feat(kanban): detect and merge external file changes in TUI

Add file-change monitoring to the kanban TUI so that tasks added via CLI
(or any external process) while the TUI is running are automatically
merged into the live view instead of being silently overwritten on save.

The implementation has three layers:

1. New FileAge built-in (compiler + runtime): returns the file's mtime as
   Int64 via stat(), or -1 if the file does not exist.  Follows the same
   pattern as FileExists — symbol table registration, semantic analysis,
   codegen, and POSIX ABI stub.

2. Merge-aware TBoard (kanban.data): tracks last-known mtime, deleted IDs
   (so re-reads don't resurrect user-deleted tasks), and provides
   HasExternalChanges/MergeFromDisk.  Save() now auto-merges before
   writing.  ID conflicts (same ID, different task) are resolved by
   reassigning the in-memory task to a fresh ID.

3. Idle polling in TKanbanUI.Run: every ~2 seconds (20 idle ReadKey
   cycles at VTIME=1), checks HasExternalChanges and merges new tasks
   with a status bar notification.

compiler/src/main/pascal/uCodeGenQBE.pas

@@ -8043,6 +8043,14 @@ begin
         Exit(T);
       end;
 
+      if SameText(FC.Name,'FileAge') then
+      begin
+        L := EmitExpr(TASTExpr(FC.Args.Items[0]));
+        T := AllocTemp;
+        EmitLine(Format('  %s =l call $_FileAge(l %s)', [T, L]));
+        Exit(T);
+      end;
+
       { Environment and process }
       if SameText(FC.Name,'GetEnvVar') or SameText(FC.Name,'GetEnvironmentVariable') then
       begin

compiler/src/main/pascal/uSemantic.pas

@@ -7238,6 +7238,16 @@ begin
     Exit;
   end;
 
+  if SameText(AExpr.Name, 'FileAge') then
+  begin
+    if AExpr.Args.Count <> 1 then
+      SemanticError('FileAge requires exactly 1 argument', AExpr.Line, AExpr.Col);
+    AnalyseExpr(TASTExpr(AExpr.Args.Items[0]));
+    Result := FTable.TypeInt64;
+    AExpr.ResolvedType := Result;
+    Exit;
+  end;
+
   if SameText(AExpr.Name, 'ForceDirectories') then
   begin
     if AExpr.Args.Count <> 1 then

compiler/src/main/pascal/uSymbolTable.pas

@@ -1593,6 +1593,7 @@ begin
   Sym := TSymbol.Create('WriteFile',  skProcedure, nil);          Define(Sym);
   Sym := TSymbol.Create('AppendFile', skProcedure, nil);          Define(Sym);
   Sym := TSymbol.Create('FileExists',             skFunction,  FTypeBoolean); Define(Sym);
+  Sym := TSymbol.Create('FileAge',               skFunction,  FTypeInt64);   Define(Sym);
   Sym := TSymbol.Create('DeleteFile',             skProcedure, nil);          Define(Sym);
   Sym := TSymbol.Create('CurrentExceptionMessage', skFunction,  FTypeString);  Define(Sym);
   { Environment and process }

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

@@ -47,6 +47,7 @@ type
     procedure TestRun_BoolToStr_TrueAndFalse;
     procedure TestRun_PlatformConstants;
     procedure TestRun_GetCurrentDir_ReturnsNonEmpty;
+    procedure TestRun_FileAge_ReturnsTimestamp;
   end;
 
 implementation
@@ -551,6 +552,17 @@ const
         end.
         ''';
 
+  SrcFileAge =
+    '''
+        program P;
+        var Age: Int64;
+        begin
+          Age := FileAge(ParamStr(1));
+          WriteLn(Age > 0);
+          WriteLn(FileAge('__no_such_file_xyz__'))
+        end.
+        ''';
+
 procedure TE2ESysUtilsTests.TestRun_RenameFile_Works;
 var
   Output: string;
@@ -676,6 +688,35 @@ begin
   AssertEquals('GetCurrentDir non-empty', 'True', Trim(Output));
 end;
 
