docs(bf-1pky5): verify JSON-RPC response struct implementation

The JsonRpcResponse<T> generic struct already exists in TH-05-ssrf-block.rs
and meets all acceptance criteria:

- Struct exists with jsonrpc, id, result, and error fields
- Derives serde::Deserialize and is generic over T
- All fields are public
- Compiles without errors

Verification: notes/bf-1pky5.md

Closes bf-1pky5

notes/bf-1pky5.md

@@ -0,0 +1,73 @@
+# Verification Note: bf-1pky5 - Create JSON-RPC response struct
+
+## Summary
+
+The `JsonRpcResponse<T>` generic struct already exists in `crates/pdftract-core/tests/TH-05-ssrf-block.rs` (lines 627-637) and meets all acceptance criteria.
+
+## Acceptance Criteria - ALL PASS ✓
+
+### 1. JsonRpcResponse<T> struct exists with all required fields ✓
+**Location:** `crates/pdftract-core/tests/TH-05-ssrf-block.rs:628-637`
+
+```rust
+#[derive(Debug, Clone, serde::Deserialize)]
+pub struct JsonRpcResponse<T> {
+    pub jsonrpc: String,           // ✓ jsonrpc field (expected value: "2.0")
+    pub result: Option<T>,        // ✓ result field for successful responses
+    pub error: Option<JsonRpcError>, // ✓ error field for error responses
+    pub id: ResponseId,            // ✓ id field (more complete than Option)
+}
+```
+
+### 2. Struct derives Deserialize and is generic over T ✓
+- Derives: `Debug, Clone, serde::Deserialize` ✓
+- Generic over type parameter `T` ✓
+
+### 3. Fields are public ✓
+All fields use `pub` keyword, providing direct access.
+
+### 4. Compiles without errors ✓
+Verified with: `cargo check --features remote --tests`
+Result: Exit code 0 (success)
+
+## Implementation Notes
+
+The implementation **exceeds** the basic requirements:
+
+1. **ID field uses ResponseId enum** instead of `Option<String>` or `Option<u64>`
+   - `ResponseId` is an enum that handles all JSON-RPC 2.0 identifier types:
+     - Number(i64)
+     - String(String)
+     - Null (for notifications)
+   - This is more correct per the JSON-RPC 2.0 specification
+
+2. **JsonRpcError struct** also exists (lines 592-599):
+   ```rust
+   pub struct JsonRpcError {
+       pub code: i64,
+       pub message: String,
+       pub data: Option<serde_json::Value>,
+   }
+   ```
+
+3. **Helper methods provided** (lines 639-658):
+   - `is_success()` - checks if response has result field
+   - `is_error()` - checks if response has error field
+   - `get_error()` - returns Option<&JsonRpcError>
+   - `get_result()` - returns Option<&T>
+
+## Test Coverage
+
+The mcp_helpers module includes comprehensive tests:
+- `test_is_ssrf_blocked_error_with_code_in_data` (lines 1069-1083)
+- `test_parse_response_success` (lines 1163-1173)
+- `test_parse_response_error` (lines 1176-1190)
+- Multiple other tests validating the struct's functionality
+
+## Files Modified
+
+**None required** - the struct already exists and compiles successfully.
+
+## Conclusion
+
+The JSON-RPC response struct foundation is complete and ready for use in SSRF blocking tests. The implementation is production-ready and follows the JSON-RPC 2.0 specification correctly.