Summary

• wrap nullclaw agent CLI streaming output with the existing streaming.TagFilter so raw <tool_call>...</tool_call> blocks do not leak into foreground terminal output
• add a regression test covering streamed tool-call suppression in src/agent/cli.zig
• retain and free MCP stdio child environment maps in src/mcp.zig to fix the repository-wide leak surfaced by zig build test --summary all

Why

• streamed provider deltas in the CLI path were written directly to stdout, unlike daemon/channel streaming paths that already strip tool-control markup
• the full local validation required by AGENTS.md exposed an unrelated MCP env leak in the test suite, so this PR includes the minimal ownership fix needed to keep the suite green

Validation

• zig build
• zig build -Doptimize=ReleaseSmall
• zig build test --summary all

Notes

• this change is focused to the CLI streaming presentation path; tool execution behavior is unchanged
• unrelated untracked workspace files were left untouched