Use canonical ContextStream MCP identity in Buzz agents

[escott-]

Summary

• expose ContextStream to Buzz ACP under the canonical contextstream server name
• document the real headless Claude permission boundary
• add a least-privilege project-local permission example and regression coverage

Why

A genuine Claude Code run in Buzz showed that Buzz derives MCP names from the command basename. The raw contextstream-mcp basename produces a noncanonical tool prefix, so the launcher now uses a private executable alias named contextstream. The same run confirmed that Buzz headless read/write sessions need an explicit reviewed Claude allowlist in addition to accept-edits mode.

Verification

• npm test (9/9)
• bash -n run-agent.sh
• JSON parse checks for settings and compatibility records
• run-agent.sh --check --runtime claude against the real local fixture
• git diff --check