[mcp] Implement get_critical_path tool (Phase 3 Step 4)

[Copilot]

Phase 3: Implement get_critical_path Tool (Tool #4)

Part of #7827

Summary

This PR implements the get_critical_path MCP tool as part of Phase 3 of the Jaeger MCP server implementation. The tool identifies the sequence of spans forming the critical latency path (the blocking execution path) in a distributed trace.

Implementation Details

1. Critical Path Algorithm (Port from UI)

   • Ported the critical path computation algorithm from TypeScript (jaeger-ui) to Go
   • Implements recursive algorithm to find Last Finishing Child (LFC) spans
   • Handles edge cases like overflowing child spans and FOLLOWS_FROM relationships
   • Includes comprehensive unit tests matching UI test cases

2. MCP Tool Handler

   • Created get_critical_path tool handler that:
     • Accepts trace ID as input
     • Fetches trace data via QueryService
     • Computes critical path using the ported algorithm
     • Returns formatted output with span details, service names, and timing information
   • Includes proper error handling and input validation

3. Integration

   • Registered tool in MCP server
   • Defined JSON schemas for input/output types
   • Connected handler to QueryService from jaegerquery extension

Testing & Coverage

• ✅ All unit tests passing
• ✅ criticalpath package: 95.9% coverage
• ✅ handlers package: 96.4% coverage
• ✅ Comprehensive test cases including edge cases
• ✅ make fmt passes
• ✅ make lint passes with 0 issues
• ✅ make test passes (for jaegermcp package)

Changes

• Created internal/criticalpath/ package with algorithm implementation
• Created internal/handlers/ package with tool handlers
• Created internal/types/ package with MCP tool types
• Updated MCP server to register the new tool
• Updated README with current implementation status
• Added comprehensive tests achieving >95% code coverage

Original prompt

implement phase 3 step 4 from ADR 002 as part of issue #7827. State Part of #7827 in PR description. Run make fmt make lint and make test to success everytime before pushing to remove branch.

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[codecov]

Codecov Report

❌ Patch coverage is 50.90253% with 136 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.67%. Comparing base (55fbe8c) to head (649de18).

Files with missing lines	Patch %	Lines
...n/jaegermcp/internal/handlers/get_critical_path.go	0.00%	74 Missing ⚠️
...ension/jaegermcp/internal/criticalpath/sanitize.go	41.07%	30 Missing and 3 partials ⚠️
...germcp/internal/criticalpath/get_child_of_spans.go	36.00%	13 Missing and 3 partials ⚠️
...on/jaegermcp/internal/criticalpath/criticalpath.go	86.44%	4 Missing and 4 partials ⚠️
cmd/jaeger/internal/extension/jaegermcp/server.go	57.14%	3 Missing ⚠️
...ension/jaegermcp/internal/criticalpath/find_lfc.go	90.00%	1 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (50.90%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project check has failed because the head coverage (94.67%) is below the target coverage (95.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7857      +/-   ##
==========================================
- Coverage   95.46%   94.67%   -0.79%     
==========================================
  Files         300      306       +6     
  Lines       15731    16008     +277     
==========================================
+ Hits        15017    15156     +139     
- Misses        560      686     +126     
- Partials      154      166      +12     

Flag	Coverage Δ
badger_v1	9.18% <ø> (ø)
badger_v2	1.93% <ø> (ø)
cassandra-4.x-v1-manual	13.58% <ø> (ø)
cassandra-4.x-v2-auto	1.92% <ø> (ø)
cassandra-4.x-v2-manual	1.92% <ø> (ø)
cassandra-5.x-v1-manual	13.58% <ø> (ø)
cassandra-5.x-v2-auto	1.92% <ø> (ø)
cassandra-5.x-v2-manual	1.92% <ø> (ø)
clickhouse	1.97% <ø> (ø)
elasticsearch-6.x-v1	17.54% <ø> (ø)
elasticsearch-7.x-v1	17.57% <ø> (ø)
elasticsearch-8.x-v1	17.72% <ø> (ø)
elasticsearch-8.x-v2	1.93% <ø> (ø)
elasticsearch-9.x-v2	1.93% <ø> (ø)
grpc_v1	8.84% <ø> (ø)
grpc_v2	1.93% <ø> (ø)
kafka-3.x-v2	1.93% <ø> (ø)
memory_v2	1.93% <ø> (ø)
opensearch-1.x-v1	17.61% <ø> (ø)
opensearch-2.x-v1	17.61% <ø> (ø)
opensearch-2.x-v2	1.93% <ø> (ø)
opensearch-3.x-v2	1.93% <ø> (ø)
query	1.93% <ø> (ø)
tailsampling-processor	0.55% <ø> (ø)
unittests	93.31% <50.90%> (-0.76%)	⬇️

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[yurishkuro]

@copilot Make sure all new code has good test coverage, no less than 95%.

[Copilot]

@copilot Make sure all new code has good test coverage, no less than 95%.

Done. Added comprehensive tests achieving >95% coverage for all new code:

• criticalpath package: 95.9% coverage
• handlers package: 96.4% coverage

Commit: eb49c13