git: an unknown tool called without repo_path reports "'repo_path'" instead of Unknown tool

[cliffhall]

Problem

call_tool reads arguments["repo_path"] before dispatching on the tool name, so an unknown tool called without repo_path fails with the KeyError repr 'repo_path' instead of an "Unknown tool" error.

Where it is pinned

src/git/tests/test_protocol.py: test_unknown_tool_without_repo_path_reports_the_key_error, added in #4974 (Wave 1 of #4857). Each of these tests carries a KNOWN BUG marker: it asserts the current, wrong behavior, so the fix has to change it.

Expected

An unknown tool name returns "Unknown tool: " whatever arguments were sent.

Done when

• The behavior above is fixed, in the legacy-era (2025-11-25) server on SDK 1.x.
• The pinning tests assert the correct behavior, and their KNOWN BUG markers are gone.
• The per-file 90% coverage gate still passes.

[cliffhall]

Fixed by #5038, merged into v2/main (Wave 6 of #5004).