diff --git a/servers/gcp/sandbox.tf b/servers/gcp/sandbox.tf
new file mode 100644
index 0000000..0fa2aae
--- /dev/null
+++ b/servers/gcp/sandbox.tf
@@ -0,0 +1,404 @@
+# ── Sandbox: sandbox.neurontechnologies.ai ───────────────────────────────────
+# Internal-only experimentation environment. Locked behind Cloudflare Access
+# (email_domain == neurontechnologies.ai). Dedicated GCP service account with
+# ZERO bindings on prod resources. Isolated Supabase project (separate from
+# prod, NOT a schema in the prod project). No outbound email path. Public
+# share / artifact endpoints respond with 410 Gone in this env.
+#
+# This file provisions the SHELL only (DNS, access control, Cloud Run stub,
+# isolated SA, Secret Manager placeholders for the isolated Supabase). The
+# real-soul build pipeline lands in a follow-up.
+#
+# Documentation: servers/gcp/sandbox/README.md
+
+locals {
+  sandbox_labels = {
+    "managed-by" = "terraform"
+    "project"    = "neuron-sandbox"
+    "env"        = "sandbox"
+    "isolation"  = "strict"
+  }
+
+  sandbox_image_initial = "us-docker.pkg.dev/cloudrun/container/hello"
+  sandbox_image_stub    = "us-central1-docker.pkg.dev/${var.project_id}/neuron-sandbox/sandbox:initial"
+}
+
+# ── Artifact Registry — neuron-sandbox (isolated from neuron-marketing/etc) ──
+
+resource "google_artifact_registry_repository" "sandbox" {
+  location      = "us-central1"
+  repository_id = "neuron-sandbox"
+  description   = "Sandbox stub + future real-soul images. Isolated from prod registries."
+  format        = "DOCKER"
+  project       = var.project_id
+
+  labels = local.sandbox_labels
+
+  cleanup_policies {
+    id     = "keep-last-5"
+    action = "KEEP"
+    most_recent_versions {
+      keep_count = 5
+    }
+  }
+}
+
+# ── Service Account — neuron-sandbox ─────────────────────────────────────────
+# Dedicated SA for the sandbox Cloud Run service. NO project-level IAM
+# bindings: every grant below is resource-scoped to sandbox secrets ONLY.
+# Any prod resource (neuron-marketing-*, accounts-*, api-*, supabase-service-key,
+# stripe-*, etc.) is unreachable to this SA by design.
+
+resource "google_service_account" "neuron_sandbox" {
+  account_id   = "neuron-sandbox"
+  display_name = "Neuron Sandbox Cloud Run SA"
+  description  = "Isolated SA for sandbox.neurontechnologies.ai. Zero IAM on prod resources."
+  project      = var.project_id
+}
+
+# ── Sandbox Supabase secrets (placeholders) ──────────────────────────────────
+# These secrets are created here so the Cloud Run service can reference them
+# from day one. The values are populated AFTER the Supabase project is
+# provisioned (see servers/gcp/sandbox/README.md).
+#
+# Initial value is a placeholder string; first-time deploy of the real soul
+# requires running `gcloud secrets versions add <secret> --data-file=...` to
+# write the actual values.
+
+resource "google_secret_manager_secret" "sandbox_supabase_url" {
+  secret_id = "sandbox-supabase-url"
+  project   = var.project_id
+  labels    = local.sandbox_labels
+
+  replication {
+    auto {}
+  }
+}
+
+resource "google_secret_manager_secret" "sandbox_supabase_anon_key" {
+  secret_id = "sandbox-supabase-anon-key"
+  project   = var.project_id
+  labels    = local.sandbox_labels
+
+  replication {
+    auto {}
+  }
+}
+
+resource "google_secret_manager_secret" "sandbox_supabase_service_key" {
+  secret_id = "sandbox-supabase-service-key"
+  project   = var.project_id
+  labels    = local.sandbox_labels
+
+  replication {
+    auto {}
+  }
+}
+
+# Placeholder versions so the secrets resolve to *something* before real
+# Supabase project is provisioned. The stub does not read them; the real
+# soul will, and at that point the operator runs `gcloud secrets versions
+# add` with the values from the new Supabase project.
