[test-improver] Improve tests for mcp package connection utilities

[github-actions]

File Analyzed

• Test File: internal/mcp/connection_stderr_test.go
• Package: internal/mcp
• Lines of Code: 38 → 261 (substantial improvement)

Improvements Made

1. Replaced Documentation-Only Test With Real Assertions

The original file contained a single TestConnection_MultipleServersStderrLogging test that consisted entirely of comment-style documentation and three t.Log() calls — no assertions whatsoever. It was essentially a code comment dressed as a test. This PR replaces it with meaningful unit tests that actually verify behavior.

2. New Coverage: NormalizeInputSchema (Previously Untested)

internal/mcp/schema.go exports NormalizeInputSchema but had zero test coverage. Added comprehensive table-driven tests:

• ✅ TestNormalizeInputSchema — 5 cases covering nil schema, object schema with/without properties, schema with properties but no type, empty schema
• ✅ TestNormalizeInputSchema_NonObjectTypes — string, array, and integer schemas are returned as-is (no properties added)
• ✅ TestNormalizeInputSchema_AdditionalProperties — schemas with additionalProperties skip empty-properties injection
• ✅ TestNormalizeInputSchema_DoesNotMutateOriginal — verifies the function never mutates the caller's schema map
• ✅ TestNormalizeInputSchema_NilSchemaReturnsIndependentMaps — each nil call returns an independent map (mutation isolation)

3. New Coverage: connection.go Helper Functions

Three unexported helpers in connection.go were also untested:

• ✅ TestMarshalToResponse — 3 sub-tests: map input, nil input, struct input; verifies JSONRPC=2.0 and correct JSON round-trip
• ✅ TestRequireSession — verifies that a nil session returns a clear "SDK session not available" error
• ✅ TestCallSDKMethod_UnsupportedMethod — verifies the default switch case returns an "unsupported method: ..." error
• ✅ TestCallSDKMethod_SessionRequiredMethods — all 6 MCP methods (tools/list, tools/call, resources/list, resources/read, prompts/list, prompts/get) return a session error when session is nil

4. Preserved Documentation Value

The serverID attribution behavior (the original reason for the file) is now documented via TestConnection_ServerIDField, which actually asserts that the serverID field is stored correctly on the Connection struct, while the doc comment preserves the historical context about before/after log line attribution.

Why These Changes?

connection_stderr_test.go was the weakest test file in the repository — it had no assertions and provided zero coverage. Meanwhile, schema.go's NormalizeInputSchema function (which has 5 distinct code paths) was completely untested despite being called on every tool registration. This PR addresses both gaps in a single file by adding real tests for the mcp package's utility functions.

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