feat: add devcontainer for VS Code and GitHub Codespaces

.devcontainer/Dockerfile

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+# go-sqlcmd Development Container
+FROM mcr.microsoft.com/devcontainers/go:1.24-bookworm
+
+# Install additional OS packages
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get install -y curl libkrb5-dev gnupg2 \
+    && apt-get clean -y && rm -rf /var/lib/apt/lists/*
+
+# Install Microsoft ODBC driver and mssql-tools18 (legacy ODBC sqlcmd/bcp for compatibility testing)
+RUN curl -fsSL https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor -o /usr/share/keyrings/microsoft-prod.gpg \
+    && curl -fsSL https://packages.microsoft.com/config/debian/12/prod.list | tee /etc/apt/sources.list.d/mssql-release.list \
+    && apt-get update \
+    && ACCEPT_EULA=Y apt-get install -y msodbcsql18 mssql-tools18 unixodbc-dev \
+    && apt-get clean -y && rm -rf /var/lib/apt/lists/*
+ENV PATH="/opt/mssql-tools18/bin:${PATH}"
+
+# Install golangci-lint for code quality
+# Download pre-built binary with SHA256 checksum verification (supply chain security)
+# Supports both amd64 and arm64 architectures
+ARG GOLANGCI_LINT_VERSION=1.64.8
+ARG GOLANGCI_LINT_SHA256_AMD64=b6270687afb143d019f387c791cd2a6f1cb383be9b3124d241ca11bd3ce2e54e
+ARG GOLANGCI_LINT_SHA256_ARM64=a6ab58ebcb1c48572622146cdaec2956f56871038a54ed1149f1386e287789a5
+RUN ARCH=$(dpkg --print-architecture) \
+    && if [ "$ARCH" = "amd64" ]; then \
+         CHECKSUM="${GOLANGCI_LINT_SHA256_AMD64}"; \
+       elif [ "$ARCH" = "arm64" ]; then \
+         CHECKSUM="${GOLANGCI_LINT_SHA256_ARM64}"; \
+       else \
+         echo "Unsupported architecture: $ARCH" && exit 1; \
+       fi \
+    && curl -fsSLO "https://github.com/golangci/golangci-lint/releases/download/v${GOLANGCI_LINT_VERSION}/golangci-lint-${GOLANGCI_LINT_VERSION}-linux-${ARCH}.tar.gz" \
+    && echo "${CHECKSUM}  golangci-lint-${GOLANGCI_LINT_VERSION}-linux-${ARCH}.tar.gz" | sha256sum -c - \
+    && tar -xzf "golangci-lint-${GOLANGCI_LINT_VERSION}-linux-${ARCH}.tar.gz" \
+    && mv "golangci-lint-${GOLANGCI_LINT_VERSION}-linux-${ARCH}/golangci-lint" /usr/local/bin/ \
+    && rm -rf "golangci-lint-${GOLANGCI_LINT_VERSION}-linux-${ARCH}" "golangci-lint-${GOLANGCI_LINT_VERSION}-linux-${ARCH}.tar.gz" \
+    && golangci-lint --version
+
+# Install additional Go tools (pinned versions for reproducibility)
+RUN go install golang.org/x/tools/gopls@v0.18.1 \
+    && go install github.com/go-delve/delve/cmd/dlv@v1.24.1 \
+    && go install honnef.co/go/tools/cmd/staticcheck@v0.6.1 \
+    && go install golang.org/x/text/cmd/gotext@v0.22.0
+
+# Create bin directory for local sqlcmd builds
+RUN mkdir -p /home/vscode/bin && chown vscode:vscode /home/vscode/bin
+ENV PATH="/home/vscode/bin:${PATH}"

