docs+code: rename "rent" to "lease fee" throughout asset-leasing

"Rent" collides with Solana's account-rent concept. Switching to
"lease fee" makes the per-second payment from lessee to lessor
unambiguous.

Also tightens the README:

- Drops the "this README is a teaching document" / "It is not a
  deployed, audited production program" / "treat it as a learning
  example" framing — true of every program in program-examples by
  definition.
- Drops the disambiguation disclaimer about Solana account rent vs
  lease rent (no longer needed once the per-second payment is named
  the lease fee).
- Drops fungibility caveats around what the lessee returns — just
  says they return leased_amount of leased_mint.
- Switches "neutral escrow" to "non-custodial escrow".
- Adds a concrete xNVDA / USDC worked example with both rallying-
  and falling-NVIDIA scenarios so the asymmetric-payoff (short-like)
  shape of the lessee position is explicit.
- Adds §4.3 (falling-price path) covering the case where the
  leased asset depreciates and the lessee benefits.

Code rename details:

- Field: Lease.rent_per_second -> Lease.lease_fee_per_second
- Field: Lease.last_rent_paid_ts -> Lease.last_paid_ts
- Function: compute_rent_due -> compute_lease_fee_due
- Instruction: pay_rent -> pay_lease_fee (module / handler /
  Accounts struct / source filename)
- Error: InvalidRentPerSecond -> InvalidLeaseFeePerSecond
- Local variables and code comments updated to match.
- Solana terminology kept verbatim where it really means
  account rent (rent-exempt lamports, Sysvar<Rent>,
  sysvar::rent::ID, rent_epoch, etc.).

The Quasar port is renamed in lockstep so the two implementations
stay byte-for-byte identical at the IDL level (same discriminators,
same Lease layout). Quasar's tests are renamed to match.

All 11 LiteSVM tests pass after the rename. Quasar `quasar build`
also succeeds.

Author: Edward (OpenClaw)

defi/asset-leasing/anchor/README.md

@@ -10,8 +10,8 @@ pub enum AssetLeasingError {
     InvalidLeasedAmount,
     #[msg("Required collateral amount must be greater than zero")]
     InvalidCollateralAmount,
-    #[msg("Rent per second must be greater than zero")]
-    InvalidRentPerSecond,
+    #[msg("Lease fee per second must be greater than zero")]
+    InvalidLeaseFeePerSecond,
     #[msg("Maintenance margin is outside the allowed range")]
     InvalidMaintenanceMargin,
     #[msg("Liquidation bounty is outside the allowed range")]

defi/asset-leasing/anchor/programs/asset-leasing/src/errors.rs

@@ -8,7 +8,7 @@ use crate::{
     constants::{COLLATERAL_VAULT_SEED, LEASED_VAULT_SEED, LEASE_SEED},
     errors::AssetLeasingError,
     instructions::{
-        pay_rent::update_last_paid_ts,
+        pay_lease_fee::update_last_paid_ts,
         shared::{close_vault, transfer_tokens_from_vault},
     },
     state::{Lease, LeaseStatus},
@@ -155,20 +155,20 @@ pub fn handle_close_expired(context: Context<CloseExpired>) -> Result<()> {
         &[collateral_vault_seeds],
     )?;
 
-    // Settle rent accounting on the default path.
+    // Settle lease-fee accounting on the default path.
     //
-    // We are not forwarding any accrued rent to the lessor here — on default
+    // We are not forwarding any accrued lease fees to the lessor here — on default
     // the lessor takes the whole collateral vault as compensation — but we
-    // still bump \`last_rent_paid_ts\` so the invariant
-    // \`last_rent_paid_ts <= now.min(end_ts)\` stays intact. That matters for
+    // still bump \`last_paid_ts\` so the invariant
+    // \`last_paid_ts <= now.min(end_ts)\` stays intact. That matters for
     // any future version of the program that wants to split the collateral
-    // differently (pro-rata rent, partial refund on default, haircut to the
+    // differently (pro-rata lease fees, partial refund on default, haircut to the
     // lessee for unused time): such a version can read
-    // \`last_rent_paid_ts\` and trust that everything up to \`now\` is already
+    // \`last_paid_ts\` and trust that everything up to \`now\` is already
     // settled, rather than having to reason about whether this branch ever
     // bumped the timestamp.
     //
-    // No-op on the \`Listed\` branch because rent never started accruing.
+    // No-op on the \`Listed\` branch because Lease fees never started accruing.
     if status == LeaseStatus::Active {
         update_last_paid_ts(&mut context.accounts.lease, now);
     }

defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/close_expired.rs

@@ -75,15 +75,15 @@ pub fn handle_create_lease(
     lease_id: u64,
     leased_amount: u64,
     required_collateral_amount: u64,
-    rent_per_second: u64,
+    lease_fee_per_second: u64,
     duration_seconds: i64,
     maintenance_margin_bps: u16,
     liquidation_bounty_bps: u16,
     feed_id: [u8; 32],
 ) -> Result<()> {
     // Reject leased_mint == collateral_mint. Allowing both to be the same
     // mint would collapse the two vaults' seed derivations into one shared
-    // token-balance pool, making rent-vs-collateral accounting ambiguous and
+    // token-balance pool, making lease-fee-vs-collateral accounting ambiguous and
     // enabling griefing paths where the lessee's "collateral" is the same
     // asset they already hold as the lease principal.
     require!(
@@ -96,7 +96,7 @@ pub fn handle_create_lease(
         required_collateral_amount > 0,
         AssetLeasingError::InvalidCollateralAmount
     );
-    require!(rent_per_second > 0, AssetLeasingError::InvalidRentPerSecond);
+    require!(lease_fee_per_second > 0, AssetLeasingError::InvalidLeaseFeePerSecond);
     require!(duration_seconds > 0, AssetLeasingError::InvalidDuration);
     require!(
         maintenance_margin_bps > 0 && maintenance_margin_bps <= MAX_MAINTENANCE_MARGIN_BPS,
@@ -131,13 +131,13 @@ pub fn handle_create_lease(
         // No collateral yet — posted on take_lease.
         collateral_amount: 0,
         required_collateral_amount,
-        rent_per_second,
+        lease_fee_per_second,
         duration_seconds,
-        // start_ts / end_ts / last_rent_paid_ts are set when the lease
+        // start_ts / end_ts / last_paid_ts are set when the lease
         // activates in `take_lease`.
         start_ts: 0,
         end_ts: 0,
-        last_rent_paid_ts: 0,
+        last_paid_ts: 0,
         maintenance_margin_bps,
         liquidation_bounty_bps,
         feed_id,

defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/create_lease.rs

@@ -11,7 +11,7 @@ use crate::{
     },
     errors::AssetLeasingError,
     instructions::{
-        pay_rent::compute_rent_due,
+        pay_lease_fee::compute_lease_fee_due,
         shared::{close_vault, transfer_tokens_from_vault},
     },
     state::{Lease, LeaseStatus},
@@ -34,7 +34,7 @@ pub struct Liquidate<'info> {
     #[account(mut)]
     pub keeper: Signer<'info>,
 
-    /// CHECK: PDA seed + rent/collateral destination.
+    /// CHECK: PDA seed + lease-fee / collateral destination.
     #[account(mut)]
     pub lessor: UncheckedAccount<'info>,
 
@@ -174,10 +174,10 @@ pub fn handle_liquidate(context: Context<Liquidate>) -> Result<()> {
         AssetLeasingError::PositionHealthy
     );
 
-    // Settle accrued rent first (up to end_ts) so the lessor is paid for the
+    // Settle accrued lease fees first (up to end_ts) so the lessor is paid for the
     // time the lessee actually used. Only then slice off bounty + remainder.
-    let rent_due = compute_rent_due(&context.accounts.lease, now)?;
-    let rent_payable = rent_due.min(context.accounts.lease.collateral_amount);
+    let lease_fee_due = compute_lease_fee_due(&context.accounts.lease, now)?;
+    let lease_fee_payable = lease_fee_due.min(context.accounts.lease.collateral_amount);
 
     let lease_key = context.accounts.lease.key();
     let collateral_vault_bump = context.accounts.lease.collateral_vault_bump;
@@ -193,11 +193,11 @@ pub fn handle_liquidate(context: Context<Liquidate>) -> Result<()> {
         core::slice::from_ref(&leased_vault_bump),
     ];
 
-    if rent_payable > 0 {
+    if lease_fee_payable > 0 {
         transfer_tokens_from_vault(
             &context.accounts.collateral_vault,
             &context.accounts.lessor_collateral_account,
-            rent_payable,
+            lease_fee_payable,
             &context.accounts.collateral_mint,
             &context.accounts.collateral_vault.to_account_info(),
             &context.accounts.token_program,
@@ -209,10 +209,10 @@ pub fn handle_liquidate(context: Context<Liquidate>) -> Result<()> {
         .accounts
         .lease
         .collateral_amount
-        .checked_sub(rent_payable)
+        .checked_sub(lease_fee_payable)
         .ok_or(AssetLeasingError::MathOverflow)?;
 