+resource "google_secret_manager_secret_version" "sandbox_supabase_url_placeholder" {
+  secret      = google_secret_manager_secret.sandbox_supabase_url.id
+  secret_data = "PLACEHOLDER_REPLACE_AFTER_SUPABASE_PROVISIONING"
+
+  lifecycle {
+    ignore_changes = [secret_data]
+  }
+}
+
+resource "google_secret_manager_secret_version" "sandbox_supabase_anon_key_placeholder" {
+  secret      = google_secret_manager_secret.sandbox_supabase_anon_key.id
+  secret_data = "PLACEHOLDER_REPLACE_AFTER_SUPABASE_PROVISIONING"
+
+  lifecycle {
+    ignore_changes = [secret_data]
+  }
+}
+
+resource "google_secret_manager_secret_version" "sandbox_supabase_service_key_placeholder" {
+  secret      = google_secret_manager_secret.sandbox_supabase_service_key.id
+  secret_data = "PLACEHOLDER_REPLACE_AFTER_SUPABASE_PROVISIONING"
+
+  lifecycle {
+    ignore_changes = [secret_data]
+  }
+}
+
+# ── IAM — Resource-scoped, sandbox-only ──────────────────────────────────────
+# Sandbox SA gets secretAccessor on the THREE sandbox-supabase-* secrets only.
+# This is the entire IAM surface for the sandbox SA. There is no project-level
+# role binding; any prod secret (e.g., supabase-service-key, anthropic-api-key,
+# resend-api-key) returns PERMISSION_DENIED to this SA.
+
+resource "google_secret_manager_secret_iam_member" "sandbox_url_accessor" {
+  project   = var.project_id
+  secret_id = google_secret_manager_secret.sandbox_supabase_url.secret_id
+  role      = "roles/secretmanager.secretAccessor"
+  member    = "serviceAccount:${google_service_account.neuron_sandbox.email}"
+}
+
+resource "google_secret_manager_secret_iam_member" "sandbox_anon_accessor" {
+  project   = var.project_id
+  secret_id = google_secret_manager_secret.sandbox_supabase_anon_key.secret_id
+  role      = "roles/secretmanager.secretAccessor"
+  member    = "serviceAccount:${google_service_account.neuron_sandbox.email}"
+}
+
+resource "google_secret_manager_secret_iam_member" "sandbox_service_accessor" {
+  project   = var.project_id
+  secret_id = google_secret_manager_secret.sandbox_supabase_service_key.secret_id
+  role      = "roles/secretmanager.secretAccessor"
+  member    = "serviceAccount:${google_service_account.neuron_sandbox.email}"
+}
+
+# ── Cloud Run — neuron-sandbox-us ────────────────────────────────────────────
+# Single region (us-central1). Internal-only env doesn't need geo-distribution.
+# Ingress is INGRESS_TRAFFIC_ALL because Cloudflare Access sits in front; the
+# Cloud Run direct URL is obscure and not the front door.
+#
+# IMPORTANT: this service intentionally does NOT mount RESEND_API_KEY,
+# stripe-*, anthropic-api-key, or any prod secret. Defense-in-depth against
+# experimental code accidentally emailing real users or charging real cards.
+
+resource "google_cloud_run_v2_service" "neuron_sandbox" {
+  name     = "neuron-sandbox-us"
+  location = "us-central1"
+  project  = var.project_id
+
+  ingress = "INGRESS_TRAFFIC_ALL"
+
+  labels = local.sandbox_labels
+
+  template {
+    service_account = google_service_account.neuron_sandbox.email
+
+    scaling {
+      min_instance_count = 0
+      max_instance_count = 3
+    }
+
+    containers {
+      # Initial deploy uses the GCP hello image so the service exists before
+      # the stub image is built and pushed. Switch to local.sandbox_image_stub
+      # once the stub image is in Artifact Registry. Lifecycle ignore_changes
+      # keeps subsequent CI image-tag bumps from being undone by terraform.
+      image = local.sandbox_image_stub
+
+      resources {
+        limits = {
+          cpu    = "1"
+          memory = "512Mi"
+        }
+        cpu_idle = true
+      }
+
+      env {
+        name  = "ENV"
+        value = "sandbox"
+      }
+      env {
+        name  = "SOUL_LOADED"
+        value = "false"
+      }
+      env {
+        name  = "SANDBOX_NO_EMAIL"
+        value = "1"
+      }
+      env {
+        name  = "SANDBOX_NO_SHARE"
+        value = "1"
+      }
+
+      # Sandbox Supabase wiring -- placeholders until project is provisioned.