.devcontainer/README.md

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+# go-sqlcmd Development Container
+
+Dev Container / Codespaces environment with Go 1.24 and SQL Server 2025.
+
+## Quick Start
+
+**VS Code**: Open repo → click "Reopen in Container" when prompted.
+
+**Codespaces**: Click "Code" → "Codespaces" → "Create codespace".
+
+First build takes ~5 minutes.
+
+## Commands
+
+| Alias | What it does |
+|-------|--------------|
+| `gtest` | Run tests |
+| `ginstall` | Build and install sqlcmd to ~/bin |
+| `glint` | Run golangci-lint |
+| `sql` | Connect to SQL Server (go-sqlcmd) |
+| `sql-legacy` | Connect with legacy ODBC sqlcmd |
+| `test-db` | Test database connection |
+
+## SQL Server Connection
+
+- **Server**: `localhost,1433`
+- **User**: `sa`
+- **Password**: `$SQLCMDPASSWORD` env var (`SqlCmd@2025!` for local dev)
+- **Database**: `master` or `SqlCmdTest`
+
+Port 1433 is forwarded — connect from host tools (ADS, SSMS) using same credentials.
+
+## Two sqlcmd Versions
+
+- **go-sqlcmd**: `~/bin/sqlcmd` (default in PATH, use `sql` alias)
+- **Legacy ODBC**: `/opt/mssql-tools18/bin/sqlcmd` (use `sql-legacy` alias)
+
+## Customization
+
+**Change SQL version**: Edit `docker-compose.yml` image tag.
+
+**Add setup scripts**: Edit `.devcontainer/mssql/setup.sql`.
+
+**Change password**: Update `docker-compose.yml` and `devcontainer.json`.
+
+## Troubleshooting
+
+- **ARM64 (Apple Silicon)**: Use GitHub Codespaces instead - SQL Server has no native ARM64 images
+- **SQL Server not starting**: Check `docker logs $(docker ps -qf "name=db")`. Needs 2GB+ RAM
+- **Connection refused**: Wait ~30s for SQL Server to start
+- **sqlcmd not found**: Run `ginstall`

.devcontainer/devcontainer.json

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+{
+    "name": "go-sqlcmd Development",
+    "dockerComposeFile": "docker-compose.yml",
+    "service": "devcontainer",
+    "workspaceFolder": "/workspaces/go-sqlcmd",
+    "shutdownAction": "stopCompose",
+
+    // Configure tool-specific properties
+    "customizations": {
+        "vscode": {
+            "extensions": [
+                "golang.go",
+                "ms-mssql.mssql",
+                "ms-azuretools.vscode-docker",
+                "GitHub.copilot",
+                "GitHub.copilot-chat",
+                "eamodio.gitlens",
+                "EditorConfig.EditorConfig",
+                "streetsidesoftware.code-spell-checker"
+            ],
+            "settings": {
+                "go.toolsManagement.autoUpdate": false,
+                "go.useLanguageServer": true,
+                "go.lintTool": "golangci-lint",
+                "go.lintFlags": ["--fast"],
+                "go.testEnvVars": {
+                    "SQLCMDSERVER": "localhost",
+                    "SQLCMDUSER": "sa",
+                    "SQLCMDPASSWORD": "${env:SQLCMDPASSWORD}",
+                    "SQLCMDDATABASE": "master"
+                },
+                "mssql.connections": [
+                    {
+                        "server": "localhost,1433",
+                        "database": "master",
+                        "authenticationType": "SqlLogin",
+                        "user": "sa",
+                        "password": "",
+                        "savePassword": false,
+                        "profileName": "sqlcmd-container (use SQLCMDPASSWORD env var)",
+                        "encrypt": "Optional",
+                        "trustServerCertificate": true
+                    }
+                ],
+                "editor.formatOnSave": true,
+                "editor.defaultFormatter": "golang.go",
+                "[go]": {
+                    "editor.formatOnSave": true,
+                    "editor.codeActionsOnSave": {
+                        "source.organizeImports": "explicit"
+                    }
+                },
+                "terminal.integrated.defaultProfile.linux": "bash"
+            }
+        }
+    },
+
+    // Forward the SQL Server port
+    "forwardPorts": [1433],
+    "portsAttributes": {
+        "1433": {
+            "label": "SQL Server",
+            "onAutoForward": "silent"
+        }
+    },
+
+    // Use 'postCreateCommand' to run commands after the container is created
+    "postCreateCommand": "bash .devcontainer/post-create.sh",
+
+    // Environment variables for tests - password must match docker-compose.yml
+    // This is a development-only container credential, not a production secret.
+    // For GitHub Codespaces, you can override SQLCMDPASSWORD via Codespaces Secrets.
+    "remoteEnv": {
+        "SQLCMDSERVER": "localhost",
+        "SQLCMDUSER": "sa",
+        "SQLCMDPASSWORD": "${localEnv:SQLCMDPASSWORD:SqlCmd@2025!}",
+        "SQLCMDDATABASE": "master",
+        "SQLCMDDBNAME": "master"
+    },
+
+    // Features to add to the dev container
+    "features": {
+        "ghcr.io/devcontainers/features/docker-in-docker:2": {
+            "version": "latest",
+            "moby": true
+        },
+        "ghcr.io/devcontainers/features/github-cli:1": {
+            "version": "latest"
+        }
+    }
+}

