migrate to OpenTofu with Terraform fallback

Add binary lookup in both terraform.go and destroy.go:
tofu preferred, terraform fallback. Update all docs to
reflect the OpenTofu-first approach.

DETAILS.md

@@ -53,7 +53,7 @@ obm/
 │   │   │   └── hetzner_test.go
 │   │   └── provider_test.go
 │   ├── terraform/
-│   │   └── terraform.go           # Runner: Init, Plan, Apply, Destroy wrappers
+│   │   └── terraform.go           # Runner: Init, Plan, Apply, Destroy (OpenTofu/Terraform)
 │   └── validation/
 │       ├── validation.go          # Check interface, Runner, CheckResult, Status enum
 │       └── validation_test.go
@@ -82,7 +82,7 @@ obm/
 | `obm deploy` | `--config <path>` | Interactive walkthrough (default) or non-interactive from YAML |
 | `obm validate` | `--env-file <path>` | Load `.env`, check required vars, validate API keys |
 | `obm status` | — | Show deployment state (not yet implemented) |
-| `obm destroy` | — | Confirmation prompt → `terraform destroy` → state cleanup |
+| `obm destroy` | — | Confirmation prompt → `tofu destroy` → state cleanup |
 | `obm version` | — | Print version with commit hash and build time |
 | `obm help` | — | Print usage |
 
@@ -111,7 +111,7 @@ The `obm deploy` interactive flow runs 8 steps in sequence:
 7. **Tailscale** — Optional VPN setup. Auth key and tailnet domain.
 8. **Discord** — Optional bot integration. Bot token, server ID, user IDs.
 
-Final step: summary display with cost estimate → confirm → write `.env` → optionally run `terraform init && terraform apply`.
+Final step: summary display with cost estimate → confirm → write `.env` → optionally run `tofu init && tofu apply` (or `terraform` if installed).
 
 ### Framework-specific defaults
 
@@ -355,15 +355,15 @@ DigitalOcean prices:
 
 ---
 
-## Terraform Integration
+## Terraform / OpenTofu Integration
 
-`obm` generates the `.env` file that Terraform expects. The actual Terraform configs live in the separate [openboatmobile-ai](https://github.com/openboatmobile/openboatmobile-ai) repo.
+`obm` generates the `.env` file that OpenTofu (or Terraform) expects. The actual infrastructure configs live in the separate [openboatmobile-ai](https://github.com/openboatmobile/openboatmobile-ai) repo.
 
-The `internal/terraform/terraform.go` wrapper provides:
-- `Runner.Init()` — `terraform init -input=false`
-- `Runner.Plan(destroy bool)` — `terraform plan` (with optional `-destroy` flag)
-- `Runner.Apply()` — `terraform apply -auto-approve`
-- `Runner.Destroy()` — `terraform destroy -auto-approve`
+The `internal/terraform/terraform.go` wrapper provides (auto-detects OpenTofu first, Terraform fallback):
+- `Runner.Init()` — `tofu init -input=false`
+- `Runner.Plan(destroy bool)` — `tofu plan` (with optional `-destroy` flag)
+- `Runner.Apply()` — `tofu apply -auto-approve`
+- `Runner.Destroy()` — `tofu destroy -auto-approve`
 
 All commands run in the `WorkDir` and capture combined output.
 
@@ -391,7 +391,7 @@ User sets `TF_VAR_*` env vars → sourced from `.env` → Terraform reads them
 
 ## Destroy Flow
 
-`obm destroy` reads `terraform.tfstate` to list resources, shows them, asks for confirmation, runs `terraform destroy`, then cleans up state files unless `--keep-state` is set.
+`obm destroy` reads `terraform.tfstate` to list resources, shows them, asks for confirmation, runs `tofu destroy`, then cleans up state files unless `--keep-state` is set.
 
 ---
 

LLMs.md

@@ -85,7 +85,7 @@ When your human runs `obm deploy`, they'll go through these in order:
 7. **Tailscale** — Optional VPN (auth key + tailnet)
 8. **Discord** — Optional bot integration (token, server ID, user IDs)
 
-After all 8 steps: summary + cost estimate → confirm → `.env` written → optional `terraform init && apply`.
+After all 8 steps: summary + cost estimate → confirm → `.env` written → optional `tofu init && tofu apply` (or `terraform` if installed).
 
