Consolidate duplicated user selection logic into shared helper with sync mechanism

SHARED_CODE.md

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+# Shared Code Maintenance
+
+This document explains how shared code is maintained across features in this repository.
+
+## Problem
+
+Multiple features need the same helper functions (e.g., user selection logic). The devcontainer specification currently packages each feature independently and doesn't support sharing code between features at runtime.
+
+## Solution
+
+We maintain a **single source of truth** with a **sync mechanism** to deploy to each feature:
+
+### Single Source
+- **Location**: `scripts/lib/common-setup.sh`
+- **Contains**: Shared helper functions (currently user selection logic)
+- **Maintenance**: All updates happen here
+
+### Deployment
+- **Mechanism**: `scripts/sync-common-setup.sh`
+- **Target**: Copies to each feature's `_lib/` directory
+- **Reason**: Devcontainer packaging requires files to be within each feature's directory
+
+## Workflow
+
+### Making Changes
+
+1. **Edit the source**: Modify `scripts/lib/common-setup.sh`
+2. **Test**: Run `bash test/_lib/test-common-setup.sh`
+3. **Sync**: Run `./scripts/sync-common-setup.sh`
+4. **Commit**: Include both source and deployed copies
+
+```bash
+# Edit the source
+vim scripts/lib/common-setup.sh
+
+# Test
+bash test/_lib/test-common-setup.sh
+
+# Deploy to all features
+./scripts/sync-common-setup.sh
+
+# Commit everything
+git add scripts/lib/common-setup.sh src/*/_lib/common-setup.sh
+git commit -m "Update common-setup.sh helper function"
+```
+
+### Verification
+
+The sync script is idempotent - running it multiple times with the same source produces the same result. After syncing, you can verify:
+
+```bash
+# Check that all copies are identical
+for f in src/*/_lib/common-setup.sh; do
+    diff -q scripts/lib/common-setup.sh "$f" || echo "MISMATCH: $f"
+done
+```
+
+## Why Not Use Shared Files?
+
+The devcontainer CLI packages each feature independently. When a feature is installed:
+
+1. Only files within the feature's directory are included in the package
+2. Parent directories (`../common`) are not accessible
+3. Hidden directories (`.common`) are excluded from packaging
+4. Sibling feature directories are not accessible
+
+This is a design decision in the devcontainer specification to ensure features are portable and self-contained.
+
+## Future
+
+The devcontainer spec has a proposal for an `include` property in `devcontainer-feature.json` ([spec#129](https://github.com/devcontainers/spec/issues/129)) that would enable native code sharing. Once implemented, the sync mechanism can be removed in favor of declarative includes:
+
+```json
+{
+  "id": "my-feature",
+  "include": ["../../scripts/lib/common-setup.sh"]
+}
+```
+
+## Current Implementation
+
+As of this PR:
+- **Source**: `scripts/lib/common-setup.sh` (87 lines)
+- **Deployed**: 17 features, each with `src/FEATURE/_lib/common-setup.sh`
+- **Sync Script**: `scripts/sync-common-setup.sh`
+- **Tests**: `test/_lib/test-common-setup.sh` (14 test cases)
+- **Benefits**: Eliminated ~188 lines of inline duplicated logic from install scripts
+
+## References
+
+- [Devcontainer Spec Issue #129 - Share code between features](https://github.com/devcontainers/spec/issues/129)
+- [Features Library Proposal](https://github.com/devcontainers/spec/blob/main/proposals/features-library.md)
+- Test documentation: `test/_lib/README.md`
+- Sync script documentation: `scripts/README.md`

scripts/README.md

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+# Shared Feature Code
+
+This directory contains code that is shared across multiple features.
+
+## Structure
+
+```
+scripts/
+├── lib/
+│   └── common-setup.sh         # Source of truth for user selection helper
+└── sync-common-setup.sh         # Script to deploy helper to all features
+```
+
+## Maintenance
+
+### The Source of Truth
+
+**`scripts/lib/common-setup.sh`** is the single source of truth for the user selection helper function. All modifications should be made to this file.
+
+### Deploying Changes
+
+Due to the devcontainer CLI's packaging behavior (each feature is packaged independently), the helper must be deployed to each feature's `_lib/` directory. We maintain this through a sync script:
+
+```bash
+./scripts/sync-common-setup.sh
+```
+
+This copies `scripts/lib/common-setup.sh` to all features:
+- `src/anaconda/_lib/common-setup.sh`
+- `src/docker-in-docker/_lib/common-setup.sh`
+- etc.
+
+### Workflow
+
+1. **Edit**: Make changes to `scripts/lib/common-setup.sh`
+2. **Test**: Run `bash test/_lib/test-common-setup.sh` to verify
+3. **Sync**: Run `./scripts/sync-common-setup.sh` to deploy to all features
+4. **Commit**: Commit both the source and all copies together
+
+### Why Copies?
+
+The devcontainer CLI packages each feature independently:
+- Parent directories are not included in the build context
+- Hidden directories (`.common`) are not included
+- Sibling directories are not accessible
+
+Therefore, each feature needs its own copy of the helper to ensure it's available at runtime during feature installation.
+
+## Testing
+
+Tests are located in `test/_lib/` and reference the anaconda feature's copy as the source:
+
+```bash
+bash test/_lib/test-common-setup.sh
+```
+
+## Future
+
+This approach is a workaround for the current limitation. The devcontainer spec has a proposal for an `include` property in `devcontainer-feature.json` that would allow native code sharing (see [devcontainers/spec#129](https://github.com/devcontainers/spec/issues/129)). Once implemented, this sync mechanism can be removed.

