refactor: consolidate call hierarchy tools into single unified tool

[BumpyClock]

Summary

The current LSP-MCP server exposes 3 separate call hierarchy tools that could be consolidated into a single, more intuitive tool.

Current State

Three separate tools:

1. prepare_call_hierarchy

   • Returns call hierarchy items at a position
   • This is an intermediate LSP call - not useful standalone
   • Requires follow-up with incoming_calls or outgoing_calls

2. incoming_calls

   • Finds functions that call the function at position
   • Requires internal handling of prepare_call_hierarchy first

3. outgoing_calls

   • Finds functions called by the function at position
   • Also requires prepare_call_hierarchy internally

Problems:

1. prepare_call_hierarchy is useless alone - An LLM has to know to call incoming_calls or outgoing_calls afterward
2. Three tools for one concept - Adds cognitive overhead and tool list bloat
3. Inconsistent with other tools - No other LSP feature is split across multiple tools like this

Proposed Change

Consolidate into a single call_graph tool:

#[tool(description = "Find incoming/outgoing function calls at a position")]
async fn call_graph(
    &self,
    path: String,
    line: u32,
    character: u32,
    direction: String,  // "incoming" | "outgoing" | "both"
    include_raw_response: Option<bool>,
) -> ToolOutput

Usage examples:

// Find what calls this function
{"path": "src/mcp.rs", "line": 32, "character": 13, "direction": "incoming"}

// Find what this function calls
{"path": "src/mcp.rs", "line": 32, "character": 13, "direction": "outgoing"}

// Get full call graph (both directions)
{"path": "src/mcp.rs", "line": 32, "character": 13, "direction": "both"}

Response format:

{
  "function": {
    "name": "definitions_in_file",
    "location": {"path": "src/mcp.rs", "line": 32, "character": 13}
  },
  "incoming_calls": [...],  // present if direction is "incoming" or "both"
  "outgoing_calls": [...]   // present if direction is "outgoing" or "both"
}

Implementation Notes

• Internally, call_graph would still call prepare_call_hierarchy first
• The consolidation is purely at the MCP tool interface level
• Backwards compatibility: Keep old tools available but remove from presets

Impact

• Reduces tool count by 2 (3 tools → 1 tool)
• Simpler mental model for LLM agents
• More intuitive API - one tool for call relationships
• Optional "both" direction enables richer analysis in single call

Related

• Full tool analysis: .ai_agents/tool_review.md
• Issue feat: reduce output noise in find_references and definitions_in_file #138: Output noise improvements