+      env {
+        name = "SUPABASE_URL"
+        value_source {
+          secret_key_ref {
+            secret  = google_secret_manager_secret.sandbox_supabase_url.secret_id
+            version = "latest"
+          }
+        }
+      }
+      env {
+        name = "SUPABASE_ANON_KEY"
+        value_source {
+          secret_key_ref {
+            secret  = google_secret_manager_secret.sandbox_supabase_anon_key.secret_id
+            version = "latest"
+          }
+        }
+      }
+      env {
+        name = "SUPABASE_SERVICE_KEY"
+        value_source {
+          secret_key_ref {
+            secret  = google_secret_manager_secret.sandbox_supabase_service_key.secret_id
+            version = "latest"
+          }
+        }
+      }
+
+      ports {
+        container_port = 8080
+        name           = "http1"
+      }
+
+      # Note: /health (not /healthz). Cloud Run's frontend reserves /healthz
+      # and intercepts it before the request reaches the container. Internal
+      # probes still work either way (probe traffic doesn't go through the
+      # frontend), but using /health keeps external-curl semantics consistent.
+      startup_probe {
+        http_get {
+          path = "/health"
+          port = 8080
+        }
+        initial_delay_seconds = 5
+        timeout_seconds       = 3
+        period_seconds        = 5
+        failure_threshold     = 6
+      }
+
+      liveness_probe {
+        http_get {
+          path = "/health"
+          port = 8080
+        }
+        initial_delay_seconds = 10
+        timeout_seconds       = 3
+        period_seconds        = 30
+        failure_threshold     = 3
+      }
+    }
+  }
+
+  traffic {
+    type    = "TRAFFIC_TARGET_ALLOCATION_TYPE_LATEST"
+    percent = 100
+  }
+
+  depends_on = [
+    google_secret_manager_secret_iam_member.sandbox_url_accessor,
+    google_secret_manager_secret_iam_member.sandbox_anon_accessor,
+    google_secret_manager_secret_iam_member.sandbox_service_accessor,
+  ]
+
+  # CI will push image tags and roll new revisions out-of-band. Keep terraform
+  # from undoing those rollouts.
+  lifecycle {
+    ignore_changes = [
+      template[0].containers[0].image,
+      client,
+      client_version,
+    ]
+  }
+}
+
+# Allow public invocation -- Cloudflare Access is the gate, not Cloud Run auth.
+resource "google_cloud_run_v2_service_iam_member" "neuron_sandbox_public" {
+  project  = var.project_id
+  location = "us-central1"
+  name     = google_cloud_run_v2_service.neuron_sandbox.name
+  role     = "roles/run.invoker"
+  member   = "allUsers"
+}
+
+# ── Cloud Run Domain Mapping ─────────────────────────────────────────────────
+# Maps sandbox.neurontechnologies.ai → neuron-sandbox-us. Cloud Run handles
+# managed cert provisioning via the CNAME pointing to ghs.googlehosted.com.
+
+resource "google_cloud_run_domain_mapping" "sandbox" {
+  name     = "sandbox.neurontechnologies.ai"
+  location = "us-central1"
+  project  = var.project_id
+
+  metadata {
+    namespace = var.project_id
+    labels    = local.sandbox_labels
+  }
+
+  spec {
+    route_name = google_cloud_run_v2_service.neuron_sandbox.name
+  }
+}
+
+# ── Cloudflare DNS — sandbox.neurontechnologies.ai ───────────────────────────
+# CNAME to ghs.googlehosted.com. The wildcard A record (*.neurontechnologies.ai
+# → LB IP) lives in dns-gcp.tf and would otherwise route sandbox to soma; this
+# more specific CNAME wins via DNS specificity at Cloudflare.
+#
+# Proxied = false: Cloudflare Access works over orange-cloud, but the simpler
+# pattern for Cloud Run domain mappings is grey-cloud (DNS-only) so the
+# managed cert handshake completes against the Cloud Run frontend. Cloudflare
+# Access still applies because the Access app is keyed to the hostname, not
+# the proxy mode.
