Ensure headers are self-contained after IWYU cleanup

Downstream projects include eckit headers in arbitrary combinations
and orders. A header that silently depends on a transitive include
will break when unrelated changes elsewhere shuffle include graphs.

Run IWYU 0.25 across the codebase to add missing direct includes
and remove unnecessary ones, so every header compiles on its own.

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

Author: Ozaq

.clang-format

@@ -59,12 +59,17 @@ ForEachMacros:
   - foreach
   - Q_FOREACH
   - BOOST_FOREACH
+IncludeBlocks: Regroup
 IncludeCategories:
-  - Regex: '^<.*\.h>'
+  # eckit headers
+  - Regex: '"eckit/.*"'
     Priority: 1
-  - Regex: "^<.*"
+    SortPriority: 0
+  # Other project headers (quoted)
+  - Regex: '".*"'
     Priority: 2
-  - Regex: ".*"
+  # System / third-party headers (angle brackets)
+  - Regex: '<.*>'
     Priority: 3
 IncludeIsMainRegex: "([-_](test|unittest))?$"
 IndentCaseLabels: true

regressions/ECKIT-166.cc

@@ -5,11 +5,11 @@ BUG ECKIT-166
 
 */
 
-#include <iostream>
-
 #include "eckit/mpi/Comm.h"
 #include "eckit/runtime/Main.h"
 
+#include <iostream>
+
 using namespace eckit;
 
 void run(int argc, char** argv) {

regressions/ECKIT-175.cc

@@ -28,14 +28,15 @@ BUG ECKIT-175
 
 */
 
-#include <cstdlib>
-#include <iostream>
-#include <map>
-
+#include "eckit/log/Channel.h"
 #include "eckit/log/Log.h"
 #include "eckit/runtime/Main.h"
 #include "eckit/runtime/Tool.h"
 
+#include <cstdlib>
+#include <iostream>
+#include <string>
+
 using namespace eckit;
 
 void myrun() {

regressions/ECKIT-221.cc

@@ -7,16 +7,18 @@ FEATURE ECKIT-221
 
 */
 
-#include <cstdlib>
-#include <iostream>
-#include <map>
-#include <memory>
-
+#include "eckit/filesystem/PathName.h"
 #include "eckit/io/DataHandle.h"
+#include "eckit/io/SharedBuffer.h"
 #include "eckit/mpi/Comm.h"
 #include "eckit/runtime/Tool.h"
 #include "eckit/utils/Translator.h"
 
+#include <cstdlib>
+#include <iostream>
+#include <memory>
+#include <string>
+
 using namespace eckit;
 
 class MyTool : public Tool {

src/eckit/bases/Loader.h

@@ -12,8 +12,6 @@
 // Baudouin Raoult - ECMWF Jul 96
 
 #pragma once
-#include "eckit/eckit.h"
-
 #include "eckit/container/ClassExtent.h"
 
 //-----------------------------------------------------------------------------

src/eckit/cmd/AliasCmd.cc

@@ -9,7 +9,11 @@
  */
 
 #include "eckit/cmd/AliasCmd.h"
+
+#include "eckit/cmd/Arg.h"
+#include "eckit/cmd/CmdArg.h"
 #include "eckit/cmd/CmdParser.h"
+#include "eckit/value/Value.h"
 
 //----------------------------------------------------------------------------------------------------------------------
 

src/eckit/cmd/AliasCmd.h

@@ -14,6 +14,9 @@
 #pragma once
 #include "eckit/cmd/CmdResource.h"
 
+#include <iosfwd>
+#include <string>
+
 
 namespace eckit {
 

src/eckit/cmd/Arg.cc

@@ -10,6 +10,7 @@
 
 #include "eckit/cmd/Arg.h"
 
+#include <cstddef>
 #include <iostream>
 
 namespace eckit {

src/eckit/cmd/CmdApplication.cc

@@ -12,16 +12,25 @@
 /// @author Florian Rathgeber
 /// @date   June 2015
 
-#include <unistd.h>
-#include <fstream>
-
 #include "eckit/cmd/CmdApplication.h"
+
 #include "eckit/config/Resource.h"
 #include "eckit/filesystem/PathName.h"
 #include "eckit/io/SockBuf.h"
+#include "eckit/log/Channel.h"
+#include "eckit/log/CodeLocation.h"
+#include "eckit/log/Log.h"
 #include "eckit/net/TCPServer.h"
+#include "eckit/net/TCPSocket.h"
 #include "eckit/runtime/Main.h"
 #include "eckit/runtime/Monitor.h"
+#include "eckit/types/Types.h"
+
+#include <exception>
+#include <fstream>
+#include <iostream>
+#include <unistd.h>
+#include <vector>
 
 namespace eckit {
 

src/eckit/cmd/CmdApplication.h

@@ -15,6 +15,9 @@
 #pragma once
 #include "eckit/cmd/CmdParser.h"
 
+#include <iosfwd>
+#include <string>
+
 namespace eckit {
 
 //----------------------------------------------------------------------------------------------------------------------