feat: add stack state pull command

Downloads the current Terraform/OpenTofu state file for a stack
via the stateDownloadUrl GraphQL mutation and presigned S3 URL.

Usage: spacectl stack state pull [--id <stack-id>] [--output <file>]

Author: michalrom089

internal/cmd/stack/README.md

@@ -0,0 +1,30 @@
+# `spacectl stack state`
+
+`spacectl stack state` manages Terraform/OpenTofu state files for Spacelift stacks.
+
+## `pull`
+
+Downloads the current state file for a stack.
+
+```bash
+# Output to stdout
+spacectl stack state pull --id my-stack
+
+# Save to file
+spacectl stack state pull --id my-stack -o terraform.tfstate
+
+# Auto-detect stack from current directory
+spacectl stack state pull
+
+# Pretty-print
+spacectl stack state pull --id my-stack | jq .
+```
+
+### Prerequisites
+
+The stack must have:
+
+- **Manages state** enabled (Spacelift manages the Terraform state)
+- **External state access** enabled (stack setting)
+
+The user must have **State download** permission or Space admin role.

internal/cmd/stack/stack.go

@@ -769,6 +769,36 @@ func Command() cmd.Command {
 					},
 				},
 			},
+			{
+				Name:  "state",
+				Usage: "Manage stack state",
+				Versions: []cmd.VersionedCommand{
+					{
+						EarliestVersion: cmd.SupportedVersionAll,
+						Command:         &cli.Command{},
+					},
+				},
+				Subcommands: []cmd.Command{
+					{
+						Name:  "pull",
+						Usage: "Download the current state file for a stack",
+						Versions: []cmd.VersionedCommand{
+							{
+								EarliestVersion: cmd.SupportedVersionAll,
+								Command: &cli.Command{
+									Flags: []cli.Flag{
+										flagStackID,
+										flagOutputFile,
+									},
+									Action:    statePull(),
+									Before:    authenticated.Ensure,
+									ArgsUsage: cmd.EmptyArgsUsage,
+								},
+							},
+						},
+					},
+				},
+			},
 			{
 				Name:  "resources",
 				Usage: "Manage and view resources for stacks",

internal/cmd/stack/state.go

@@ -0,0 +1,90 @@
+package stack
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+
+	"github.com/shurcooL/graphql"
+	"github.com/urfave/cli/v3"
+
+	"github.com/spacelift-io/spacectl/internal/cmd/authenticated"
+)
+
+var flagOutputFile = &cli.StringFlag{
+	Name:    "output",
+	Aliases: []string{"o"},
+	Usage:   "[Optional] `PATH` to write the state file to (defaults to stdout)",
+}
+
+func statePull() cli.ActionFunc {
+	return func(ctx context.Context, cliCmd *cli.Command) error {
+		stackID, err := getStackID(ctx, cliCmd)
+		if err != nil {
+			return err
+		}
+
+		var mutation struct {
+			StateDownloadURL struct {
+				URL string `graphql:"url"`
+			} `graphql:"stateDownloadUrl(input: $input)"`
+		}
+
+		variables := map[string]any{
+			"input": StateDownloadUrlInput{StackID: graphql.ID(stackID)},
+		}
+
+		if err := authenticated.Client().Mutate(ctx, &mutation, variables); err != nil {
+			return fmt.Errorf("failed to get state download URL for stack %q: %w", stackID, err)
+		}
+
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, mutation.StateDownloadURL.URL, nil)
+		if err != nil {
+			return fmt.Errorf("failed to create download request: %w", err)
+		}
+
+		resp, err := http.DefaultClient.Do(req)
+		if err != nil {
+			return fmt.Errorf("failed to download state: %w", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusOK {
+			body, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
+			return fmt.Errorf("failed to download state: HTTP %d: %s", resp.StatusCode, string(body))
+		}
+
+		outputPath := cliCmd.String(flagOutputFile.Name)
+		if outputPath == "" {
+			if _, err := io.Copy(os.Stdout, resp.Body); err != nil {
+				return fmt.Errorf("failed to write state: %w", err)
+			}
+			return nil
+		}
+
+		f, err := os.OpenFile(filepath.Clean(outputPath), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
+		if err != nil {
+			return fmt.Errorf("failed to create output file: %w", err)
+		}
+
+		if _, err := io.Copy(f, resp.Body); err != nil {
+			f.Close()
+			os.Remove(filepath.Clean(outputPath))
+			return fmt.Errorf("failed to write state: %w", err)
+		}
+
+		if err := f.Close(); err != nil {
+			os.Remove(filepath.Clean(outputPath))
+			return fmt.Errorf("failed to flush state file: %w", err)
+		}
+
+		return nil
+	}
+}
+
+type StateDownloadUrlInput struct { //nolint:staticcheck // type name must match GraphQL schema exactly
+	StackID graphql.ID `json:"stackId"`
+}