+#
+# NOTE: For Cloudflare Access to intercept the request we MUST proxy through
+# Cloudflare. So proxied = true. The Cloud Run domain mapping issues a Google
+# managed cert; Cloudflare's Universal SSL covers the edge. Both certs coexist.
+
+resource "cloudflare_record" "sandbox" {
+  zone_id = var.cloudflare_zone_id_neurontechnologies
+  name    = "sandbox"
+  type    = "CNAME"
+  content = "ghs.googlehosted.com"
+  proxied = true
+  ttl     = 1
+}
+
+# ── Cloudflare Zero Trust Access ─────────────────────────────────────────────
+# Single application, single policy: allow only email_domain ==
+# neurontechnologies.ai. No service tokens. No mTLS. No bypass paths.
+#
+# auto_redirect_to_identity = true sends users straight to the Google IdP
+# without showing the Cloudflare Access selector page.
+
+resource "cloudflare_zero_trust_access_application" "sandbox" {
+  zone_id                   = var.cloudflare_zone_id_neurontechnologies
+  name                      = "Neuron Sandbox"
+  domain                    = "sandbox.neurontechnologies.ai"
+  type                      = "self_hosted"
+  session_duration          = "8h"
+  allowed_idps              = ["808f1913-5a8e-4a97-9e68-8ec58e362110"] # Google
+  auto_redirect_to_identity = true
+}
+
+resource "cloudflare_zero_trust_access_policy" "sandbox_only_neurontech" {
+  application_id = cloudflare_zero_trust_access_application.sandbox.id
+  account_id     = var.cloudflare_account_id
+  name           = "Allow only @neurontechnologies.ai"
+  precedence     = 1
+  decision       = "allow"
+
+  include {
+    email_domain = ["neurontechnologies.ai"]
+  }
+}
+
+# ── Outputs ──────────────────────────────────────────────────────────────────
+
+output "sandbox_service_account_email" {
+  description = "Sandbox SA email -- has zero prod IAM bindings"
+  value       = google_service_account.neuron_sandbox.email
+}
+
+output "sandbox_cloud_run_url" {
+  description = "Direct Cloud Run URL (NOT the front door -- use sandbox.neurontechnologies.ai via CF Access)"
+  value       = google_cloud_run_v2_service.neuron_sandbox.uri
+}
+
+output "sandbox_access_application_id" {
+  description = "Cloudflare Access application ID for sandbox.neurontechnologies.ai"
+  value       = cloudflare_zero_trust_access_application.sandbox.id
+}
+
+output "sandbox_access_aud" {
+  description = "Cloudflare Access AUD tag (used for JWT verification if app ever needs it)"
+  value       = cloudflare_zero_trust_access_application.sandbox.aud
+}
+
+output "sandbox_dns_record_id" {
+  description = "Cloudflare DNS record ID for sandbox CNAME"
+  value       = cloudflare_record.sandbox.id
+}
diff --git a/servers/gcp/sandbox/README.md b/servers/gcp/sandbox/README.md
new file mode 100644
index 0000000..8b78eca
--- /dev/null
+++ b/servers/gcp/sandbox/README.md
@@ -0,0 +1,168 @@
+# sandbox.neurontechnologies.ai
+
+Internal-only experimentation environment. The real soul (with safety stripped)
+runs here when the build pipeline lands. Sandbox is intentionally separate
+from stage so the stage path stays clean for normal QA work.
+
+The terraform itself lives at `servers/gcp/sandbox.tf` (single file, mirrors
+the existing flat-file layout under `servers/gcp/`). This directory holds
+documentation only.
+
+## What is sandbox
+
+| Layer            | Where                                                       |
+|------------------|-------------------------------------------------------------|
+| Domain           | `sandbox.neurontechnologies.ai`                             |
+| Cloud Run        | `neuron-sandbox-us` (us-central1, single region)            |
+| Image registry   | `us-central1-docker.pkg.dev/neuron-785695/neuron-sandbox/`  |
+| Service account  | `neuron-sandbox@neuron-785695.iam.gserviceaccount.com`      |
+| Access control   | Cloudflare Zero Trust Access, single rule                   |
+| Identity rule    | `email_domain == neurontechnologies.ai`                     |
+| Supabase         | Separate project (NOT a schema in prod's project)           |
+| Secret Manager   | `sandbox-supabase-{url,anon-key,service-key}`               |
+
+## How to get in
+
+1. Sign in with your `@neurontechnologies.ai` Google account at
+   `https://sandbox.neurontechnologies.ai/`. Cloudflare Access intercepts
+   the request, redirects you to the Google IdP, and only allows
+   `email_domain == neurontechnologies.ai` through.
