Part of #1195 — Phase 2
Blocked by: #1175 (MCP DALIA policy layer — sanitization hooks into PolicyEnforcer middleware)

Apply sanitization to all MCP server responses before they enter agent context.

Crates: zeph-mcp
Depends on: SEC-1.4, #1175

Tasks:

• MCP tool call results tagged ExternalUntrusted with server name as source
• Apply ContentSanitizer in PolicyEnforcer response path (post-DALIA middleware)
• Per-server trust override in config (future: trusted servers skip quarantine)
• Unit tests with mock MCP response containing injection payload

Files: crates/zeph-mcp/src/client.rs, crates/zeph-mcp/src/policy.rs