[BUG] Claude.ai ignores frameDomains (and other CSP fields) declared in MCP Apps _meta.ui.csp — iframe blocked by hardcoded frame-src

### What happened?

## Summary

Claude.ai's MCP Apps sandbox does not respect the `frameDomains`, `connectDomains`, or `resourceDomains` fields declared in a UI resource's `_meta.ui.csp` object. Instead, a hardcoded CSP of `frame-src 'self' blob: data:` is enforced, blocking any nested iframes from declared origins. This violates the MCP Apps specification (SEP-1865, section 5), which states:

> "The Sandbox MUST… If `frameDomains` is provided, allow nested iframes from declared origins."

The same MCP server works correctly on other hosts (ChatGPT, MCP-Jam) that properly respect the declared CSP fields.

## Environment

- **Host:** Claude.ai (web interface, claude.ai)
- **Browser:** Brave 144 / Chromium-based (macOS 26.2.0, ARM64)
- **MCP Server:** Revieve Skincare Advisor (`https://add-mcp-server--revieve-platform-mcp-server.netlify.app`)

## Resource `_meta.ui.csp` Declaration

The MCP server correctly declares CSP requirements in the UI resource metadata:

```typescript
{
uri: resourceUri,
mimeType: RESOURCE_MIME_TYPE,
text: pageHTML,
_meta: {
ui: {
csp: {
resourceDomains: [
"https://cdn.revieve.com/",
"https://www.googletagmanager.com/",
"https://d38knilzwtuys1.cloudfront.net",
"http://localhost:3000/",
"https://add-mcp-server--revieve-platform-plugin.netlify.app/",
ASTRO_DEV_URL,
],
connectDomains: [
"https://cdn.revieve.com/",
"https://partner-test.revieve.com",
"https://d38knilzwtuys1.cloudfront.net",
"https://sst.revieve.com",
],
frameDomains: [
"https://cdn.revieve.com",
"https://d38knilzwtuys1.cloudfront.net",
],
baseUriDomains: ["https://cdn.revieve.com/"],
},
},
},
}
```

## Observed Behavior

Claude.ai enforces the following CSP on the sandbox iframe, **completely ignoring** all declared domains:

```
frame-src 'self' blob: data:
connect-src 'self' https://cdn.revieve.com https://partner-test.revieve.com https://d38knilzwtuys1.cloudfront.net
```

### Console Errors

**1. `frame-src` violation — nested iframe blocked:**

```
Framing 'https://d38knilzwtuys1.cloudfront.net/' violates the following Content Security Policy
directive: "frame-src 'self' blob: data:". The request has been blocked.
```

**2. `connect-src` violation — analytics/telemetry blocked:**

```
Connecting to 'https://sst.revieve.com/g/collect?...' violates the following Content Security Policy
directive: "connect-src 'self' https://cdn.revieve.com https://partner-test.revieve.com
https://d38knilzwtuys1.cloudfront.net". The action has been blocked.
```

```
Fetch API cannot load https://sst.revieve.com/g/collect?...
Refused to connect because it violates the document's Content Security Policy.
```

### What did you expect to happen?

## Expected Behavior

Per the MCP Apps specification (SEP-1865), the host sandbox **must** read `_meta.ui.csp` and dynamically apply the declared domains to the corresponding CSP directives:

- `frameDomains` → should be added to `frame-src`
- `connectDomains` → should be added to `connect-src`
- `resourceDomains` → should be added to relevant resource directives (`script-src`, `img-src`, etc.)

The expected enforced CSP should include at minimum:

```
frame-src 'self' blob: data: https://cdn.revieve.com https://d38knilzwtuys1.cloudfront.net
connect-src 'self' https://cdn.revieve.com https://partner-test.revieve.com https://d38knilzwtuys1.cloudfront.net https://sst.revieve.com
```

### Steps to reproduce

## Steps to Reproduce

1. Go to Claude.ai
2. Connect the Revieve Skincare Advisor MCP server
3. Trigger any tool that returns a UI resource (e.g., `Show me the skincare advisor widget`)
4. Open browser DevTools → Console
5. Observe `frame-src` and `connect-src` CSP violation errors
6. The widget fails to render its iframe content

### Area

Resource Handling

### MCP Server (if applicable)

Revieve Skincare Advisor (`https://add-mcp-server--revieve-platform-mcp-server.netlify.app/api/mcp`)

