feat(context): enhance timeout handling, tenant isolation, and budget management

- Added timeout enforcement for token counting, scoring, and compression with detailed error handling.
- Introduced tenant isolation in context caching using project and agent identifiers.
- Enhanced budget management with stricter checks for critical context overspending and buffer limitations.
- Optimized per-context locking with cleanup to prevent memory leaks in concurrent environments.
- Updated default assembly timeout settings for improved performance and reliability.
- Improved XML escaping in Claude adapter for safety against injection attacks.
- Standardized token estimation using model-specific ratios.

backend/app/services/context/engine.py

@@ -212,7 +212,10 @@ class ContextEngine:
         # Check cache if enabled
         fingerprint: str | None = None
         if use_cache and self._cache.is_enabled:
-            fingerprint = self._cache.compute_fingerprint(contexts, query, model)
+            # Include project_id and agent_id for tenant isolation
+            fingerprint = self._cache.compute_fingerprint(
+                contexts, query, model, project_id=project_id, agent_id=agent_id
+            )
             cached = await self._cache.get_assembled(fingerprint)
             if cached:
                 logger.debug(f"Cache hit for context assembly: {fingerprint}")