Fix unsafe non-null assertions in Map operations

- deduplication.ts: Replace signatureMap.get(signature)! with safe optional chaining
- supersede-writes.ts: Replace writesByFile.get() and readsByFile.get() with safe optional chaining

Prevents potential runtime errors from Map state inconsistencies.

Author: mister-test

lib/strategies/deduplication.ts

@@ -57,7 +57,10 @@ export const deduplicate = (
         if (!signatureMap.has(signature)) {
             signatureMap.set(signature, [])
         }
-        signatureMap.get(signature)!.push(id)
+        const ids = signatureMap.get(signature)
+        if (ids) {
+            ids.push(id)
+        }
     }
 
     // Find duplicates - keep only the most recent (last) in each group

lib/strategies/supersede-writes.ts

@@ -61,12 +61,18 @@ export const supersedeWrites = (
             if (!writesByFile.has(filePath)) {
                 writesByFile.set(filePath, [])
             }
-            writesByFile.get(filePath)!.push({ id, index: i })
+            const writes = writesByFile.get(filePath)
+            if (writes) {
+                writes.push({ id, index: i })
+            }
         } else if (metadata.tool === "read") {
             if (!readsByFile.has(filePath)) {
                 readsByFile.set(filePath, [])
             }
-            readsByFile.get(filePath)!.push(i)
+            const reads = readsByFile.get(filePath)
+            if (reads) {
+                reads.push(i)
+            }
         }
     }