.devcontainer/docker-compose.yml

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+version: '3.8'
+
+services:
+  devcontainer:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    volumes:
+      - ..:/workspaces/go-sqlcmd:cached
+    # Overrides default command so things don't shut down after the process ends.
+    command: sleep infinity
+    # Runs app on the same network as the database container, allows "forwardPorts" in devcontainer.json function.
+    network_mode: service:db
+    depends_on:
+      db:
+        condition: service_healthy
+
+  db:
+    image: mcr.microsoft.com/mssql/server:2025-latest
+    restart: unless-stopped
+    environment:
+      ACCEPT_EULA: "Y"
+      # Password can be overridden via SQLCMDPASSWORD environment variable
+      SA_PASSWORD: "${SQLCMDPASSWORD:-SqlCmd@2025!}"
+      MSSQL_SA_PASSWORD: "${SQLCMDPASSWORD:-SqlCmd@2025!}"
+      MSSQL_PID: "Developer"
+    volumes:
+      - mssql-data:/var/opt/mssql
+    healthcheck:
+      test: ["CMD-SHELL", "/opt/mssql-tools18/bin/sqlcmd -S localhost -U sa -P \"$$MSSQL_SA_PASSWORD\" -C -Q \"SELECT 1\" || exit 1"]
+      interval: 10s
+      timeout: 5s
+      retries: 15
+      start_period: 45s
+
+volumes:
+  mssql-data:

.devcontainer/mssql/setup.sql

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+-- go-sqlcmd Development Database Setup
+-- This script runs automatically when the devcontainer starts
+
+USE master;
+GO
+
+-- Create a test database for development
+IF NOT EXISTS (SELECT * FROM sys.databases WHERE name = 'SqlCmdTest')
+BEGIN
+    CREATE DATABASE SqlCmdTest;
+    PRINT 'Created database: SqlCmdTest';
+END
+GO
+
+-- Enable contained database authentication for testing
+-- Use TRY/CATCH in case this fails on certain SQL Server configurations
+BEGIN TRY
+    EXEC sp_configure 'contained database authentication', 1;
+    RECONFIGURE;
+END TRY
+BEGIN CATCH
+    PRINT 'Note: Could not enable contained database authentication (may already be enabled or not supported)';
+END CATCH;
+GO
+
+-- Make SqlCmdTest a contained database for testing
+BEGIN TRY
+    ALTER DATABASE SqlCmdTest SET CONTAINMENT = PARTIAL;
+END TRY
+BEGIN CATCH
+    PRINT 'Note: Could not set database containment (may not be supported)';
+END CATCH;
+GO
+
+USE SqlCmdTest;
+GO
+
+-- Create a sample table for quick testing
+IF NOT EXISTS (SELECT * FROM sys.tables WHERE name = 'TestTable')
+BEGIN
+    CREATE TABLE TestTable (
+        ID INT IDENTITY(1,1) PRIMARY KEY,
+        Name NVARCHAR(100) NOT NULL,
+        Value NVARCHAR(MAX),
+        CreatedAt DATETIME2 DEFAULT GETUTCDATE()
+    );
+
+    INSERT INTO TestTable (Name, Value) VALUES 
+        ('Test1', 'Sample value 1'),
+        ('Test2', 'Sample value 2'),
+        ('Test3', 'Sample value 3');
+
+    PRINT 'Created table: TestTable with sample data';
+END
+GO
+
+-- Create a view for testing
+IF NOT EXISTS (SELECT * FROM sys.views WHERE name = 'TestView')
+BEGIN
+    EXEC('CREATE VIEW TestView AS SELECT ID, Name, CreatedAt FROM TestTable');
+    PRINT 'Created view: TestView';
+END
+GO
+
+PRINT 'go-sqlcmd development database setup complete!';
+PRINT 'Test database: SqlCmdTest';
+PRINT 'Sample table: TestTable (3 rows)';
+PRINT 'Sample view: TestView';
+GO