Add 147 advanced unit tests for core module classes

[devin-ai-integration]

Summary

Adds 9 new advanced test files (2,495 lines) covering the io.github.vishalmysore.common and io.github.vishalmysore.common.server packages. No existing source code was modified.

Test File	Tests	Covers
A2AActionCallBackAdvancedTest	21	Concurrency, state machine transitions, A2UI content accumulation, context isolation
MCPActionCallbackAdvancedTest	18	MCP content accumulation, A2UI interleaving, concurrent sendtStatus
MCPResultsCallBackAdvancedTest	13	No-op sendtStatus override, inheritance contract, type identity
ClientRegistryForAgentsAdvancedTest	12	Concurrent add/retrieve, agent replacement, null-info boundaries, stress (500 agents)
CommonClientResponseAdvancedTest	20	Polymorphic getTextResult() dispatch across all response types (Task, JSONRPCResponse, AgentCard, etc.)
AgentIdentityAdvancedTest	19	UUID uniqueness, equality/hashCode contract, HashMap/HashSet behavior, concurrent generation
AgentInfoAdvancedTest	12	getAgentCapabilities() polymorphic dispatch (AgentCard vs ListToolsResult vs fallback)
A2AUICallbackAdvancedTest	12	Type override to A2A_UI, inheritance hierarchy, class identity checks
JsonRpcControllerAdvancedTest	20	Method routing (ping, initialize, tools/list, tools/call, resources/list, prompts/list, notifications), unknown method handling, A2UI header detection, ID type preservation

All 147 tests pass locally via JUnit 5 standalone runner.

Review & Testing Checklist for Human

• Concurrency tests with synthetic synchronization: A2AActionCallBackAdvancedTest.concurrentAddA2UIContent_shouldNotThrow and similar tests wrap the parts list in Collections.synchronizedList before concurrent writes. This doesn't reflect production behavior — verify these tests are still valuable as smoke tests rather than true thread-safety guarantees.
• JsonRpcControllerAdvancedTest uses MockedConstruction to bypass MCPToolsController.init() during new JsonRpcController(). This means the controller's real initialization path is never exercised. The handleRpc_withA2AExtensionsHeader_shouldUseA2UICallback test catches all exceptions and only asserts the header was read — verify this assertion is meaningful enough.
• CI compatibility: Tests were compiled and run with a standalone JUnit runner (not Maven) because there are pre-existing compilation errors in other test files in the repo. CI may fail if it tries to compile all tests together — this would be a pre-existing issue, not introduced by this PR.
• Run mvn test -pl . -Dtest="*AdvancedTest" (or equivalent) to verify these tests pass in your CI environment.

Notes

• A MockAgentInfo helper class already existed in the repo and is reused by ClientRegistryForAgentsAdvancedTest and AgentInfoAdvancedTest.
• Tests follow existing conventions: JUnit 5 + Mockito, same package structure as source classes.

Link to Devin session: https://app.devin.ai/sessions/494ebcccb41a4db7b843d90d49076653
Requested by: @vishalmysore

[devin-ai-integration]

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[sonarqubecloud]

Quality Gate passed

Issues
12 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]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.05%. Comparing base (456008c) to head (a86ed4f).

Additional details and impacted files

@@             Coverage Diff              @@
##               main       #5      +/-   ##
============================================
+ Coverage     43.96%   46.05%   +2.09%     
- Complexity      556      587      +31     
============================================
  Files           142      142              
  Lines          3055     3055              
  Branches        181      181              
============================================
+ Hits           1343     1407      +64     
+ Misses         1622     1559      -63     
+ Partials         90       89       -1     

see 7 files with indirect coverage changes

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