fix(mcp_server): coerce integer progressToken before slicing in debug log

[juancarlosm]

Summary

MCP tools/call through the proxy crashes with TypeError: 'int' object is not subscriptable when the client sends an integer progressToken. The MCP spec allows progressToken to be string | integer, but _capture_host_progress_callback logged host_token[:8], which only works for strings. Because the f-string is built before verbose_logger.debug(...) runs, it raises even with debug logging disabled, and the exception aborts the whole tool call before the backend server is dispatched (backend logs stay clean, so it looks like a gateway/auth fault).

Fixes #32181.

Changes

• Extract the token formatting into _format_progress_token_for_log(), coercing the token to str before slicing.
• Add a parametrized regression test covering integer and string tokens.

Reproduce

Call any tool with an integer _meta.progressToken (e.g. {"progressToken": 1}). Clients such as Claude Code send monotonically increasing integer tokens by default. A string or absent token does not trigger it.

Testing

_format_progress_token_for_log(123456789) → "12345678..." (previously raised); "abcdefghij" → "abcdefgh..." unchanged.

[greptile-apps]

Greptile Summary

This PR fixes a crash in _capture_host_progress_callback where logging host_token[:8] raised TypeError: 'int' object is not subscriptable when the MCP client sends an integer progressToken (e.g. Claude Code's monotonically-increasing tokens). The fix extracts a tiny helper that coerces the token to str before slicing.

• server.py: New _format_progress_token_for_log() function converts the token via str() before slicing to 8 characters; the debug log call is updated to use it.
• test_mcp_server.py: Parametrized regression test verifies both integer (123456789 → "12345678...") and string ("abcdefghij" → "abcdefgh...") tokens are handled correctly.

Confidence Score: 5/5

Safe to merge — the change is a minimal, targeted fix to a debug log line with no impact on request routing or auth logic.

The only changed production code is a single helper function and one updated call site in a debug log path. The fix is correct: str() before slicing handles both str and int tokens as the MCP spec requires. A parametrized regression test is included and covers both cases. No behaviour beyond the log formatting is altered.

No files require special attention.

Important Files Changed

Filename	Overview
litellm/proxy/_experimental/mcp_server/server.py	Extracts _format_progress_token_for_log() to coerce progressToken to str before slicing, fixing the TypeError when an integer token is received. The surrounding call site is updated accordingly.
tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server.py	Adds a parametrized regression test covering both integer and string progressToken values — pure unit test, no network calls.

_{Reviews (1): Last reviewed commit: "fix(mcp_server): coerce integer progress..." | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[Geod24]

The related issue has been closed by another PR (#32402), I assume this can be safely closed ?