fix: configure biome to allow any in public APIs

- Follow sdk-kit pattern: any is intentional for public APIs
- Set noExplicitAny to 'warn' globally
- Disable for types.ts and runtime.ts (public API surfaces)
- Disable for test files
- Update documentation to explain any usage pattern
- Keep any for config values, event payloads, custom user data

Author: prosdev

.cursorrules

@@ -61,6 +61,16 @@ If we build something generic that could benefit other sdk-kit users, design it
 - Prefer pure functions for testability
 - Extract logic into pure functions when possible
 
+#### Use of `any`
+Following sdk-kit's pattern, `any` is intentionally used in **public API surfaces** only:
+- **Public API files** (types.ts, runtime.ts): `any` allowed for flexibility
+  - Config values, event payloads, custom user data
+  - Provides better developer experience
+- **Internal implementation**: Avoid `any`, use specific types
+- **Test files**: `any` allowed for mocks/fixtures
+- **Biome config**: `noExplicitAny` set to `"warn"` globally, `"off"` for specific files
+- This is a conscious trade-off: type safety vs. API flexibility
+
 ### Testing
 - Unit tests for all functionality
 - >80% coverage minimum

CLAUDE.md

@@ -151,15 +151,23 @@ interface Decision {
 - ✅ Extract testable pure functions
 - ✅ Include acceptance criteria in commits
 - ✅ Use sdk-kit capabilities where available
+- ✅ Use `any` intentionally in public APIs (like sdk-kit does)
 
 **DON'T:**
 - ❌ Commit without running tests and linter
 - ❌ Skip type definitions for public APIs
 - ❌ Build what already exists in sdk-kit
 - ❌ Create complex stateful classes when pure functions suffice
-- ❌ Use `any` in public APIs
+- ❌ Use `any` in internal implementation (only in public APIs)
 - ❌ Commit changes without updating relevant specs
 
+**About `any` Types:**
+Following sdk-kit's pattern, `any` is intentionally used in public API files (types.ts) for:
+- Config values, event payloads, custom user data
+- Better developer experience and API flexibility
+- Biome configured to allow `any` in specific files only
+- Internal implementation should use specific types
+
 ## Project Structure
 
 ```

biome.json

@@ -9,13 +9,38 @@
         "noUnusedVariables": "error"
       },
       "suspicious": {
-        "noExplicitAny": "error"
+        "noExplicitAny": "warn"
       },
       "style": {
         "useConst": "error"
       }
     }
   },
+  "overrides": [
+    {
+      "includes": ["**/*.test.ts", "**/*.spec.ts"],
+      "linter": {
+        "rules": {
+          "suspicious": {
+            "noExplicitAny": "off"
+          }
+        }
+      }
+    },
+    {
+      "includes": [
+        "packages/core/src/types.ts",
+        "packages/core/src/runtime.ts"
+      ],
+      "linter": {
+        "rules": {
+          "suspicious": {
+            "noExplicitAny": "off"
+          }
+        }
+      }
+    }
+  ],
   "formatter": {
     "enabled": true,
     "indentWidth": 2,