Add codespace setup for companion repositories

.devcontainer/codespace.code-workspace

@@ -0,0 +1,119 @@
+{
+    "folders": [
+        {
+            "name": "Phlex",
+            "path": "/workspaces/phlex"
+        },
+        {
+            "name": "Phlex Design",
+            "path": "/workspaces/phlex-design"
+        },
+        {
+            "name": "Phlex Examples",
+            "path": "/workspaces/phlex-examples"
+        },
+        {
+            "name": "Phlex Coding Guidelines",
+            "path": "/workspaces/phlex-coding-guidelines"
+        },
+        {
+            "name": "Phlex Spack Recipes",
+            "path": "/workspaces/phlex-spack-recipes"
+        }
+    ],
+    "settings": {
+        "files.associations": {
+            "*.yml": "yaml",
+            "*.yaml": "yaml"
+        },
+        "files.exclude": {
+            "**/local/.*/**": true,
+            "**/local/*/": true
+        },
+        "search.exclude": {
+            "**/local/.*/**": true,
+            "**/local/*/": true,
+            "**/build/_deps/**": true,
+            "**/build/CMakeFiles/**": true
+        },
+        "files.watcherExclude": {
+            "**/local/.*/**": true,
+            "**/local/*/": true,
+            "**/build/_deps/**": true,
+            "**/build/CMakeFiles/**": true
+        },
+        "cmake.sourceDirectory": "${workspaceFolder:Phlex}",
+        "cmake.buildDirectory": "${workspaceFolder:Phlex}/build",
+        "cmake.useCMakePresets": "always",
+        "cmake.generator": "Ninja",
+        "C_Cpp.default.cStandard": "c17",
+        "C_Cpp.default.cppStandard": "c++23",
+        "C_Cpp.default.intelliSenseMode": "linux-gcc-x64",
+        "C_Cpp.default.compileCommands": "${workspaceFolder:Phlex}/build/compile_commands.json",
+        "C_Cpp.exclusionPolicy": "checkFolders",
+        "C_Cpp.files.exclude": {
+            "**/local/.*/**": true,
+            "**/local/*/": true,
+            "**/build/_deps/**": true,
+            "**/build/CMakeFiles/**": true
+        },
+        "python.languageServer": "Pylance",
+        "python.analysis.typeCheckingMode": "basic",
+        "python.analysis.diagnosticMode": "workspace",
+        "python.analysis.exclude": [
+            "**/local/.*/**",
+            "**/local/*/",
+            "**/build/_deps/**",
+            "**/build/CMakeFiles/**"
+        ],
+        "python.analysis.ignore": [
+            "**/local/.*/**",
+            "**/local/*/",
+            "**/build/_deps/**",
+            "**/build/CMakeFiles/**"
+        ],
+        "flake8.enabled": false,
+        "[python]": {
+            "editor.formatOnSave": true,
+            "editor.defaultFormatter": "charliermarsh.ruff",
+            "editor.codeActionsOnSave": {
+                "source.organizeImports.ruff": "explicit",
+                "source.fixAll.ruff": "explicit"
+            }
+        },
+        "yaml.schemas": {
+            "https://json.schemastore.org/github-workflow.json": "./.github/workflows/*"
+        }
+    },
+    "extensions": {
+        "recommendations": [
+            "ms-vscode.cmake-tools",
+            "ms-vscode.cpptools",
+            "ms-vscode.cpptools-extension-pack",
+            "twxs.cmake",
+            "ms-vscode.vscode-json",
+            "redhat.vscode-yaml",
+            "charliermarsh.ruff",
+            "github.vscode-github-actions",
+            "github.copilot",
+            "github.copilot-chat",
+            "github.vscode-pull-request-github",
+            "ms-vscode.hexeditor"
+        ],
+        "unwantedRecommendations": [
+            "reditorsupport.r",
+            "ms-vscode.r",
+            "ikuyadeu.r",
+            "ms-vscode.r-debugger",
+            "vscjava.vscode-java-pack",
+            "redhat.java",
+            "vscjava.vscode-java-debug",
+            "vscjava.vscode-java-test",
+            "vscjava.vscode-maven",
+            "vscjava.vscode-gradle",
+            "ms-python.python",
+            "ms-toolsai.jupyter",
+            "ms-python.flake8"
+        ]
+    }
+}

