Add CLI commands and template integration for build environment (#2742)

Add CLI commands and Dockerfile template integration for the build
environment configuration added in the previous PR.

CLI Commands:
- thv config set-build-env KEY value: Set a validated env variable
- thv config get-build-env [KEY]: Show one or all configured variables
- thv config unset-build-env KEY: Remove a specific variable
- thv config unset-build-env --all: Remove all variables

Template Integration:
- Add BuildEnv field to TemplateData struct
- Update npx.tmpl, uvx.tmpl, go.tmpl to inject ENV directives
- Modify protocol handler to load build env from config

Example usage:
  thv config set-build-env NPM_CONFIG_REGISTRY https://npm.corp.example.com
  thv config set-build-env GOPROXY https://goproxy.corp.example.com
  thv run npx://@modelcontextprotocol/server-github

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Signed-off-by: Juan Antonio Osorio <[email protected]>
Co-authored-by: Claude <[email protected]>

Author: JAORMX

cmd/thv/app/config_buildenv.go

@@ -0,0 +1,169 @@
+package app
+
+import (
+	"fmt"
+	"sort"
+
+	"github.com/spf13/cobra"
+
+	"github.com/stacklok/toolhive/pkg/config"
+)
+
+var (
+	unsetBuildEnvAll bool
+)
+
+var setBuildEnvCmd = &cobra.Command{
+	Use:   "set-build-env <KEY> <value>",
+	Short: "Set a build environment variable for protocol builds",
+	Long: `Set a build environment variable that will be injected into Dockerfiles
+during protocol builds (npx://, uvx://, go://). This is useful for configuring
+custom package mirrors in corporate environments.
+
+Environment variable names must:
+- Start with an uppercase letter
+- Contain only uppercase letters, numbers, and underscores
+- Not be a reserved system variable (PATH, HOME, etc.)
+
+Common use cases:
+- NPM_CONFIG_REGISTRY: Custom npm registry URL
+- PIP_INDEX_URL: Custom PyPI index URL
+- UV_DEFAULT_INDEX: Custom uv package index URL
+- GOPROXY: Custom Go module proxy URL
+- GOPRIVATE: Private Go module paths
+
+Examples:
+  thv config set-build-env NPM_CONFIG_REGISTRY https://npm.corp.example.com
+  thv config set-build-env PIP_INDEX_URL https://pypi.corp.example.com/simple
+  thv config set-build-env GOPROXY https://goproxy.corp.example.com
+  thv config set-build-env GOPRIVATE "github.com/myorg/*"`,
+	Args: cobra.ExactArgs(2),
+	RunE: setBuildEnvCmdFunc,
+}
+
+var getBuildEnvCmd = &cobra.Command{
+	Use:   "get-build-env [KEY]",
+	Short: "Get build environment variables",
+	Long: `Display configured build environment variables.
+If a KEY is provided, shows only that specific variable.
+If no KEY is provided, shows all configured variables.
+
+Examples:
+  thv config get-build-env                    # Show all variables
+  thv config get-build-env NPM_CONFIG_REGISTRY  # Show specific variable`,
+	Args: cobra.MaximumNArgs(1),
+	RunE: getBuildEnvCmdFunc,
+}
+
+var unsetBuildEnvCmd = &cobra.Command{
+	Use:   "unset-build-env [KEY]",
+	Short: "Remove build environment variable(s)",
+	Long: `Remove a specific build environment variable or all variables.
+
+Examples:
+  thv config unset-build-env NPM_CONFIG_REGISTRY  # Remove specific variable
+  thv config unset-build-env --all                # Remove all variables`,
+	Args: cobra.MaximumNArgs(1),
+	RunE: unsetBuildEnvCmdFunc,
+}
+
+func init() {
+	// Add build-env subcommands to config command
+	configCmd.AddCommand(setBuildEnvCmd)
+	configCmd.AddCommand(getBuildEnvCmd)
+	configCmd.AddCommand(unsetBuildEnvCmd)
+
+	// Add --all flag to unset command
+	unsetBuildEnvCmd.Flags().BoolVar(
+		&unsetBuildEnvAll,
+		"all",
+		false,
+		"Remove all build environment variables",
+	)
+}
+
+func setBuildEnvCmdFunc(_ *cobra.Command, args []string) error {
+	key := args[0]
+	value := args[1]
+
+	provider := config.NewDefaultProvider()
+	if err := provider.SetBuildEnv(key, value); err != nil {
+		return fmt.Errorf("failed to set build environment variable: %w", err)
+	}
+
+	fmt.Printf("Successfully set build environment variable: %s\n", key)
+	return nil
+}
+
+func getBuildEnvCmdFunc(_ *cobra.Command, args []string) error {
+	provider := config.NewDefaultProvider()
+
+	if len(args) == 1 {
+		// Get specific variable
+		key := args[0]
+		value, exists := provider.GetBuildEnv(key)
+		if !exists {
+			fmt.Printf("Build environment variable %s is not configured.\n", key)
+			return nil
+		}
+		fmt.Printf("%s=%s\n", key, value)
+		return nil
+	}
+
+	// Get all variables
+	envVars := provider.GetAllBuildEnv()
+	if len(envVars) == 0 {
+		fmt.Println("No build environment variables are configured.")
+		return nil
+	}
+
+	// Sort keys for consistent output
+	keys := make([]string, 0, len(envVars))
+	for k := range envVars {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	fmt.Println("Configured build environment variables:")
+	for _, k := range keys {
+		fmt.Printf("  %s=%s\n", k, envVars[k])
+	}
+	return nil
+}
+
+func unsetBuildEnvCmdFunc(_ *cobra.Command, args []string) error {
+	provider := config.NewDefaultProvider()
+
+	if unsetBuildEnvAll {
+		envVars := provider.GetAllBuildEnv()
+		if len(envVars) == 0 {
+			fmt.Println("No build environment variables are configured.")
+			return nil
+		}
+
+		if err := provider.UnsetAllBuildEnv(); err != nil {
+			return fmt.Errorf("failed to remove build environment variables: %w", err)
+		}
+
+		fmt.Printf("Successfully removed %d build environment variable(s).\n", len(envVars))
+		return nil
+	}
+
+	if len(args) == 0 {
+		return fmt.Errorf("please specify a KEY to remove or use --all to remove all variables")
+	}
+
+	key := args[0]
+	_, exists := provider.GetBuildEnv(key)
+	if !exists {
+		fmt.Printf("Build environment variable %s is not configured.\n", key)
+		return nil
+	}
+
+	if err := provider.UnsetBuildEnv(key); err != nil {
+		return fmt.Errorf("failed to remove build environment variable: %w", err)
+	}
+
+	fmt.Printf("Successfully removed build environment variable: %s\n", key)
+	return nil
+}