scripts/lib/common-setup.sh

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+#!/bin/bash
+#-------------------------------------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See https://github.com/devcontainers/features/blob/main/LICENSE for license information.
+#-------------------------------------------------------------------------------------------------------------------------
+#
+# Helper script for common feature setup tasks, including user selection logic.
+# Maintainer: The Dev Container spec maintainers
+
+# Determine the appropriate non-root user
+# Usage: determine_user_from_input USERNAME [FALLBACK_USER]
+#
+# This function resolves the USERNAME variable based on the input value:
+# - If USERNAME is "auto" or "automatic", it will detect an existing non-root user
+# - If USERNAME is "none" or doesn't exist, it will fall back to root
+# - Otherwise, it validates the specified USERNAME exists
+#
+# Arguments:
+#   USERNAME - The username input (typically from feature configuration)
+#   FALLBACK_USER - Optional fallback user when no user is found in automatic mode (defaults to "root")
+#
+# Returns:
+#   The resolved username is printed to stdout
+#
+# Examples:
+#   USERNAME=$(determine_user_from_input "automatic")
+#   USERNAME=$(determine_user_from_input "vscode")
+#   USERNAME=$(determine_user_from_input "auto" "vscode")
+#
+determine_user_from_input() {
+    local input_username="${1:-automatic}"
+    local fallback_user="${2:-root}"
+    local resolved_username=""
+
+    if [ "${input_username}" = "auto" ] || [ "${input_username}" = "automatic" ]; then
+        # Automatic mode: try to detect an existing non-root user
+
+        # First, check if _REMOTE_USER is set and is not root
+        if [ -n "${_REMOTE_USER:-}" ] && [ "${_REMOTE_USER}" != "root" ]; then
+            # Verify the user exists before using it
+            if id -u "${_REMOTE_USER}" > /dev/null 2>&1; then
+                resolved_username="${_REMOTE_USER}"
+            else
+                # _REMOTE_USER doesn't exist, fall through to normal detection
+                resolved_username=""
+            fi
+        fi
+
+        # If we didn't resolve via _REMOTE_USER, try to find a non-root user
+        if [ -z "${resolved_username}" ]; then
+            # Try to find a non-root user from a list of common usernames
+            # The list includes: devcontainer, vscode, node, codespace, and the user with UID 1000
+            local possible_users=("devcontainer" "vscode" "node" "codespace" "$(awk -v val=1000 -F ":" '$3==val{print $1}' /etc/passwd 2>/dev/null || echo '')")
+
+            for current_user in "${possible_users[@]}"; do
+                # Skip empty entries
+                if [ -z "${current_user}" ]; then
+                    continue
+                fi
+
+                # Check if user exists
+                if id -u "${current_user}" > /dev/null 2>&1; then
+                    resolved_username="${current_user}"
+                    break
+                fi
+            done
+
+            # If no user found, use the fallback
+            if [ -z "${resolved_username}" ]; then
+                resolved_username="${fallback_user}"
+            fi
+        fi
+    elif [ "${input_username}" = "none" ]; then
+        # Explicit "none" means use root
+        resolved_username="root"
+    else
+        # Specific username provided - validate it exists
+        if id -u "${input_username}" > /dev/null 2>&1; then
+            resolved_username="${input_username}"
+        else
+            # User doesn't exist, fall back to root
+            resolved_username="root"
+        fi
+    fi
+
+    echo "${resolved_username}"
+}

scripts/sync-common-setup.sh

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+#!/bin/bash
+#-------------------------------------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See https://github.com/devcontainers/features/blob/main/LICENSE for license information.
+#-------------------------------------------------------------------------------------------------------------------------
+#
+# Script to sync common-setup.sh from the source to all feature _lib directories
+# This maintains a single source of truth while deploying to each feature for packaging
+#
+# Usage: ./scripts/sync-common-setup.sh
+#
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
+
+# The source of truth for common-setup.sh
+SOURCE_FILE="${REPO_ROOT}/scripts/lib/common-setup.sh"
+
+# Features that use the common-setup helper
+# Note: common-utils is excluded because it creates users (different semantics)
+FEATURES=(
+    "anaconda"
+    "conda"
+    "desktop-lite"
+    "docker-in-docker"
+    "docker-outside-of-docker"
+    "go"
+    "hugo"
+    "java"
+    "kubectl-helm-minikube"
+    "node"
+    "oryx"
+    "php"
+    "python"
+    "ruby"
+    "rust"
+    "sshd"
+)
+
+echo "Syncing common-setup.sh to all features..."
+echo "Source: ${SOURCE_FILE}"
+echo ""
+
+if [ ! -f "${SOURCE_FILE}" ]; then
+    echo "Error: Source file not found: ${SOURCE_FILE}"
+    exit 1
+fi
+
+UPDATED_COUNT=0
+
+for feature in "${FEATURES[@]}"; do
+    TARGET_DIR="${REPO_ROOT}/src/${feature}/_lib"
+    TARGET_FILE="${TARGET_DIR}/common-setup.sh"
+
+    # Create _lib directory if it doesn't exist
+    mkdir -p "${TARGET_DIR}"
+
+    # Copy the file
+    cp "${SOURCE_FILE}" "${TARGET_FILE}"
+
+    echo "✓ Synced to src/${feature}/_lib/common-setup.sh"
+    UPDATED_COUNT=$((UPDATED_COUNT + 1))
+done
+
+echo ""
+echo "======================================"
+echo "Sync complete!"
+echo "Updated ${UPDATED_COUNT} features"
+echo "======================================"
+echo ""
+echo "Note: After running this script, commit the changes:"
+echo "  git add src/*/lib/common-setup.sh"
+echo "  git commit -m 'Sync common-setup.sh to all features'"