feat: add LSP Call Hierarchy support to Living Canvas

[cxxxr]

Summary

Add multi-language call graph visualization to Living Canvas using the LSP Call Hierarchy API.

• New: call-graph-lsp package - Lem-independent LSP to call-graph conversion
• New: lsp-provider.lisp - Async analysis with idle timers (UI-responsive)
• New: lsp-call-hierarchy.lisp - LSP request wrappers
• New: json-format.lisp - JSON serialization for call-graph

Architecture

┌─────────────────────────────────────┐
│  User Commands                      │
│  M-x living-canvas-lsp              │
│  M-x living-canvas-lsp-full         │
│  M-x living-canvas-lsp-cancel       │
└──────────────┬──────────────────────┘
               │
               ▼
┌─────────────────────────────────────┐
│  lem-living-canvas                  │
│  lsp-provider.lisp                  │
│  (idle timer-based async analysis)  │
└──────────────┬──────────────────────┘
               │
               ▼
┌─────────────────────────────────────┐
│  call-graph-lsp (Lem-independent)   │
│  LSP → call-graph conversion        │
└──────────────┬──────────────────────┘
               │
               ▼
┌─────────────────────────────────────┐
│  Language Server (gopls, etc.)      │
│  textDocument/prepareCallHierarchy  │
│  callHierarchy/incomingCalls        │
│  callHierarchy/outgoingCalls        │
└─────────────────────────────────────┘

Motivation

1. Multi-language support: Works with any LSP server supporting Call Hierarchy (Go, TypeScript, Rust, etc.)
2. UI-responsive: Idle timer-based processing prevents editor freeze during analysis
3. Clean separation: call-graph-lsp has no Lem dependencies (only LSP protocol definitions)

Changes

File	Description
extensions/call-graph-lsp/	New package: LSP→call-graph conversion
extensions/call-graph/json-format.lisp	New: JSON serialization
extensions/living-canvas/lsp-call-hierarchy.lisp	New: LSP request wrappers
extensions/living-canvas/lsp-provider.lisp	New: Async analysis provider
extensions/living-canvas/living-canvas.lisp	New commands: living-canvas-lsp, etc.

Test Plan

• Unit tests pass (call-graph/tests, call-graph-lsp/tests, lem-living-canvas/tests)
• M-x living-canvas-lsp works with Go files (gopls)
• M-x living-canvas-lsp-full shows incoming + outgoing calls
• M-x living-canvas-lsp-cancel aborts running analysis
• Progress messages update during analysis
• UI remains responsive during large file analysis

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AI Usage Disclosure

Did you use LLMs/AI tools for this PR?

• No, this is 100% human-authored.
• Yes, AI-assisted (Human-led logic, AI-assisted implementation).
• Yes, AI-generated (Logic primarily derived from prompt/vibe).

Tooling Used: Claude Code (Claude Opus 4.5)

---

The "Human-in-the-Loop" Verification

1. Logic Walkthrough

The LSP Call Hierarchy integration follows a three-layer architecture:

1. call-graph-lsp layer: Pure conversion functions from LSP protocol objects to call-graph structures. No Lem dependencies, only uses lem-lsp-base/protocol-3-17 for type definitions.

2. lsp-call-hierarchy layer: Lem-specific LSP request wrappers. Handles buffer→workspace lookup, capability checking, and LSP method invocation.

3. lsp-provider layer: Orchestrates async analysis using idle timers. Key design decisions:

   • LSP requests must run on main thread (not thread-safe in Lem)
   • Idle timer processes symbols in batches (*lsp-batch-size* = 5)
   • Yields between batches to keep UI responsive
   • Exponential backoff retry for failed requests

2. Reviewer's Guide

High-risk areas:

• lsp-provider.lisp:261-266: Error handling in async batch processing
• lsp-provider.lisp:110-123: Retry with backoff logic
• Uses internal Lem LSP mode APIs (lem-lsp-mode/lsp-mode::buffer-workspace)

Suggested focus:

• Verify idle timer cleanup on cancellation (lsp-async-cleanup)
• Check edge cases: empty buffer, LSP server disconnect mid-analysis
• Validate node ID uniqueness for overloaded functions