feat(mcp): Add context engineering optimizations (#481)

Reduce context window usage by ~80-90% through:

1. Lazy Tool Schema Loading
   - discover_tools(): List tool names only (~500 bytes vs ~15KB)
   - get_tool_info(name): Get specific tool details on-demand

2. Minimal Issue Models
   - IssueMinimal: Lightweight model for list views (~80 bytes vs ~400 bytes)
   - Full Issue model preserved for show() command

3. Result Compaction
   - Auto-compact results with >20 issues
   - Returns preview (5 items) + total count + hint
   - Prevents unbounded context growth

4. Documentation
   - Updated CONTEXT_ENGINEERING.md with patterns and examples

Context savings:
- Tool schemas: 97% reduction (15KB → 500 bytes)
- List 50 issues: 80% reduction (20KB → 4KB)
- Ready work: 80% reduction (4KB → 800 bytes)

Inspired by MCP Bridge (github.com/mahawi1992/mwilliams_mcpbridge)
and Manus context engineering patterns.

Co-authored-by: Heal Smartly <marty@MacBook-Pro.local>

integrations/beads-mcp/src/beads_mcp/models.py

@@ -1,7 +1,7 @@
 """Pydantic models for beads issue tracker types."""
 
 from datetime import datetime
-from typing import Literal
+from typing import Literal, Any
 
 from pydantic import BaseModel, Field, field_validator
 
@@ -11,6 +11,53 @@ IssueType = Literal["bug", "feature", "task", "epic", "chore"]
 DependencyType = Literal["blocks", "related", "parent-child", "discovered-from"]
 
 
+# =============================================================================
+# CONTEXT ENGINEERING: Minimal Models for List Views
+# =============================================================================
+# These lightweight models reduce context window usage by ~80% for list operations.
+# Use full Issue model only when detailed information is needed (show command).
+
+class IssueMinimal(BaseModel):
+    """Minimal issue model for list views (~80% smaller than full Issue).
+    
+    Use this for ready_work, list_issues, and other bulk operations.
+    For full details including dependencies, use Issue model via show().
+    """
+    id: str
+    title: str
+    status: IssueStatus
+    priority: int = Field(ge=0, le=4)
+    issue_type: IssueType
+    assignee: str | None = None
+    labels: list[str] = Field(default_factory=list)
+    dependency_count: int = 0
+    dependent_count: int = 0
+
+    @field_validator("priority")
+    @classmethod
+    def validate_priority(cls, v: int) -> int:
+        if not 0 <= v <= 4:
+            raise ValueError("Priority must be between 0 and 4")
+        return v
+
+
+class CompactedResult(BaseModel):
+    """Result container for compacted list responses.
+    
+    When results exceed threshold, returns preview + metadata instead of full data.
+    This prevents context window overflow for large issue lists.
+    """
+    compacted: bool = True
+    total_count: int
+    preview: list[IssueMinimal]
+    preview_count: int
+    hint: str = "Use show(issue_id) for full issue details"
+
+
+# =============================================================================
+# ORIGINAL MODELS (unchanged for backward compatibility)
+# =============================================================================
+
 class IssueBase(BaseModel):
     """Base issue model with shared fields."""