fix(stablecoin): preserve clamped accrual progress

programs/stablecoin/src/generate_debt.rs

@@ -16,7 +16,7 @@ use crate::shared::{
 /// Mints stablecoin debt against an existing position.
 ///
 /// # Panics
-/// Panics if the position is not authorized, the oracle is stale, or the post-mint position would
+/// Panics if the owner is not authorized, the oracle is stale, or the post-mint position would
 /// be undercollateralized.
 #[expect(
     clippy::too_many_arguments,

programs/stablecoin/src/shared.rs

@@ -7,7 +7,7 @@ use nssa_core::{
 use stablecoin_core::{
     compute_protocol_parameters_pda, compute_redemption_price_state_pda,
     compute_stability_fee_accumulator_pda, current_accumulated_rate, ProtocolParameters,
-    RedemptionPriceState, StabilityFeeAccumulator,
+    RedemptionPriceState, StabilityFeeAccumulator, MAXIMUM_COMPOUNDING_WINDOW_MILLISECONDS,
 };
 
 pub(crate) fn read_clock_timestamp(clock: &AccountWithMetadata) -> u64 {
@@ -84,9 +84,17 @@ pub(crate) fn accrue_stability_fee_state(
     params: &ProtocolParameters,
     now: u64,
 ) -> StabilityFeeAccumulator {
+    let elapsed = now
+        .saturating_sub(accumulator.last_accrued_at)
+        .min(MAXIMUM_COMPOUNDING_WINDOW_MILLISECONDS);
+    let last_accrued_at = accumulator
+        .last_accrued_at
+        .checked_add(elapsed)
+        .expect("Clamped elapsed timestamp cannot overflow");
+
     StabilityFeeAccumulator {
         accumulated_rate_at_last_accrual: current_accumulated_rate(accumulator, params, now),
-        last_accrued_at: now,
+        last_accrued_at,
     }
 }
 

programs/stablecoin/src/tests.rs

@@ -685,7 +685,7 @@ fn accrue_stability_fee_clamps_elapsed_window() {
     );
     assert_eq!(
         updated.last_accrued_at,
-        MAXIMUM_COMPOUNDING_WINDOW_MILLISECONDS + 1
+        MAXIMUM_COMPOUNDING_WINDOW_MILLISECONDS
     );
 }