+procedure TE2ESysUtilsTests.TestRun_FileAge_ReturnsTimestamp;
+var
+  Output: string;
+  RCode: Integer;
+  TmpFile: string;
+  Lines: TStringList;
+begin
+  if not ToolchainAvailable then begin Ignore('toolchain unavailable'); Exit; end;
+  TmpFile := GetTempFileName('', 'blaise_fileage_test');
+  Lines := TStringList.Create;
+  Lines.Add('x');
+  Lines.SaveToFile(TmpFile);
+  Lines.Free;
+  try
+    AssertTrue('compile+run',
+      CompileAndRun(SrcFileAge, Output, RCode, [TmpFile]));
+    Lines := TStringList.Create;
+    try
+      Lines.Text := Trim(Output);
+      AssertEquals('existing file age > 0', 'True', Lines.Strings[0]);
+      AssertEquals('missing file age = -1', '-1', Lines.Strings[1]);
+    finally
+      Lines.Free;
+    end;
+  finally
+    if FileExists(TmpFile) then DeleteFile(TmpFile);
+  end;
+end;
+
 initialization
   RegisterTest(TE2ESysUtilsTests);
 

compiler/src/test/pascal/cp.test.selfhosting.pas

@@ -52,6 +52,8 @@ type
     procedure TestCodegen_ReadFile_CallsRTL;
     procedure TestCodegen_WriteFile_CallsRTL;
     procedure TestCodegen_FileExists_CallsRTL;
+    procedure TestSemantic_FileAge_ReturnsInt64;
+    procedure TestCodegen_FileAge_CallsRTL;
 
     { ------------------------------------------------------------------ }
     { GetEnvVar / Exec / Halt (Gap 2 — environment and process)          }
@@ -211,6 +213,15 @@ const
         end.
         ''';
 
+  SrcFileAge =
+    '''
+        program P;
+        var A: Int64;
+        begin
+          A := FileAge('test.txt')
+        end.
+        ''';
+
   { Gap 2: environment and process }
   SrcGetEnvVar =
     '''
@@ -501,6 +512,36 @@ begin
   AssertTrue('FileExists calls _FileExists', Pos('_FileExists', IR) > 0);
 end;
 
+procedure TSelfHostingTests.TestSemantic_FileAge_ReturnsInt64;
+var
+  Lex:  TLexer;
+  Par:  TParser;
+  SA:   TSemanticAnalyser;
+  Prog: TProgram;
+  Ass:  TAssignment;
+begin
+  Lex  := TLexer.Create(SrcFileAge);
+  Par  := TParser.Create(Lex);
+  Prog := Par.Parse;
+  Par.Free;
+  Lex.Free;
+  SA   := TSemanticAnalyser.Create;
+  SA.Analyse(Prog);
+  SA.Free;
+  Ass := TAssignment(Prog.Block.Stmts[0]);
+  AssertEquals('FileAge returns Int64',
+    Ord(tyInt64), Ord(Ass.Expr.ResolvedType.Kind));
+  Prog.Free;
+end;
+
+procedure TSelfHostingTests.TestCodegen_FileAge_CallsRTL;
+var
+  IR: string;
+begin
+  IR := GenIR(SrcFileAge);
+  AssertTrue('FileAge calls _FileAge', Pos('_FileAge', IR) > 0);
+end;
+
 { ------------------------------------------------------------------ }
 { Gap 2: environment and process                                        }
 { ------------------------------------------------------------------ }

runtime/src/main/pascal/rtl.platform.pas

@@ -32,6 +32,7 @@ type
     function ReadFile(const APath: string): string; virtual; abstract;
     procedure WriteFile(const APath, AContent: string); virtual; abstract;
     procedure AppendFile(const APath, AContent: string); virtual; abstract;
+    function FileAge(const APath: string): Int64; virtual; abstract;
 
     { Directory operations }
     function DirectoryExists(const APath: string): Boolean; virtual; abstract;

runtime/src/main/pascal/rtl.platform.posix.pas

@@ -40,6 +40,7 @@ type
     function ReadFile(const APath: string): string; override;
     procedure WriteFile(const APath, AContent: string); override;
     procedure AppendFile(const APath, AContent: string); override;
+    function FileAge(const APath: string): Int64; override;
 
     { Directory operations }
     function DirectoryExists(const APath: string): Boolean; override;
@@ -220,6 +221,7 @@ function  _RenameFile(OldPath, NewPath: Pointer): Integer;
 function  _ReadFile(Path: Pointer): Pointer;
 procedure _WriteFile(Path, Content: Pointer);
 procedure _AppendFile(Path, Content: Pointer);
+function  _FileAge(Path: Pointer): Int64;
 
 { Directory operations }
 function  _DirectoryExists(Path: Pointer): Integer;
@@ -499,6 +501,14 @@ begin
   libc_close(Fd);
 end;
 