### Error messages or logs

```shell
Framing 'https://d38knilzwtuys1.cloudfront.net/' violates the following Content Security Policy directive: "frame-src 'self' blob: data:". The request has been blocked.

js?id=G-VBZ5XNENGP:213 Connecting to 'https://sst.revieve.com/g/collect?v=2&tid=G-VBZ5XNENGP>m=45je6221v892154687za200zd892154687&_p=1770218131389&gcs=G111&gcd=13t3tPt2t5l1&npa=0&dma_cps=syphamo&dma=1&cid=715284458.1770131200&ul=en-us&sr=1512x982&_fplc=0&uaa=arm&uab=64&uafvl=Not(A%253ABrand%3B8.0.0.0%7CChromium%3B144.0.0.0%7CBrave%3B144.0.0.0&uamb=0&uam=&uap=macOS&uapv=26.2.0&uaw=0&frm=2&pscdl=noapi&_eu=AAAAAAQ&_s=1&tag_exp=103116026~103200004~104527907~104528501~104684208~104684211~115616985~115938466~115938469~116185181~116185182~116988315...ilzwtuys1.cloudfront.net%26resource-src%3Dhttps%253A%252F%252Fcdn.revieve.com%252F%2Bhttps%253A%252F%252Fwww.googletagmanager.com%252F%2Bhttps%253A%252F%252Fd38knilzwtuys1.cloudfront.net%2Bhttp%253A%252F%252Flocalhost%253A3000%252F%2Bhttps%253A%252F%252Fadd-mcp-server--revieve-platform-plugin.netlify.app%252F%2Bhttps%253A%252F%252Fadd-mcp-server--revieve-platform-mcp-server.netlify.app%2Bhttps%253A%252F%252Fassets.claude.ai&dt=-&_tu=RA&en=page_view&_ss=1&_ee=1&ep.identifier=Revieve%20skincaredemo&tfd=1380' violates the following Content Security Policy directive: "connect-src 'self' https://cdn.revieve.com https://partner-test.revieve.com https://d38knilzwtuys1.cloudfront.net". The action has been blocked.
fd @ js?id=G-VBZ5XNENGP:213
js?id=G-VBZ5XNENGP:213 Fetch API cannot load https://sst.revieve.com/g/collect?v=2&tid=G-VBZ5XNENGP>m=45je6221v892154687za200zd892154687&_p=1770218131389&gcs=G111&gcd=13t3tPt2t5l1&npa=0&dma_cps=syphamo&dma=1&cid=715284458.1770131200&ul=en-us&sr=1512x982&_fplc=0&uaa=arm&uab=64&uafvl=Not(A%253ABrand%3B8.0.0.0%7CChromium%3B144.0.0.0%7CBrave%3B144.0.0.0&uamb=0&uam=&uap=macOS&uapv=26.2.0&uaw=0&frm=2&pscdl=noapi&_eu=AAAAAAQ&_s=1&tag_exp=103116026~103200004~104527907~104528501~104684208~104684211~115616985~115938466~115938469~116185181~116185182~116988315...ilzwtuys1.cloudfront.net%26resource-src%3Dhttps%253A%252F%252Fcdn.revieve.com%252F%2Bhttps%253A%252F%252Fwww.googletagmanager.com%252F%2Bhttps%253A%252F%252Fd38knilzwtuys1.cloudfront.net%2Bhttp%253A%252F%252Flocalhost%253A3000%252F%2Bhttps%253A%252F%252Fadd-mcp-server--revieve-platform-plugin.netlify.app%252F%2Bhttps%253A%252F%252Fadd-mcp-server--revieve-platform-mcp-server.netlify.app%2Bhttps%253A%252F%252Fassets.claude.ai&dt=-&_tu=RA&en=page_view&_ss=1&_ee=1&ep.identifier=Revieve%20skincaredemo&tfd=1380. Refused to connect because it violates the document's Content Security Policy.
fd @ js?id=G-VBZ5XNENGP:213
