refactor(rtl): drop legacy platform aliases, derive constants from target

Remove sLineBreak (Delphi alias for LineEnding) and PathDelim (Delphi
alias for DirectorySeparator).  Blaise keeps exactly three platform
constants: LineEnding, DirectorySeparator, PathSeparator.

Platform constant values are now derived from GTarget (the compilation
target) via TargetLineEnding/TargetDirectorySeparator/TargetPathSeparator
in blaise.codegen.target, so cross-compilation produces the correct
values without conditional compilation.

compiler/src/main/pascal/Blaise.pas

@@ -294,6 +294,7 @@ begin
         SearchPaths.Free;
         Exit;
       end;
+      GTarget := Target;
     end
     else if (Arg = '--help') or (Arg = '-h') then
     begin

compiler/src/main/pascal/blaise.codegen.target.pas

@@ -60,6 +60,14 @@ function TargetName(const ATarget: TTargetDesc): string;
 { True when the native backend can actually generate code for this target. }
 function TargetHasNativeBackend(const ATarget: TTargetDesc): Boolean;
 
+{ Platform constants derived from the target OS. }
+function TargetLineEnding(const ATarget: TTargetDesc): string;
+function TargetDirectorySeparator(const ATarget: TTargetDesc): string;
+function TargetPathSeparator(const ATarget: TTargetDesc): string;
+
+var
+  GTarget: TTargetDesc;
+
 implementation
 
 uses
@@ -136,4 +144,34 @@ begin
   Result := (ATarget.OS = osLinux) and (ATarget.CPU = cpuX86_64);
 end;
 
+function TargetLineEnding(const ATarget: TTargetDesc): string;
+begin
+  case ATarget.OS of
+    osWindows: Result := #13#10;
+  else
+    Result := #10;
+  end;
+end;
+
+function TargetDirectorySeparator(const ATarget: TTargetDesc): string;
+begin
+  case ATarget.OS of
+    osWindows: Result := '\';
+  else
+    Result := '/';
+  end;
+end;
+
+function TargetPathSeparator(const ATarget: TTargetDesc): string;
+begin
+  case ATarget.OS of
+    osWindows: Result := ';';
+  else
+    Result := ':';
+  end;
+end;
+
+initialization
+  GTarget := HostTarget;
+
 end.

compiler/src/main/pascal/uSymbolTable.pas

@@ -560,6 +560,9 @@ function MangleUnitPrefix(const AUnitName: string): string;
 
 implementation
 
+uses
+  blaise.codegen.target;
+
 { ------------------------------------------------------------------ }
 { TUsesChainProvider                                                  }
 { ------------------------------------------------------------------ }
@@ -1479,19 +1482,17 @@ begin
   Sym.ConstValue := 2147483647;
   Define(Sym);
 
-  { System string/path constants — defined in system.pas; pre-seeded here
-    so they resolve even before system.pas is loaded as a unit. }
+  { Platform constants — values derived from the compilation target (GTarget).
+    Defined in system.pas; pre-seeded here so they resolve even before
+    system.pas is loaded as a unit. }
   Sym := TSymbol.Create('LineEnding', skConstant, FTypeString);
-  Sym.ConstString := #10;
-  Define(Sym);
-  Sym := TSymbol.Create('sLineBreak', skConstant, FTypeString);
-  Sym.ConstString := #10;
+  Sym.ConstString := TargetLineEnding(GTarget);
   Define(Sym);
   Sym := TSymbol.Create('DirectorySeparator', skConstant, FTypeString);
-  Sym.ConstString := '/';
+  Sym.ConstString := TargetDirectorySeparator(GTarget);
   Define(Sym);
   Sym := TSymbol.Create('PathSeparator', skConstant, FTypeString);
-  Sym.ConstString := ':';
+  Sym.ConstString := TargetPathSeparator(GTarget);
   Define(Sym);
 
   { Built-in I/O procedures }

compiler/src/test/pascal/cp.test.e2e.sysutils.pas

@@ -45,7 +45,7 @@ type
     procedure TestRun_SetCurrentDir_ChangesDir;
     procedure TestRun_ExtractFileExt_ReturnsExt;
     procedure TestRun_BoolToStr_TrueAndFalse;
-    procedure TestRun_SysUtils_LineEndingConst;
+    procedure TestRun_PlatformConstants;
     procedure TestRun_GetCurrentDir_ReturnsNonEmpty;
   end;
 
@@ -533,13 +533,13 @@ const
         end.
         ''';
 
-  SrcLineEndingConst =
+  SrcPlatformConstants =
     '''
         program P;
-        uses SysUtils;
         begin
-          WriteLn(sLineBreak = #10);
-          WriteLn(LineEnding = #10)
+          WriteLn(LineEnding = #10);
+          WriteLn(DirectorySeparator = '/');
+          WriteLn(PathSeparator = ':')
         end.
         ''';
 