.devcontainer/devcontainer.json

@@ -14,6 +14,7 @@
     "mounts": [
         "source=${env:HOME}/.config/gh,target=/home/vscode/.config/gh,type=bind,readonly"
     ],
+    "onCreateCommand": "bash .devcontainer/setup-repos.sh /workspaces",
     "customizations": {
         "vscode": {
             "settings": {
@@ -38,7 +39,7 @@
                 "cmake.ctestPath": "${workspaceFolder}/.devcontainer/ctest_wrapper.sh",
                 "cmake.generator": "Ninja",
                 "C_Cpp.default.cStandard": "c17",
-                "C_Cpp.default.cppStandard": "c++20",
+                "C_Cpp.default.cppStandard": "c++23",
                 "C_Cpp.default.intelliSenseMode": "linux-gcc-x64",
                 "C_Cpp.default.compileCommands": "${workspaceFolder}/build/compile_commands.json",
                 "python.languageServer": "Pylance",

.devcontainer/setup-repos.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+
+# Clone companion repositories into the codespace so they are available
+# for reference by developers and AI agents.
+#
+# Intended to be called from devcontainer.json onCreateCommand.
+
+set -euo pipefail
+
+WORKSPACE_ROOT="${1:-/workspaces}"
+
+if [ ! -d "$WORKSPACE_ROOT" ]; then
+  echo "Error: workspace root does not exist: $WORKSPACE_ROOT" >&2
+  exit 1
+fi
+
+clone_if_absent() {
+  local repo=$1
+  local dest="${WORKSPACE_ROOT}/${repo}"
+  if [ -e "$dest/.git" ]; then
+    echo "Repository already present: $dest"
+    return
+  elif [ -e "$dest" ]; then
+    echo "WARNING: refusing to overwrite non-repository $dest:"
+    ls -ld "$dest"
+    return
+  fi
+  echo "Cloning Framework-R-D/${repo} into ${dest} ..."
+  local max_tries=5 current_try=0
+  while ! git clone --depth 1 "https://github.com/Framework-R-D/${repo}.git" "$dest"; do
+    (( ++current_try ))
+    echo "Attempt $current_try/$max_tries to clone $repo from GitHub FAILED"
+    (( current_try < max_tries )) || break
+    sleep 5
+  done
+  if (( current_try == max_tries )); then
+    echo "WARNING: unable to check out $repo to $dest from GitHub" 1>&2
+  fi
+}
+
+clone_if_absent phlex-design
+clone_if_absent phlex-examples
+clone_if_absent phlex-coding-guidelines
+clone_if_absent phlex-spack-recipes

.github/copilot-instructions.md

@@ -5,12 +5,29 @@
 ### Repository Ecosystem
 
 - **Primary Repository**: `Framework-R-D/phlex`
-- **Design & Documentation**: `Framework-R-D/phlex-design` (contains design docs, coding guidelines, etc.)
+- **Design & Documentation**: `Framework-R-D/phlex-design` (contains design and other documentation)
+- **Coding Guidelines**: `Framework-R-D/phlex-coding-guidelines` (coding guidelines for framework contributors)
+- **Examples**: `Framework-R-D/phlex-examples` (example user code demonstrating Phlex usage)
+- **Spack Recipes**: `Framework-R-D/phlex-spack-recipes` (Spack recipes for Phlex and dependencies)
 - **Dependencies**: Critical dependency on `FNALssi/cetmodules` for the build system.
 - **Container Images**:
   - `phlex-ci`: Used by automated CI checks.
   - `phlex-dev`: Used for VSCode devcontainers and local development.
 
+### Codespace Layout
+
+In a GitHub Codespace (or devcontainer), companion repositories are cloned
+automatically alongside the primary repository:
+
+- `/workspaces/phlex` — primary repository (workspace root)
+- `/workspaces/phlex-design` — design documentation
+- `/workspaces/phlex-examples` — example programs using Phlex
+- `/workspaces/phlex-coding-guidelines` — coding guidelines for contributors
+- `/workspaces/phlex-spack-recipes` — Spack recipes for Phlex and dependencies
+
+Use the multi-root workspace file `.devcontainer/codespace.code-workspace` to
+open all repositories in a single VS Code window.
+
 ### Development Workflow
 
 - **Model**: Fork-based development. Developers should work on branches within their own forks.

phlex.code-workspace

@@ -31,7 +31,7 @@
         "cmake.useCMakePresets": "always",
         "cmake.generator": "Ninja",
         "C_Cpp.default.cStandard": "c17",
-        "C_Cpp.default.cppStandard": "c++20",
+        "C_Cpp.default.cppStandard": "c++23",
         "C_Cpp.default.intelliSenseMode": "linux-gcc-x64",
         "C_Cpp.default.compileCommands": "${workspaceFolder}/build/compile_commands.json",
         "C_Cpp.exclusionPolicy": "checkFolders",