Phase 7: TUI + MCP Client for tri-api

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Summary

Interactive terminal (TUI) + MCP stdio client for tri-api.

7A: TUI (~200 LOC)

src/tri-api/tui.zig — ANSI colored output, prompt input, streaming chars, status bar.

tri-api                        # No args → interactive TUI mode
tri-api "one-shot prompt"      # With args → batch mode (unchanged)

Interactive: tri> prompt, colored tool/assistant output, /quit to exit.

7B: MCP Client (~150 LOC)

src/tri-api/mcp_client.zig — stdio subprocess transport, JSON-RPC 2.0.

Config in .tri-api/settings.json:

{
  "mcp_servers": {
    "trinity": { "command": ["./zig-out/bin/trinity-mcp"] }
  }
}

On startup: spawn servers → listTools() → merge into Anthropic tool_definitions.

Files

File	Action	LOC
src/tri-api/tui.zig	NEW	~200
src/tri-api/mcp_client.zig	NEW	~150
src/tri-api/main.zig	MOD	~+60
src/tri-api/tool_executor.zig	MOD	~+30

Acceptance Criteria

• tri-api with no args enters interactive TUI mode
• ANSI colored output (cyan assistant, yellow tool, red error)
• MCP servers spawn from settings.json config
• MCP tools merged into Anthropic API tool_definitions
• MCP tool_use calls routed to mcp_client.callTool()
• zig build clean

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Implemented in beb4d44. Phase 7 complete:

• tui.zig (195 LOC): Interactive TUI with ANSI colors, tri> prompt, /quit, /sessions
• mcp_client.zig (356 LOC): MCP stdio client with JSON-RPC 2.0 subprocess transport
• main.zig (+145 LOC): Interactive mode (no args), batch mode (with args), MCP loading
• tool_executor.zig (+38 LOC): executeDynamic routes to built-in or MCP tools
• tool_protocol.zig (+7 LOC): extractFieldFrom, composable writeToolDefinitions

Build clean, 12/12 tests pass, all formatted.