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+# Sandboxed iframe blueprint apps
+
+How embedded first-party blueprint apps are rendered, isolated, and
+authorised inside Tangle Cloud.
+
+## Architecture summary
+
+```
+┌─ cloud.tangle.tools (parent) ────────────────────────────────────┐
+│                                                                  │
+│  ┌─ <iframe sandbox="allow-scripts allow-forms"> ─────────────┐  │
+│  │                                                            │  │
+│  │  trading-arena.blueprint.tangle.tools                      │  │
+│  │   • opaque origin (no allow-same-origin)                   │  │
+│  │   • cannot reach parent.localStorage / cookies / wallet    │  │
+│  │   • cannot navigate parent (no allow-top-navigation)       │  │
+│  │                                                            │  │
+│  └─ postMessage ▲ │ postMessage ▼ ─────────────────────────── ┘  │
+│                  │ │                                              │
+│   ┌──────────────┼─┼─────────────────────────────────────────┐   │
+│   │  useIframeBridge                                         │   │
+│   │   1. event.origin === manifest.origin (strict)           │   │
+│   │   2. event.source === iframe.contentWindow               │   │
+│   │   3. validateIframeRequest(payload)  (typed schema)      │   │
+│   │   4. checkRequestAllowed(req, manifest.iframe)           │   │
+│   │      ├─ contract+selector+chain allowlist                │   │
+│   │      └─ capability flags (read/switch/popups)            │   │
+│   │   5. surface IframeAppApprovalModal                      │   │
+│   │   6. on approve → useSendTransaction / useSignMessage    │   │
+│   │   7. postMessage result keyed on correlationId           │   │
+│   └──────────────────────────────────────────────────────────┘   │
+└──────────────────────────────────────────────────────────────────┘
+```
+
+The wallet flow stays in the parent. The iframe never touches
+`window.ethereum`. Signing requests bubble through `postMessage`
+with a correlationId; the parent renders its own approval UI and
+posts the result back.
+
+## Environment flags
+
+| Variable | Default | Purpose |
+|---|---|---|
+| `VITE_BLUEPRINT_IFRAME_ENABLED` | `false` | Same-day kill switch. When false, every iframe-mode manifest downgrades to link-out. |
+| `VITE_BLUEPRINT_IFRAME_PUBLISHERS` | `tangle,tangle-labs` (default) | Comma-separated publisher namespaces eligible for iframe rendering. Distinct from verified publishers. Adding entries is a governance call. |
+| `VITE_BLUEPRINT_IFRAME_HOST_SUFFIXES` | `.blueprint.tangle.tools,.blueprint.tangle.sh` | Wildcard host suffixes accepted as iframe sources. Each iframe app still needs a manifest entry; this just gates the URL shape. |
+
+## Onboarding a new iframe-eligible app
+
+1. **Deploy the bundle** to a subdomain matching one of the allowed
+   suffixes (e.g. `myapp.blueprint.tangle.tools`). Cloudflare Pages
+   recommended:
+
+   ```
+   wrangler pages project create myapp --production-branch=main
+   wrangler pages deploy build/client --project-name=myapp --branch=main
+   ```
+
+2. **Attach custom domain + DNS** (see ops runbook in tangle-network/dapp).
+
+3. **Drop a `_headers` file** in the build output:
+
+   ```
+   /*
+     Content-Security-Policy: frame-ancestors https://cloud.tangle.tools https://app.tangle.tools https://apps.tangle.tools
+     Permissions-Policy: camera=(), microphone=(), geolocation=(), payment=(), usb=(), bluetooth=()
+     Referrer-Policy: no-referrer
+     X-Content-Type-Options: nosniff
+     Strict-Transport-Security: max-age=63072000; includeSubDomains; preload
+   ```
+
+   Set cookies with `Domain=myapp.blueprint.tangle.tools` only —
+   never the parent registrable domain.
+
+4. **Publish the IPFS metadata** with the `blueprintUi.externalApp`
+   block:
+
+   ```json
+   {
+     "blueprintUi": {
+       "displayName": "My App",
+       "publisher": { "namespace": "tangle" },
+       "externalApp": {
+         "url": "https://myapp.blueprint.tangle.tools/",
+         "mode": "iframe",
+         "label": "Open My App",
+         "iframe": {
+           "appId": "myapp",
+           "allowedChainIds": [3799],
+           "contracts": [
+             {
+               "chainId": 3799,
+               "address": "0xabc...",
+               "selectors": ["0xa9059cbb"]
+             }
+           ],
+           "messages": [],
+           "allowReadAccount": true,
+           "allowChainSwitch": false,
+           "allowPopups": false
+         }
+       }
+     }
+   }
+   ```
+
+5. **(Non-Tangle namespaces only)** Add the namespace to
+   `VITE_BLUEPRINT_IFRAME_PUBLISHERS`. This is a governance call.
+
+6. **Flip `VITE_BLUEPRINT_IFRAME_ENABLED=true`** if it isn't already
+   on for this environment.
+
+## Manifest schema reference
+
+The `iframe` block is declarative — it defines what the iframe is
+*allowed* to ask the wallet to do. Anything outside is rejected
+before the approval modal surfaces.
+
+| Field | Type | Effect |
+|---|---|---|
+| `appId` | string | Stable identifier emitted in handshake. |
+| `allowedChainIds` | number[] | If non-empty, signing requests on other chains are rejected. |
+| `contracts` | `{chainId, address, selectors?}[]` | Per-contract allowlist. `selectors` is optional 4-byte selector list; omit for full-contract trust. |
+| `messages` | `{chainId, prefixes?}[]` | EIP-191 sign-message allowlist. |
+| `allowReadAccount` | bool | Iframe can ask for the connected account/chain without user prompt. |
+| `allowChainSwitch` | bool | Iframe can prompt the user to switch chains. |
+| `allowPopups` | bool | Sets `allow-popups[-to-escape-sandbox]`. Required for OAuth-style flows; widens attack surface, default off. |
+
+## Kill-switch flip (incident response)
+
+If something goes wrong with an iframe app:
+
+1. **Immediate**: `VITE_BLUEPRINT_IFRAME_ENABLED=false` + redeploy.
+   Every manifest downgrades to link-out automatically. ~5 min.
+
+2. **Per-publisher**: Remove the namespace from
+   `VITE_BLUEPRINT_IFRAME_PUBLISHERS`. Other iframe apps stay live.
+
+3. **Per-host**: Remove the host suffix from
+   `VITE_BLUEPRINT_IFRAME_HOST_SUFFIXES`. Useful when an entire
+   subdomain pattern is suspect.
+
+4. **Last resort**: Update the IPFS metadata to remove the
+   `externalApp.iframe` block. Slower (requires onchain manifest
+   refresh) but persists across env redeploys.
+
+## Threat model & invariants
+
+The full threat model lives in
+[issue #3171](https://github.com/tangle-network/dapp/issues/3171).
+Critical invariants this code enforces:
+
+- **Origin equality**: never `endsWith` / `startsWith` / regex on origin.
+  Reject anything that doesn't exactly match the manifest's parsed origin.
+- **Source equality**: `event.source === iframe.contentWindow`.
+  Defends against confused-deputy attacks where another whitelisted
+  origin posts at the parent.
+- **Bounded payloads**: 4KB messages, 128KB calldata, 128-char
+  ASCII-printable correlationIds. Defeats DoS via large
+  `structuredClone`.
+- **Wallet isolation**: iframe never gets `window.ethereum`. All
+  signing routes through the parent's wagmi flow with the user's
+  approval.
+- **No `*` `targetOrigin`**: parent always pins postMessage to the
+  manifest's exact origin.