()
+         ENDIF
+         s_hPlanCache[ cKey ] := HbDeepClone( hQuery )
       ENDIF
 
       ::oExec := TSqlExecutor():New( hQuery, ::aParams )
-      ::oExec:cCacheKey := cSQL
+      ::oExec:cCacheKey := cKey
    ENDIF
 
    ::oExec:bRowBlock := bBlock