docs/cli/thv_config.md

@@ -1,5 +1,10 @@
 FROM golang:1.25-alpine AS builder
 
+{{if .BuildEnv}}
+# Custom build environment variables
+{{range $key, $value := .BuildEnv}}ENV {{$key}}="{{$value}}"
+{{end}}
+{{end}}
 {{if .CACertContent}}
 # Add custom CA certificate BEFORE any network operations
 # This ensures that package managers can verify TLS certificates in corporate networks

docs/cli/thv_config_get-build-env.md

@@ -1,5 +1,10 @@
 FROM node:22-alpine AS builder
 
+{{if .BuildEnv}}
+# Custom build environment variables
+{{range $key, $value := .BuildEnv}}ENV {{$key}}="{{$value}}"
+{{end}}
+{{end}}
 {{if .CACertContent}}
 # Add custom CA certificate BEFORE any network operations
 # This ensures that package managers can verify TLS certificates in corporate networks

docs/cli/thv_config_set-build-env.md

@@ -29,6 +29,10 @@ type TemplateData struct {
 	// These are typically required subcommands (e.g., "start") that must always be present.
 	// Runtime arguments passed via "-- <args>" will be appended after these build args.
 	BuildArgs []string
+	// BuildEnv contains environment variables to inject into the Dockerfile builder stage.
+	// These are used for configuring package managers (e.g., custom registry URLs).
+	// Keys must be uppercase with underscores, values are validated for safety.
+	BuildEnv map[string]string
 }
 
 // TransportType represents the type of transport to use.