chore: raise test coverage to 80 percent

[jlouvel]

Related Issue

Closes #188

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What does this PR do?

Increases JaCoCo test coverage from 67.47% to 80.01% (instruction-level) by adding targeted branch and edge-case tests across high-miss classes.

Approach: iteratively identified the classes with the most uncovered instructions via jacoco.csv, wrote focused tests for guard clauses, error paths, and fallback branches, verified each batch with the full suite, and repeated until the 80% threshold was crossed.

Coverage results

Metric	Before	After
Instruction	67.47%	80.01%
Line	68.87%	80.34%
Branch	54.31%	69.34%

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Tests

New test classes (6):

• OperationStepExecutorBranchTest — orchestration private/branch coverage
• JettyStreamableHandlerTest — MCP HTTP transport POST/GET/DELETE behavior
• ProtocolDispatcherCoverageTest — protocol error envelopes and edge cases
• ResourceHandlerDynamicTest — dynamic resource execution and fallback mapping
• InputParameterSerializerTest — input serializer nested/property branches
• OutputParameterSerializerTest — output serializer mapping/value semantics

Expanded test classes (5):

• ConverterTest — format guard clauses, JSONPath root selectors, maxLength edge cases
• ResolverTest — resolver and mapping branch paths
• OperationStepExecutorIntegrationTest — invalid call/mode paths
• ResourceHandlerSafetyTest — static-resource safety and template edge cases
• ResourceRestletTest — REST response/fallback behavior, forward-mode header propagation

Validation: mvn test --no-transfer-progress → 328 tests, 0 failures, 0 errors, 2 skipped, BUILD SUCCESS

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Checklist

• CI is green (build, tests, schema validation, security scans)
• Rebased on latest main
• Small and focused — one concern per PR
• Commit messages follow Conventional Commits

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Agent Context (optional)

agent_name: GitHub Copilot
llm: Claude Opus 4.6
tool: VS Code Copilot Chat
confidence: high
source_event: "Issue #188 — increase test coverage to 80%"
discovery_method: code_review
review_focus: src/test/java/io/naftiko/**