js?id=G-VBZ5XNENGP:213 Connecting to 'https://sst.revieve.com/g/collect?v=2&tid=G-VBZ5XNENGP>m=45je6221v892154687za200zd892154687&_p=1770218131389&gcs=G111&gcd=13t3tPt2t5l1&npa=0&dma_cps=syphamo&dma=1&cid=715284458.1770131200&ul=en-us&sr=1512x982&_fplc=0&uaa=arm&uab=64&uafvl=Not(A%253ABrand%3B8.0.0.0%7CChromium%3B144.0.0.0%7CBrave%3B144.0.0.0&uamb=0&uam=&uap=macOS&uapv=26.2.0&uaw=0&frm=2&pscdl=noapi&_eu=AEAAAAQ&_s=2&tag_exp=103116026~103200004~104527907~104528501~104684208~104684211~115616985~115938466~115938469~116185181~116185182~116988315....cloudfront.net%26resource-src%3Dhttps%253A%252F%252Fcdn.revieve.com%252F%2Bhttps%253A%252F%252Fwww.googletagmanager.com%252F%2Bhttps%253A%252F%252Fd38knilzwtuys1.cloudfront.net%2Bhttp%253A%252F%252Flocalhost%253A3000%252F%2Bhttps%253A%252F%252Fadd-mcp-server--revieve-platform-plugin.netlify.app%252F%2Bhttps%253A%252F%252Fadd-mcp-server--revieve-platform-mcp-server.netlify.app%2Bhttps%253A%252F%252Fassets.claude.ai&dt=-&_tu=RA&en=scroll&ep.identifier=Revieve%20skincaredemo&epn.percent_scrolled=90&tfd=6831' violates the following Content Security Policy directive: "connect-src 'self' https://cdn.revieve.com https://partner-test.revieve.com https://d38knilzwtuys1.cloudfront.net". The action has been blocked.
fd @ js?id=G-VBZ5XNENGP:213
js?id=G-VBZ5XNENGP:213 Fetch API cannot load https://sst.revieve.com/g/collect?v=2&tid=G-VBZ5XNENGP>m=45je6221v892154687za200zd892154687&_p=1770218131389&gcs=G111&gcd=13t3tPt2t5l1&npa=0&dma_cps=syphamo&dma=1&cid=715284458.1770131200&ul=en-us&sr=1512x982&_fplc=0&uaa=arm&uab=64&uafvl=Not(A%253ABrand%3B8.0.0.0%7CChromium%3B144.0.0.0%7CBrave%3B144.0.0.0&uamb=0&uam=&uap=macOS&uapv=26.2.0&uaw=0&frm=2&pscdl=noapi&_eu=AEAAAAQ&_s=2&tag_exp=103116026~103200004~104527907~104528501~104684208~104684211~115616985~115938466~115938469~116185181~116185182~116988315....cloudfront.net%26resource-src%3Dhttps%253A%252F%252Fcdn.revieve.com%252F%2Bhttps%253A%252F%252Fwww.googletagmanager.com%252F%2Bhttps%253A%252F%252Fd38knilzwtuys1.cloudfront.net%2Bhttp%253A%252F%252Flocalhost%253A3000%252F%2Bhttps%253A%252F%252Fadd-mcp-server--revieve-platform-plugin.netlify.app%252F%2Bhttps%253A%252F%252Fadd-mcp-server--revieve-platform-mcp-server.netlify.app%2Bhttps%253A%252F%252Fassets.claude.ai&dt=-&_tu=RA&en=scroll&ep.identifier=Revieve%20skincaredemo&epn.percent_scrolled=90&tfd=6831. Refused to connect because it violates the document's Content Security Policy.
```

### Additional context

## Cross-Host Comparison

| Host | `frameDomains` Respected? | Widget Renders? |
|------|--------------------------|-----------------|
| Claude.ai | ❌ No — hardcoded `frame-src 'self' blob: data:` | ❌ Blocked |
| ChatGPT | ✅ Yes | ✅ Works |
| MCP-Jam | ✅ Yes | ✅ Works |

## Impact

This is a **spec compliance issue** that breaks any MCP App relying on nested iframes from external origins — a common pattern for widget-based integrations (embedded dashboards, third-party UI components, etc.). It effectively makes `frameDomains` non-functional on Claude.ai.

## Suggested Fix

Claude.ai's MCP Apps sandbox renderer should:

1. Read the `_meta.ui.csp` object from the UI resource
2. Dynamically merge `frameDomains` into the sandbox's `frame-src` directive
3. Dynamically merge `connectDomains` into `connect-src`
4. Dynamically merge `resourceDomains` into the appropriate resource directives

This is likely a small change in how the sandbox iframe's CSP header/meta tag is constructed before rendering.