fix(jsonrpc): prevent nil pointer panic on unregistered service path

[cvictory]

Bug

• Symptom: JSON-RPC server panics with nil pointer dereference when a request targets an unregistered service path
• Root cause: ExporterMap().Load(path) in serveRequest() discards the ok return value. When path is not registered, exporter is nil, and the type assertion exporter.(*JsonrpcExporter) panics.
• Issue: [BUG] Nil pointer dereference panic when JSON-RPC request targets unregistered service path #3310

Fix

• Check the ok return value from ExporterMap().Load(path)
• When !ok, return perrors.Errorf("service not found: %s", path) instead of proceeding to type-assert a nil value

Verification

• New test: TestHandlePkg_UnregisteredPath — sends valid JSON-RPC request to unregistered path, asserts HTTP 500 with "service not found" (no panic)
• Existing tests: All 6 TestHandlePkg_ContentType sub-tests pass
• Full package: All 9 tests in protocol/jsonrpc pass
• Static analysis: go vet ./protocol/jsonrpc/ passes

Closes #3310

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.22%. Comparing base (ea93b8a) to head (6499e1b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3314      +/-   ##
==========================================
+ Coverage   50.79%   51.22%   +0.43%     
==========================================
  Files         488      488              
  Lines       44203    36566    -7637     
==========================================
- Hits        22451    18730    -3721     
+ Misses      20242    16322    -3920     
- Partials     1510     1514       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

Fixes a JSON-RPC server panic when requests target an unregistered service path by validating exporter lookup results and returning a clear error instead of type-asserting a nil value.

Changes:

• Add ok check around ExporterMap().Load(path) in serveRequest() and return service not found when missing.
• Add a regression test to ensure unregistered paths return HTTP 500 with an explanatory error (and do not panic).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
protocol/jsonrpc/server.go	Prevents nil pointer panic by handling missing exporter lookups with a returned error.
protocol/jsonrpc/server_test.go	Adds coverage for unregistered-path requests to verify error response and no panic.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[AlexStocks]

@cvictory 展图，todo：
1 把文件冲突解决下。
2 后面提pr，先提到 develop 分支。
thx again。

[Alanxtl]

this issue have been solved in #3312 is this pr still needed?