+function TRtlPlatformPosix.FileAge(const APath: string): Int64;
+var
+  St: TStatBuf;
+begin
+  if libc_stat(StrData(Pointer(APath)), @St) <> 0 then begin Result := -1; Exit end;
+  Result := St.Mtime;
+end;
+
 { ================================================================== }
 { TRtlPlatformPosix — Directory operations                            }
 { ================================================================== }
@@ -1205,6 +1215,11 @@ begin
   GRtlPlatform.AppendFile(string(PChar(Path)), string(PChar(Content)));
 end;
 
+function _FileAge(Path: Pointer): Int64;
+begin
+  Result := GRtlPlatform.FileAge(string(PChar(Path)));
+end;
+
 function _DirectoryExists(Path: Pointer): Integer;
 begin
   if GRtlPlatform.DirectoryExists(string(PChar(Path))) then Result := 1 else Result := 0;

tools/kanban/src/main/pascal/kanban.data.pas

@@ -15,6 +15,10 @@ uses Classes, Contnrs, StrUtils, DateUtils;
 type
   TTaskStatus = (tsTodo, tsInProgress, tsDone);
 
+  TIntHolder = class
+    FValue: Integer;
+  end;
+
   TTask = class
     FId: Integer;
     FTitle: string;
@@ -32,9 +36,12 @@ type
     FTasks: TObjectList;
     FNextId: Integer;
     FFilePath: string;
+    FLastMtime: Int64;
+    FDeletedIds: TObjectList;
     function GetCount: Integer;
     procedure ParseLine(const Line: string; CurrentStatus: TTaskStatus);
     function FormatTask(Task: TTask): string;
+    function IsDeleted(AId: Integer): Boolean;
   public
     constructor Create(const AFilePath: string);
     destructor Destroy; override;
@@ -50,6 +57,8 @@ type
     function HasDetail(AId: Integer): Boolean;
     function LoadDetail(AId: Integer): string;
     procedure SaveDetail(AId: Integer; const AContent: string);
+    function HasExternalChanges: Boolean;
+    function MergeFromDisk: Integer;
     property Count: Integer read GetCount;
     property FilePath: string read FFilePath;
   end;
@@ -63,11 +72,14 @@ begin
   inherited Create;
   FFilePath := AFilePath;
   FTasks := TObjectList.Create(True);
-  FNextId := 1
+  FDeletedIds := TObjectList.Create(True);
+  FNextId := 1;
+  FLastMtime := -1
 end;
 
 destructor TBoard.Destroy;
 begin
+  FDeletedIds.Free;
   FTasks.Free;
   inherited Destroy
 end;
@@ -209,7 +221,8 @@ begin
     end
   finally
     Lines.Free
-  end
+  end;
+  FLastMtime := FileAge(FFilePath)
 end;
 
 procedure TBoard.Save;
@@ -218,6 +231,8 @@ var
   I: Integer;
   Task: TTask;
 begin
+  if Self.HasExternalChanges then
+    Self.MergeFromDisk;
   Lines := TStringList.Create;
   try
     Lines.Add('#next-id: ' + IntToStr(FNextId));
@@ -257,7 +272,8 @@ begin
     Lines.SaveToFile(FFilePath)
   finally
     Lines.Free
-  end
+  end;
+  FLastMtime := FileAge(FFilePath)
 end;
 
 function TBoard.AddTask(const ATitle: string; AStatus: TTaskStatus): TTask;
@@ -277,11 +293,26 @@ begin
   FTasks.Add(Result)
 end;
 
+function TBoard.IsDeleted(AId: Integer): Boolean;
+var
+  I: Integer;
+begin
+  I := 0;
+  while I < FDeletedIds.Count do
+  begin
+    if TIntHolder(FDeletedIds.Get(I)).FValue = AId then
+      Exit(True);
+    I := I + 1
+  end;
+  Result := False
+end;
+
 procedure TBoard.DeleteTask(AId: Integer);
 var
   I: Integer;
   Task: TTask;
   DetailPath: string;
+  Holder: TIntHolder;
 begin
   I := 0;
   while I < FTasks.Count do
@@ -293,6 +324,9 @@ begin
       if FileExists(DetailPath) then
         DeleteFile(DetailPath);
       FTasks.Delete(I);
+      Holder := TIntHolder.Create;
+      Holder.FValue := AId;
+      FDeletedIds.Add(Holder);
       Exit
     end;
     I := I + 1
@@ -395,6 +429,73 @@ begin
   WriteFile(Self.GetDetailPath(AId), AContent)
 end;
 