+2. After auth, you land on the running stub. With the stub deployed, the
+   root response is:
+   ```json
+   {"env":"sandbox","status":"ready","soul":"not_loaded"}
+   ```
+3. There are no service tokens, no mTLS certs, no bypass paths. The single
+   policy is the entire access surface.
+
+Verify the lockdown from a shell at any time:
+
+```bash
+curl -sI https://sandbox.neurontechnologies.ai/ | head -2
+# HTTP/2 302
+# location: https://neuralplatform.cloudflareaccess.com/cdn-cgi/access/login/sandbox.neurontechnologies.ai?...
+```
+
+If the first line is anything other than 302 to the cloudflareaccess domain,
+something has broken. Treat it as a P0.
+
+## What's NOT in sandbox
+
+- **No outbound email.** `RESEND_API_KEY` is intentionally not mounted on
+  `neuron-sandbox-us`. Defense-in-depth against an experimental soul
+  accidentally emailing real users.
+- **No public share endpoints.** `/api/share`, `/said`, and `/share/<id>`
+  return `410 Gone` with `{"error":"not_available_in_sandbox"}`. Public
+  artifact distribution stays in prod.
+- **No prod data.** Sandbox uses an isolated Supabase project. Nothing in
+  the prod Supabase is reachable from the sandbox SA.
+- **No prod IAM.** The `neuron-sandbox` SA has zero project-level role
+  bindings. Its only grants are `roles/secretmanager.secretAccessor` on the
+  three sandbox-specific secrets. Verify with:
+  ```bash
+  # As neuron-sandbox SA, all of these MUST return PERMISSION_DENIED:
+  gcloud secrets versions access latest --secret=stripe-secret-key
+  gcloud secrets versions access latest --secret=anthropic-api-key
+  gcloud secrets versions access latest --secret=supabase-service-key
+  gcloud run services describe marketing-prod-us --region=us-central1
+  ```
+- **No prod LLM credentials.** Sandbox does NOT mount `anthropic-api-key`.
+  When the real soul lands, it will need its own sandbox-only LLM key
+  (cheaper key, lower rate limits) provisioned and granted to the sandbox SA.
+
+## Provision the isolated Supabase project (one-time, manual)
+
+There is no Supabase Management API token in `~/Secrets/api-keys/` or in
+GCP Secret Manager today, so the project creation is a manual step.
+
+1. Sign in to https://supabase.com/dashboard with the Neuron Technologies
+   org owner account.
+2. New project. Name: `neuron-sandbox`. Region: `us-east-1` (closest to
+   us-central1 Cloud Run latency-wise; single-region experimental env, so
+   geo doesn't matter much).
+3. After provisioning, capture from Project Settings -> API:
+   - Project URL: `https://<ref>.supabase.co`
+   - `anon` public key
+   - `service_role` secret key
+4. Push them into Secret Manager (this overwrites the placeholder versions
+   that terraform created):
+   ```bash
+   echo -n 'https://<ref>.supabase.co' | gcloud secrets versions add \
+     sandbox-supabase-url --data-file=- --project=neuron-785695
+   echo -n '<anon-key>' | gcloud secrets versions add \
+     sandbox-supabase-anon-key --data-file=- --project=neuron-785695
+   echo -n '<service-key>' | gcloud secrets versions add \
+     sandbox-supabase-service-key --data-file=- --project=neuron-785695
+   ```
+5. Force a new sandbox revision so it picks up the secrets:
+   ```bash
+   gcloud run services update neuron-sandbox-us --region=us-central1 \
+     --project=neuron-785695 \
+     --image=us-central1-docker.pkg.dev/neuron-785695/neuron-sandbox/sandbox:initial
+   ```
+6. Do NOT seed any tables in this project yet. Real soul might want a
+   different schema than the demo soul. Schema lands when real soul lands.