-    // Bounty is a percentage of the collateral *after* rent — guarantees we
+    // Bounty is a percentage of the collateral *after* lease fees — guarantees we
     // never try to pay out more than what actually sits in the vault.
     let bounty = (remaining as u128)
         .checked_mul(context.accounts.lease.liquidation_bounty_bps as u128)
@@ -264,7 +264,7 @@ pub fn handle_liquidate(context: Context<Liquidate>) -> Result<()> {
     )?;
 
     context.accounts.lease.collateral_amount = 0;
-    context.accounts.lease.last_rent_paid_ts = now.min(context.accounts.lease.end_ts);
+    context.accounts.lease.last_paid_ts = now.min(context.accounts.lease.end_ts);
     context.accounts.lease.status = LeaseStatus::Liquidated;
 
     Ok(())

defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/liquidate.rs

@@ -1,7 +1,7 @@
 pub mod close_expired;
 pub mod create_lease;
 pub mod liquidate;
-pub mod pay_rent;
+pub mod pay_lease_fee;
 pub mod return_lease;
 pub mod shared;
 pub mod take_lease;
@@ -10,7 +10,7 @@ pub mod top_up_collateral;
 pub use close_expired::*;
 pub use create_lease::*;
 pub use liquidate::*;
-pub use pay_rent::*;
+pub use pay_lease_fee::*;
 pub use return_lease::*;
 pub use shared::*;
 pub use take_lease::*;

defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/mod.rs

@@ -12,9 +12,9 @@ use crate::{
 };
 
 #[derive(Accounts)]
-pub struct PayRent<'info> {
-    /// Anyone may settle rent — the lessee has every incentive to keep the
-    /// lease current, but a keeper bot could also push a payment before a
+pub struct PayLeaseFee<'info> {
+    /// Anyone may settle the lease fee — the lessee has every incentive to keep the
+    /// lease current, but a keeper bot could also push a lease fee payment before a
     /// liquidation check so healthy leases stay healthy.
     #[account(mut)]
     pub payer: Signer<'info>,
@@ -45,7 +45,7 @@ pub struct PayRent<'info> {
     pub collateral_vault: Box<InterfaceAccount<'info, TokenAccount>>,
 
     /// Lessor's collateral-mint ATA, created on demand so the lessor does not
-    /// need to pre-fund it with rent.
+    /// need to pre-fund it with the lease fee.
     #[account(
         init_if_needed,
         payer = payer,
@@ -60,21 +60,21 @@ pub struct PayRent<'info> {
     pub system_program: Program<'info, System>,
 }
 
-pub fn handle_pay_rent(context: Context<PayRent>) -> Result<()> {
+pub fn handle_pay_lease_fee(context: Context<PayLeaseFee>) -> Result<()> {
     let now = Clock::get()?.unix_timestamp;
 
-    let rent_amount = compute_rent_due(&context.accounts.lease, now)?;
+    let lease_fee_amount = compute_lease_fee_due(&context.accounts.lease, now)?;
 
     // No time has passed (or already capped at end_ts). Nothing to do.
-    if rent_amount == 0 {
+    if lease_fee_amount == 0 {
         update_last_paid_ts(&mut context.accounts.lease, now);
         return Ok(());
     }
 
-    // Cap rent at whatever collateral actually sits in the vault. If the
+    // Cap lease fees at whatever collateral actually sits in the vault. If the
     // lessee under-collateralised we cannot magically create funds; the
     // remainder is their debt and can trigger liquidation.
-    let payable = rent_amount.min(context.accounts.collateral_amount_available());
+    let payable = lease_fee_amount.min(context.accounts.collateral_amount_available());
 
     if payable > 0 {
         let lease_key = context.accounts.lease.key();
@@ -108,27 +108,27 @@ pub fn handle_pay_rent(context: Context<PayRent>) -> Result<()> {
     Ok(())
 }
 
