[TASK] Post-merge polish for remote fuzz (#232) — errors, transport, copy, docs

[hello-args]

Summary

Post-merge follow-up for merged #232 (remote mcts fuzz --url). The feature shipped; this issue tracks the review items that were deferred from the initial merge.

Assignee: @biswajit-satapathy1998

Problem

#232 landed remote protocol fuzz via --url for HTTP/SSE endpoints (closes GAP-190). Maintainer review on the PR identified four polish items to complete on main in a follow-up PR.

Expected Behavior

See acceptance criteria and recommendation.

References

• Merged PR: feat(fuzz): add remote protocol fuzz via --url for HTTP/SSE endpoints #232
• GAP-190 in docs/more/feature-expansion-plan.md
• Related: [BUG] Fix crash when probing remote MCP servers over streamable HTTP #148 (streamable-http client API — separate P0; fuzz may share http_session patterns)

Acceptance Criteria

• mcts fuzz --url <bad-host> → exit 2, no traceback
• --transport behavior matches docs (SSE wired or explicitly streamable-http-only with warning)
• Remote 5xx findings do not mention "subprocess exited"
• CHANGELOG.md updated
• Docs no longer list GAP-190 / remote fuzz as "Planned" or "Missing"
• Tests pass; add/adjust tests if copy or transport guard changes