feat: context assembly -- per-task context packaging via MCP (OPE-172)

backend/dependencies.py

@@ -11,6 +11,7 @@
 from services.dependency_analyzer import DependencyAnalyzer
 from services.style_analyzer import StyleAnalyzer
 from services.dna_extractor import DNAExtractor
+from services.context_assembler import ContextAssembler
 from services.rate_limiter import RateLimiter, APIKeyManager
 from services.supabase_service import get_supabase_service
 from services.input_validator import CostController
@@ -25,6 +26,7 @@
 dependency_analyzer = DependencyAnalyzer()
 style_analyzer = StyleAnalyzer()
 dna_extractor = DNAExtractor()
+context_assembler = ContextAssembler()
 
 # Rate limiting and API key management
 rate_limiter = RateLimiter(redis_client=cache.redis if cache.redis else None)

backend/main.py

@@ -35,6 +35,7 @@
 from routes.github import router as github_router
 from routes.feedback import router as feedback_router
 from routes.admin import router as admin_router
+from routes.context import router as context_router
 from routes.ws_playground import websocket_playground_index
 from routes.ws_repos import websocket_repo_indexing
 
@@ -106,6 +107,7 @@ async def dispatch(self, request: Request, call_next):
 app.include_router(github_router, prefix=API_PREFIX)
 app.include_router(feedback_router, prefix=API_PREFIX)
 app.include_router(admin_router, prefix=API_PREFIX)
+app.include_router(context_router, prefix=API_PREFIX)
 
 # WebSocket endpoints (versioned)
 app.add_api_websocket_route(f"{API_PREFIX}/ws/index/{{repo_id}}", websocket_index)

backend/routes/context.py

@@ -0,0 +1,81 @@
+"""Context assembly endpoint.
+
+Provides per-task context packaging via POST /api/v1/context/assemble.
+Uses semantic search + dependency graph + project rules to build a
+minimal, precise context package for AI coding assistants.
+"""
+import time
+from typing import Any
+
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel, Field
+
+from dependencies import verify_repo_access
+from middleware.auth import AuthContext, require_auth
+from services.observability import (
+    add_breadcrumb,
+    capture_exception,
+    logger,
+    metrics,
+    set_operation_context,
+)
+
+router = APIRouter(tags=["context"])
+
+
+class AssembleRequest(BaseModel):
+    task: str = Field(..., min_length=3, max_length=1000)
+    repo_id: str
+    token_budget: int = Field(default=1500, ge=100, le=10000)
+
+
+@router.post("/context/assemble")
+async def assemble_context(
+    request: AssembleRequest,
+    auth: AuthContext = Depends(require_auth),
+) -> dict[str, Any]:
+    """Assemble task-specific context from semantic search + deps + rules.
+
+    Returns a markdown context package sized to fit within token_budget,
+    containing only the files, dependencies, and project rules relevant
+    to the given task description.
+    """
+    set_operation_context(
+        "context_assemble",
+        user_id=auth.user_id,
+        repo_id=request.repo_id,
+    )
+    add_breadcrumb("Context assembly requested", category="context", repo_id=request.repo_id)
+
+    verify_repo_access(request.repo_id, auth.user_id)
+
+    from dependencies import context_assembler
+
+    start = time.time()
+    try:
+        result = await context_assembler.assemble(
+            task=request.task,
+            repo_id=request.repo_id,
+            user_id=auth.user_id,
+            token_budget=request.token_budget,
+        )
+
+        elapsed = time.time() - start
+        logger.info(
+            "Context assembled",
+            repo_id=request.repo_id,
+            files=result["files_found"],
+            tokens=result["tokens_used"],
+            budget=request.token_budget,
+            duration_ms=round(elapsed * 1000),
+        )
+        metrics.timing("context_assemble_ms", elapsed * 1000)
+
+        return result
+
+    except HTTPException:
+        raise
+    except Exception as exc:
+        capture_exception(exc, operation="context_assemble", repo_id=request.repo_id)
+        logger.error("Context assembly failed: %s", exc)
+        raise HTTPException(status_code=500, detail="Context assembly failed")