just use seperate transaction handlers

TODO.md

@@ -53,7 +53,8 @@ Goal: "aws cli works reliably for CreateTable/ListTables/PutItem/GetItem/DeleteI
 ### 5) UpdateItem / conditional logic groundwork
 - [x] `UpdateItem` handler registered in router (currently returns clear "not yet supported" error)
 - [x] Implement `UpdateItem` (initially minimal: SET for scalar attrs)
-  - [ ] `UpdateItem` needs UPDATED_NEW/UPDATED_OLD response filtering for perfect parity with Dynamo
+  - [x] `UpdateItem` needs UPDATED_NEW/UPDATED_OLD response filtering for perfect parity with Dynamo
+    - **DONE**: `filter_updated_attributes` extracts modified paths from `Update_Plan` and filters the response item to only include those attributes. `get_update_plan_modified_paths` + `filter_item_to_paths` in `transact.odin`.
 - [x] Add `ConditionExpression` support for Put/Delete/Update (start with simple comparisons)
 - [x] Define internal "update plan" representation (parsed ops → applied mutations)
 
@@ -83,7 +84,13 @@ These align with the "Future Enhancements" list in ARCHITECTURE.md.
 ### 9) Batch + transactions
 - [x] BatchWriteItem
 - [x] BatchGetItem
-- [ ] Transactions (TransactWriteItems / TransactGetItems)
+- [x] Transactions (TransactWriteItems / TransactGetItems)
+  - **DONE**: `transact.odin` implements all-or-nothing semantics:
+    - Put, Delete, Update, ConditionCheck action types
+    - Pre-flight condition evaluation (all conditions checked before any mutation)
+    - Deterministic table lock ordering to prevent deadlocks
+    - `transact_handlers.odin` contains HTTP handlers and JSON parsing
+    - TransactGetItems supports ProjectionExpression per item
 
 ### 10) Performance / ops
 - [ ] Connection reuse / keep-alive tuning
@@ -105,4 +112,4 @@ These align with the "Future Enhancements" list in ARCHITECTURE.md.
 - [x] Fix TODO hygiene: keep this file short and "actionable"
   - Added "Bug Fixes Applied" section documenting what changed and why
 - [ ] Add a CONTRIBUTING quick checklist (allocator rules, formatting, tests)
-- [ ] Add "known limitations" section in README (unsupported DynamoDB features)
+- [ ] Add "known limitations" section in README (unsupported DynamoDB features)