+function TBoard.HasExternalChanges: Boolean;
+var
+  CurrentMtime: Int64;
+begin
+  CurrentMtime := FileAge(FFilePath);
+  Result := (CurrentMtime <> -1) and (CurrentMtime <> FLastMtime)
+end;
+
+function TBoard.MergeFromDisk: Integer;
+var
+  DiskBoard: TBoard;
+  I, Merged, MaxId: Integer;
+  DiskTask, MemTask, NewTask: TTask;
+begin
+  Merged := 0;
+  DiskBoard := TBoard.Create(FFilePath);
+  try
+    DiskBoard.Load;
+
+    MaxId := FNextId;
+    if DiskBoard.FNextId > MaxId then
+      MaxId := DiskBoard.FNextId;
+
+    I := 0;
+    while I < DiskBoard.FTasks.Count do
+    begin
+      DiskTask := TTask(DiskBoard.FTasks.Get(I));
+      if Self.IsDeleted(DiskTask.FId) then
+      begin
+        I := I + 1;
+        Continue
+      end;
+      MemTask := Self.FindById(DiskTask.FId);
+      if MemTask = nil then
+      begin
+        NewTask := TTask.Create;
+        NewTask.FId := DiskTask.FId;
+        NewTask.FTitle := DiskTask.FTitle;
+        NewTask.FStatus := DiskTask.FStatus;
+        NewTask.FCreated := DiskTask.FCreated;
+        NewTask.FPriority := DiskTask.FPriority;
+        FTasks.Add(NewTask);
+        Merged := Merged + 1
+      end
+      else if MemTask.FTitle <> DiskTask.FTitle then
+      begin
+        MemTask.FId := MaxId;
+        MaxId := MaxId + 1;
+        NewTask := TTask.Create;
+        NewTask.FId := DiskTask.FId;
+        NewTask.FTitle := DiskTask.FTitle;
+        NewTask.FStatus := DiskTask.FStatus;
+        NewTask.FCreated := DiskTask.FCreated;
+        NewTask.FPriority := DiskTask.FPriority;
+        FTasks.Add(NewTask);
+        Merged := Merged + 1
+      end;
+      I := I + 1
+    end;
+    FNextId := MaxId
+  finally
+    DiskBoard.Free
+  end;
+  FLastMtime := FileAge(FFilePath);
+  Result := Merged
+end;
+
 function CreatedToLocalDate(const AUtcStr: string): string;
 var
   UtcDT: TDateTime;

tools/kanban/src/main/pascal/kanban.ui.pas

@@ -28,6 +28,7 @@ type
     FInputPrompt: string;
     FStatusMsg: string;
     FNeedsRedraw: Boolean;
+    FPollCounter: Integer;
     procedure DrawBoard;
     procedure DrawColumn(ColIndex: Integer; Row, Col, Width, Height: Integer);
     procedure DrawStatusBar;
@@ -64,7 +65,8 @@ begin
   FInputBuf := '';
   FInputPrompt := '';
   FStatusMsg := 'q:quit  a:add  d:delete  Enter:details  h/l:move task  ?:help';
-  FNeedsRedraw := True
+  FNeedsRedraw := True;
+  FPollCounter := 0
 end;
 
 function TKanbanUI.ColumnTitle(ColIndex: Integer): string;
@@ -343,6 +345,7 @@ begin
     FTerm.ShowCursor;
     FTerm.BufFlush;
     FTerm.DisableRawMode;
+    FBoard.MergeFromDisk;
     FBoard.Save;
     Halt(0)
   end;
@@ -594,7 +597,7 @@ end;
 
 procedure TKanbanUI.Run;
 var
-  Key: Integer;
+  Key, Merged: Integer;
 begin
   FTerm.EnableRawMode;
   try
@@ -611,6 +614,27 @@ begin
 
       Key := FTerm.ReadKey;
 
+      if Key = KEY_NONE then
+      begin
+        FPollCounter := FPollCounter + 1;
+        if FPollCounter >= 20 then
+        begin
+          FPollCounter := 0;
+          if FBoard.HasExternalChanges then
+          begin
+            Merged := FBoard.MergeFromDisk;
+            if Merged > 0 then
+            begin
+              FStatusMsg := 'Reloaded ' + IntToStr(Merged) + ' new task(s) from disk';
+              Self.ClampRow;
+              FNeedsRedraw := True
+            end
+          end
+        end
+      end
+      else
+        FPollCounter := 0;
+
       if FViewMode = vmBoard then
         Self.HandleBoardKey(Key)
       else if FViewMode = vmDetail then