 ---
 
@@ -200,7 +200,7 @@ This loads `.env`, checks required variables, and validates inference API keys a
 obm destroy
 ```
 
-It asks for confirmation. It reads `terraform.tfstate` to show what will be destroyed.
+It asks for confirmation. It reads the state file (`terraform.tfstate`) to show what will be destroyed.
 
 ### "Set up CI/CD deployment"
 

README.md

@@ -115,9 +115,9 @@ The AI model API costs are separate, and depend on your usage. Generally that's
 
 ## What happens under the hood?
 
-`obm` generates a `.env` file that [Terraform](https://terraform.io) reads to provision your server, install the agent software, and configure everything. You don't need to know Terraform — `obm` handles it.
+`obm` generates a `.env` file that [OpenTofu](https://opentofu.org) (or [Terraform](https://terraform.io) as a fallback) reads to provision your server, install the agent software, and configure everything. You don't need to know either — `obm` handles it.
 
-The Terraform configs live in the [openboatmobile-ai](https://github.com/openboatmobile/openboatmobile-ai) repo. `obm` is the friendly CLI wrapper around them.
+The infrastructure configs live in the [openboatmobile-ai](https://github.com/openboatmobile/openboatmobile-ai) repo. `obm` is the friendly CLI wrapper around them.
 
 ---
 

internal/destroy/destroy.go

@@ -12,6 +12,16 @@ import (
 	"github.com/openboatmobile/obm/internal/prompt"
 )
 
+// tfBinary returns the path to the IaC binary: tofu preferred, terraform fallback.
+func tfBinary() string {
+	for _, name := range []string{"tofu", "terraform"} {
+		if path, err := exec.LookPath(name); err == nil {
+			return path
+		}
+	}
+	return "tofu"
+}
+
 // Options configures the destroy operation.
 type Options struct {
 	WorkDir     string   // Working directory (default: current)
@@ -198,7 +208,7 @@ func displayDestroyPlan(resources []Resource) {
 	fmt.Println()
 }
 
-// runTerraformDestroy executes terraform destroy.
+// runTerraformDestroy executes tofu/terraform destroy.
 func runTerraformDestroy(workDir string, opts *Options) error {
 	args := []string{"destroy", "-auto-approve"}
 
@@ -207,7 +217,7 @@ func runTerraformDestroy(workDir string, opts *Options) error {
 		args = append(args, "-var-file", vf)
 	}
 
-	cmd := exec.Command("terraform", args...)
+	cmd := exec.Command(tfBinary(), args...)
 	cmd.Dir = workDir
 
 	// Stream output to stdout/stderr

internal/terraform/terraform.go

@@ -1,4 +1,5 @@
-// Package terraform wraps Terraform operations (init, plan, apply, destroy).
+// Package terraform wraps IaC operations (init, plan, apply, destroy).
+// Supports OpenTofu (preferred) and Terraform (fallback).
 package terraform
 
 import (
@@ -6,22 +7,32 @@ import (
 	"os/exec"
 )
 
-// Runner executes Terraform commands.
+// binary returns the path to the IaC binary: tofu preferred, terraform fallback.
+func binary() string {
+	for _, name := range []string{"tofu", "terraform"} {
+		if path, err := exec.LookPath(name); err == nil {
+			return path
+		}
+	}
+	return "tofu" // fallback — will produce a useful error at runtime
+}
+
+// Runner executes infrastructure-as-code commands.
 type Runner struct {
 	WorkDir string
 }
 
-// NewRunner creates a Terraform runner for the given working directory.
+// NewRunner creates a runner for the given working directory.
 func NewRunner(workDir string) *Runner {
 	return &Runner{WorkDir: workDir}
 }
 
-// Init runs terraform init.
+// Init runs init.
 func (r *Runner) Init() error {
 	return r.run("init", "-input=false")
 }
 
-// Plan runs terraform plan.
+// Plan runs plan.
 func (r *Runner) Plan(destroy bool) error {
 	args := []string{"plan"}
 	if destroy {
@@ -30,22 +41,23 @@ func (r *Runner) Plan(destroy bool) error {
 	return r.run(args...)
 }
 
-// Apply runs terraform apply.
+// Apply runs apply.
 func (r *Runner) Apply() error {
 	return r.run("apply", "-auto-approve")
 }
 
-// Destroy runs terraform destroy.
+// Destroy runs destroy.
 func (r *Runner) Destroy() error {
 	return r.run("destroy", "-auto-approve")
 }
 
 func (r *Runner) run(args ...string) error {
-	cmd := exec.Command("terraform", args...)
+	bin := binary()
+	cmd := exec.Command(bin, args...)
 	cmd.Dir = r.WorkDir
 	output, err := cmd.CombinedOutput()
 	if err != nil {
-		return fmt.Errorf("terraform %v: %w\n%s", args, err, output)
+		return fmt.Errorf("%s %v: %w\n%s", bin, args, err, output)
 	}
 	return nil
 }