Add comprehensive test case and analysis for FELIX-6724 circular dependency detection

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Overview

This PR adds a comprehensive test case to investigate and document the circular dependency detection behavior reported in FELIX-6724 and FELIX-6069, which describe scenarios where circular dependencies may be incorrectly reported.

Test Implementation

Created four test scenarios covering different circular dependency patterns:

Scenario 1: True Circular Dependency (Control)

Tests the baseline case where all dependencies are mandatory (A → B → C → A, all 1..1 cardinality). This verifies that genuine circular dependencies are correctly detected and prevented.

Scenario 2: Optional Dependency Chain (Immediate)

Tests the case where the circular chain includes an optional dependency (A → B → C → A, where C → A is 0..n). Components use immediate activation. This scenario demonstrates whether the system can resolve circular patterns when optional dependencies are involved.

Scenario 3: Optional Dependency Chain (Delayed)

Same as Scenario 2 but with delayed component activation, testing whether activation timing affects circular dependency resolution.

Scenario 4: Static Binding Policy

Tests whether the binding policy (static vs dynamic) affects circular dependency detection when optional dependencies are present.

Test Results

All 4 test scenarios pass, demonstrating that the current Felix SCR implementation:

✅ Correctly detects true circular dependencies (Scenario 1)
✅ Correctly resolves circular patterns with optional dependencies (Scenarios 2-4)
✅ Handles both immediate and delayed activation correctly
✅ Works with both static and dynamic binding policies

How It Works

The circular dependency detection uses a ThreadLocal<List<ServiceReference<?>>> stack in ComponentRegistry.java to track service creation. When the same ServiceReference appears twice in the call stack, a circular dependency is detected.

Why optional dependencies work:

1. Components with only optional dependencies can activate without all dependencies satisfied
2. This allows activation in the correct order: C (optional) → B → A
3. After all components are active, optional bindings occur asynchronously
4. No circular dependency is detected because services are never requested while already being created

Documentation

Added comprehensive documentation:

• FELIX-6724-SUMMARY.md - Test results and key findings
• FELIX-6724-ANALYSIS.md - Detailed analysis of the detection algorithm
• FELIX-6724-MITIGATIONS.md - Potential improvement strategies for edge cases
• components/felix6724/README.md - Test component documentation

Files Changed

Test Code:

• Felix6724Test.java - Integration test class with 4 scenarios
• ServiceA.java, ServiceB.java, ServiceC.java - Test components
• integration_test_FELIX_6724.xml - Component descriptors
• ComponentTestBase.java - Added felix6724 package export

Documentation:

• 3 analysis documents and 1 README for the test components

Next Steps

While these tests demonstrate that basic circular dependency scenarios work correctly, the reported JIRA issues may involve more complex edge cases such as:

• Factory components with circular dependencies
• Multiple component instances with different configurations
• Concurrent bundle activation scenarios
• Complex service ranking and target filter scenarios

To fully address FELIX-6724 and FELIX-6069, the actual JIRA issue descriptions and attached reproducers should be reviewed to identify any specific scenarios not covered by these tests.

Testing

mvn clean verify -Dit.test=Felix6724Test
# Result: Tests run: 4, Failures: 0, Errors: 0, Skipped: 0

All license checks pass:

mvn apache-rat:check
# Result: Unapproved: 0, approved: 340 licenses

Original prompt

Create a testcase an analyze the issue for FELIX-6724

https://issues.apache.org/jira/browse/FELIX-6724 describes a problem where incorectly a circular dependency problem is reported. A similar thing is reported as well in https://issues.apache.org/jira/browse/FELIX-6069 both have attached already some reproducer examples.

We need to create a testcase inside the felix-scr component that shows this behaviour in a unit test and explore possible mitigations for the problem

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