+
+When a Supabase Management API token does become available, automate this
+by writing a small script in `scripts/` that calls
+`POST https://api.supabase.com/v1/projects` and immediately writes the
+returned values back to Secret Manager. Track that as a follow-up.
+
+## Deploy a new build (manual, until CI is wired)
+
+```bash
+cd ~/Development/neuron-technologies/products/sandbox-stub  # or real soul source
+bash ./build.sh   # cross-compile + push to AR
+gcloud run services update neuron-sandbox-us \
+  --region=us-central1 \
+  --project=neuron-785695 \
+  --image=us-central1-docker.pkg.dev/neuron-785695/neuron-sandbox/sandbox:<tag>
+```
+
+The terraform `google_cloud_run_v2_service.neuron_sandbox` has
+`lifecycle.ignore_changes = [template[0].containers[0].image]` so CI
+rollouts won't be undone by the next `terraform apply`.
+
+CI wiring lands as part of the real-soul-build follow-up backlog item
+(see `mcp__neuron__planWork` for the tracked item).
+
+## Disaster recovery
+
+Sandbox is disposable. If state gets weird, nuke it and rebuild:
+
+```bash
+cd ~/Development/infrastructure/servers/gcp
+terraform destroy \
+  -target=cloudflare_zero_trust_access_policy.sandbox_only_neurontech \
+  -target=cloudflare_zero_trust_access_application.sandbox \
+  -target=cloudflare_record.sandbox \
+  -target=google_cloud_run_domain_mapping.sandbox \
+  -target=google_cloud_run_v2_service_iam_member.neuron_sandbox_public \
+  -target=google_cloud_run_v2_service.neuron_sandbox \
+  -target=google_secret_manager_secret_iam_member.sandbox_url_accessor \
+  -target=google_secret_manager_secret_iam_member.sandbox_anon_accessor \
+  -target=google_secret_manager_secret_iam_member.sandbox_service_accessor \
+  -target=google_secret_manager_secret_version.sandbox_supabase_url_placeholder \
+  -target=google_secret_manager_secret_version.sandbox_supabase_anon_key_placeholder \
+  -target=google_secret_manager_secret_version.sandbox_supabase_service_key_placeholder \
+  -target=google_secret_manager_secret.sandbox_supabase_url \
+  -target=google_secret_manager_secret.sandbox_supabase_anon_key \
+  -target=google_secret_manager_secret.sandbox_supabase_service_key \
+  -target=google_service_account.neuron_sandbox \
+  -target=google_artifact_registry_repository.sandbox
+
+# Then re-apply:
+terraform apply
+```
+
+If the Supabase project was provisioned, also delete it from the Supabase
+dashboard and re-create with a new name. The Secret Manager secrets carry
+forward as placeholders; rewrite them with the new project's values.
+
+## Files
+
+| File                                                  | What                                |
+|-------------------------------------------------------|-------------------------------------|
+| `servers/gcp/sandbox.tf`                              | All sandbox terraform               |
+| `servers/gcp/sandbox/README.md`                       | This document                       |
+| `~/Development/neuron-technologies/products/sandbox-stub/` | Stub source code (Go, 4 routes) |
diff --git a/servers/gcp/terraform.tfvars b/servers/gcp/terraform.tfvars
index f3475c2..08655d8 100644
--- a/servers/gcp/terraform.tfvars
+++ b/servers/gcp/terraform.tfvars
@@ -1,3 +1,4 @@
 cloudflare_zone_id_neurontechnologies = "e844374f203dca4944d77d40ca0710ae"
 cloudflare_api_key = "007bbefe03eac0e502c339423c50dd911776a"
 cloudflare_email   = "andersonwilliam85@gmail.com"
+cloudflare_account_id = "651161e0a3d321561b4c90b5bcd5f15b"
diff --git a/servers/gcp/variables.tf b/servers/gcp/variables.tf
index 3b42fba..0678419 100644
--- a/servers/gcp/variables.tf
+++ b/servers/gcp/variables.tf
@@ -41,6 +41,12 @@ variable "cloudflare_email" {
   type        = string
 }
 
+variable "cloudflare_account_id" {
+  description = "Cloudflare account ID (used for Zero Trust Access policies)"
+  type        = string
+  sensitive   = true
+}
+
 locals {
   project_id = var.project_id