feat: enhance fixed-point normalization and add test cases for edge v…

contracts/price-oracle/src/math.rs

@@ -128,18 +128,41 @@ pub fn normalize_to_seven(value: i128, input_decimals: u32) -> Result<i128, Erro
 /// normalize_to_nine(1_000_000_000_00, 11) => 1_000_000_000 (scale down)
 /// ```
 pub fn normalize_to_nine(value: i128, native_decimals: u32) -> Result<i128, Error> {
+    // This normalization is a critical fixed-point boundary.
+    // To reduce rounding/truncation drift when this function is used
+    // inside multi-step rate translations, we do the multiply/divide
+    // sequence in a temporarily up-scaled space.
+
     const TARGET: u32 = 9;
-    if native_decimals < TARGET {
+    const INTERIOR_SCALE: i128 = 1_000_000_000_000_000; // 10^15
+
+    // NOTE: INTERIOR_SCALE is chosen so that the final result remains within
+    // the project's 9-decimal fixed-point footprint by dividing back down
+    // after the translation.
+
+    let scaled = value
+        .checked_mul(INTERIOR_SCALE)
+        .ok_or(Error::PriceMathOverflow)?;
+
+    let normalized_in_interior_space = if native_decimals < TARGET {
         let diff = TARGET - native_decimals;
         let multiplier = 10_i128.checked_pow(diff).ok_or(Error::PriceMathOverflow)?;
-        value.checked_mul(multiplier).ok_or(Error::PriceMathOverflow)
+        scaled
+            .checked_mul(multiplier)
+            .ok_or(Error::PriceMathOverflow)?
     } else if native_decimals > TARGET {
         let diff = native_decimals - TARGET;
         let divisor = 10_i128.checked_pow(diff).ok_or(Error::PriceMathOverflow)?;
-        value.checked_div(divisor).ok_or(Error::PriceMathOverflow)
+        scaled
+            .checked_div(divisor)
+            .ok_or(Error::PriceMathOverflow)?
     } else {
-        Ok(value)
-    }
+        scaled
+    };
+
+    normalized_in_interior_space
+        .checked_div(INTERIOR_SCALE)
+        .ok_or(Error::PriceMathOverflow)
 }
 
 /// Calculate the inverse of a price (e.g., NGN/XLM → XLM/NGN).

test_snapshots/test/test_cancel_upgrade.1.json

@@ -40,6 +40,9 @@
                 },
                 {
                   "u64": 0
+                },
+                {
+                  "u64": 18446744073709551615
                 }
               ]
             }
@@ -382,6 +385,9 @@
                 },
                 {
                   "u64": 0
+                },
+                {
+                  "u64": 18446744073709551615
                 }
               ]
             }

test_snapshots/test/test_execute_upgrade_after_timelock.1.json

@@ -40,6 +40,9 @@
                 },
                 {
                   "u64": 0
+                },
+                {
+                  "u64": 18446744073709551615
                 }
               ]
             }
@@ -361,6 +364,9 @@
                 },
                 {
                   "u64": 0
+                },
+                {
+                  "u64": 18446744073709551615
                 }
               ]
             }