fix(filesystem): ignore trailing newline in tail

[jstar0]

Description

Fix tailFile so a file's final newline is treated as a line terminator rather than an additional empty line. This makes tail=1 return the final content line for files that end with \n or \r\n.

Server Details

• Server: filesystem
• Changes to: file utility implementation and regression tests

Motivation and Context

When a file ends with a newline, the reverse chunk reader currently includes the synthetic empty segment after that terminator. Callers requesting the last line therefore receive an empty string instead of the final content line. The fix removes that synthetic segment only for the first chunk read from the end; line handling and chunk-boundary behavior remain unchanged.

How Has This Been Tested?

• npm exec --workspace @modelcontextprotocol/server-filesystem -- vitest run __tests__/lib.test.ts --reporter=dot — 47 passed
• npm run build --workspace @modelcontextprotocol/server-filesystem — passed

The regression covers a file containing line1\nline2\n and verifies that tailFile(path, 1) returns line2 and closes the file handle.

Breaking Changes

No. This corrects the returned value for files ending in a newline; files without a trailing newline retain their existing behavior.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Protocol Documentation
• My changes follows MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context

The change is limited to the filesystem server's existing tail operation and adds no protocol, configuration, or dependency changes.

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