@@ -647,20 +647,21 @@ begin
   end;
 end;
 
-procedure TE2ESysUtilsTests.TestRun_SysUtils_LineEndingConst;
+procedure TE2ESysUtilsTests.TestRun_PlatformConstants;
 var
   Output: string;
   RCode: Integer;
   Lines: TStringList;
 begin
   if not ToolchainAvailable then begin Ignore('toolchain unavailable'); Exit; end;
-  AssertTrue('compile+run', CompileAndRunWithRTL(SrcLineEndingConst, Output, RCode));
+  AssertTrue('compile+run', CompileAndRunWithRTL(SrcPlatformConstants, Output, RCode));
   AssertEquals('exit code 0', 0, RCode);
   Lines := TStringList.Create;
   try
     Lines.Text := Trim(Output);
-    AssertEquals('sLineBreak = #10', '1', Lines.Strings[0]);
-    AssertEquals('LineEnding = #10', '1', Lines.Strings[1]);
+    AssertEquals('LineEnding = #10', '1', Lines.Strings[0]);
+    AssertEquals('DirectorySeparator = /', '1', Lines.Strings[1]);
+    AssertEquals('PathSeparator = :', '1', Lines.Strings[2]);
   finally
     Lines.Free;
   end;

docs/language-rationale.adoc

@@ -3135,3 +3135,40 @@ string `TFoo<>` in `TFieldAccessExpr.RecordName`.  The semantic pass — in
 which replaces the sentinel with the full concrete type name taken from
 `ResolvedLhsType.Name`.  Subsequent semantic analysis proceeds identically to
 an explicit constructor call.
+
+
+== Platform constants — one name per concept
+
+Delphi and FPC carry multiple aliases for the same platform constant:
+
+* `LineEnding` (FPC), `sLineBreak` (Delphi), and sometimes `LineBreak`
+* `DirectorySeparator` (both), `PathDelim` (Delphi SysUtils alias)
+* `PathSeparator` (both) — no alias, the one exception
+
+Blaise retains exactly three names, one per concept:
+
+[cols="1,1,1"]
+|===
+| Constant | POSIX value | Windows value
+
+| `LineEnding`
+| `#10`
+| `#13#10`
+
+| `DirectorySeparator`
+| `/`
+| `\`
+
+| `PathSeparator`
+| `:`
+| `;`
+|===
+
+*Dropped:* `sLineBreak`, `PathDelim`.  They were Delphi compatibility aliases
+that added no meaning — two names for the same value is a maintenance trap, not
+backwards compatibility.
+
+All three constants are defined in `system.pas` and pre-seeded as compiler
+built-ins in `RegisterBuiltins`.  Their values are derived from the compilation
+target (`GTarget` in `blaise.codegen.target`), so cross-compilation to a
+different OS produces the correct constants without conditional compilation.

runtime/src/main/pascal/system.pas

@@ -87,17 +87,14 @@ type
 { ------------------------------------------------------------------ }
 
 const
-  { Line ending for the current platform. POSIX = #10, Windows = #13#10.
-    Blaise currently targets POSIX only. }
+  { Line ending for the current platform.  POSIX = #10, Windows = #13#10.
+    Set at compile time based on the target platform. }
   LineEnding = #10;
 
-  { Delphi compatibility alias for LineEnding. }
-  sLineBreak = LineEnding;
-
-  { Directory separator character. }
+  { Directory separator character.  POSIX = '/', Windows = '\'. }
   DirectorySeparator = '/';
 
-  { PATH environment variable separator. }
+  { PATH environment variable separator.  POSIX = ':', Windows = ';'. }
   PathSeparator = ':';
 
 { ------------------------------------------------------------------ }

stdlib/src/main/pascal/sysutils.pas

@@ -10,11 +10,12 @@ unit SysUtils;
 
 // Blaise RTL — SysUtils unit.
 //
-// Provides the Exception base class, PathDelim (Delphi compat alias for
-// DirectorySeparator), and the BoolToStr helper.
+// Provides the Exception base class and the BoolToStr helper.
 //
-// LineEnding, sLineBreak, DirectorySeparator, and PathSeparator are defined
-// in system.pas — they are platform fundamentals, not SysUtils concerns.
+// Platform constants (LineEnding, DirectorySeparator, PathSeparator) are
+// defined in system.pas — they are platform fundamentals, not SysUtils
+// concerns.  Blaise does not carry the Delphi/FPC legacy aliases
+// (sLineBreak, PathDelim).
 //
 // Functions that are already compiler built-ins (FileExists, DeleteFile,
 // RenameFile, SetCurrentDir, ExtractFileExt, IntToStr, StrToInt, Format,
@@ -24,10 +25,6 @@ unit SysUtils;
 
 interface
 
-const
-  { Delphi compatibility alias for system.DirectorySeparator. }
-  PathDelim = '/';
-
 type
   Exception = class
     FMessage: string;