Step 549: add cost reduction suggestion engine

progress.md

@@ -9550,3 +9550,40 @@ decision flow.
 - **Steps completed:** 5
 - **New tests in phase plan:** 56/56 passing
 - **Routing/context/cost optimization integration:** PASS
+
+### Step 549: Suggestion Engine for Cost Reductions
+**Status:** PASS (12/12 tests)
+
+Implements cost-reduction suggestion generation for constrained orchestration,
+including template substitution, batching, and context narrowing opportunities
+with priority and savings estimates.
+
+**Files added:**
+- `editor/src/CostReductionSuggestionEngine.h` - cost suggestion module:
+  - emits template substitution recommendations when deterministic paths exist
+  - emits batching recommendations for compatible multi-op workloads
+  - emits context narrowing recommendations for wide symbol candidate sets
+  - computes estimated token savings and priority by budget pressure
+  - deterministic sorting by priority and estimated savings
+- `editor/tests/step549_test.cpp` - 12 tests covering:
+  - suggestion emission behavior per optimization path
+  - no-suggestion baseline behavior
+  - over-budget priority amplification behavior
+  - savings scaling behavior by op/symbol breadth
+  - path eligibility thresholds for batching/context narrowing
+  - ordering/tiebreak behavior
+  - rationale presence requirements
+
+**Files modified:**
+- `editor/CMakeLists.txt` - `step549_test` target
+
+**Verification run:**
+- `cmake -S editor -B editor/build-native` - PASS
+- `cmake --build editor/build-native --target step549_test step548_test` - PASS
+- `./editor/build-native/step549_test` - PASS (12/12)
+- `./editor/build-native/step548_test` - PASS (8/8) regression coverage
+
+**Architecture gate check:**
+- `editor/src/CostReductionSuggestionEngine.h` within header-size limit (`68` <= `600`)
+- `editor/tests/step549_test.cpp` within test-file size guidance (`146` lines)
+- Header-only architecture and naming conventions remain aligned with `ARCHITECTURE.md`