-/// Rent accrues linearly: `(min(now, end_ts) - last_rent_paid_ts) * rate`.
+/// Lease fee accrues linearly: `(min(now, end_ts) - last_paid_ts) * rate`.
 /// Extracted so it can be re-used by `return_lease` and `liquidate` for a
 /// final settlement before closing the lease.
-pub fn compute_rent_due(lease: &Lease, now: i64) -> Result<u64> {
+pub fn compute_lease_fee_due(lease: &Lease, now: i64) -> Result<u64> {
     let cutoff = now.min(lease.end_ts);
-    if cutoff <= lease.last_rent_paid_ts {
+    if cutoff <= lease.last_paid_ts {
         return Ok(0);
     }
-    let elapsed = (cutoff - lease.last_rent_paid_ts) as u64;
+    let elapsed = (cutoff - lease.last_paid_ts) as u64;
     elapsed
-        .checked_mul(lease.rent_per_second)
+        .checked_mul(lease.lease_fee_per_second)
         .ok_or(AssetLeasingError::MathOverflow.into())
 }
 
-/// Advance `last_rent_paid_ts` but never past the lease end — after end_ts
-/// the lease is settled and extra rent does not accrue.
+/// Advance `last_paid_ts` but never past the lease end — after end_ts
+/// the lease is settled and extra Lease fees do not accrue.
 pub fn update_last_paid_ts(lease: &mut Lease, now: i64) {
-    lease.last_rent_paid_ts = now.min(lease.end_ts);
+    lease.last_paid_ts = now.min(lease.end_ts);
 }
 
-impl<'info> PayRent<'info> {
+impl<'info> PayLeaseFee<'info> {
     fn collateral_amount_available(&self) -> u64 {
         self.lease.collateral_amount
     }

…set-leasing/src/instructions/pay_rent.rs …easing/src/instructions/pay_lease_fee.rsdefi/asset-leasing/anchor/programs/asset-leasing/src/instructions/pay_rent.rs renamed to defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/pay_lease_fee.rs defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/pay_rent.rs renamed to defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/pay_lease_fee.rs

@@ -8,7 +8,7 @@ use crate::{
     constants::{COLLATERAL_VAULT_SEED, LEASED_VAULT_SEED, LEASE_SEED},
     errors::AssetLeasingError,
     instructions::{
-        pay_rent::{compute_rent_due, update_last_paid_ts},
+        pay_lease_fee::{compute_lease_fee_due, update_last_paid_ts},
         shared::{close_vault, transfer_tokens_from_user, transfer_tokens_from_vault},
     },
     state::{Lease, LeaseStatus},
@@ -19,7 +19,7 @@ pub struct ReturnLease<'info> {
     #[account(mut)]
     pub lessee: Signer<'info>,
 
-    /// CHECK: Reference only — receives rent + closed-vault rent refund.
+    /// CHECK: Reference only — receives the lease fee + closed-vault rent-exempt-lamport refund.
     #[account(mut)]
     pub lessor: UncheckedAccount<'info>,
 
@@ -40,7 +40,7 @@ pub struct ReturnLease<'info> {
     pub collateral_mint: Box<InterfaceAccount<'info, Mint>>,
 
     /// Leased tokens flow back into this vault from the lessee, then out to
-    /// the lessor in the same instruction. Closed at the end to reclaim rent.
+    /// the lessor in the same instruction. Closed at the end to reclaim rent-exempt lamports.
     #[account(
         mut,
         seeds = [LEASED_VAULT_SEED, lease.key().as_ref()],
@@ -134,9 +134,9 @@ pub fn handle_return_lease(context: Context<ReturnLease>) -> Result<()> {
         &[leased_vault_seeds],
     )?;
 
-    // 3. Settle accrued rent: collateral vault -> lessor.
-    let rent_due = compute_rent_due(&context.accounts.lease, now)?;
-    let rent_payable = rent_due.min(context.accounts.lease.collateral_amount);
+    // 3. Settle accrued lease fees: collateral vault -> lessor.
+    let lease_fee_due = compute_lease_fee_due(&context.accounts.lease, now)?;
+    let lease_fee_payable = lease_fee_due.min(context.accounts.lease.collateral_amount);
 
     let collateral_vault_bump = context.accounts.lease.collateral_vault_bump;
     let collateral_vault_seeds: &[&[u8]] = &[
@@ -145,11 +145,11 @@ pub fn handle_return_lease(context: Context<ReturnLease>) -> Result<()> {
         core::slice::from_ref(&collateral_vault_bump),
     ];
 
-    if rent_payable > 0 {
+    if lease_fee_payable > 0 {
         transfer_tokens_from_vault(
             &context.accounts.collateral_vault,
             &context.accounts.lessor_collateral_account,
-            rent_payable,
+            lease_fee_payable,
             &context.accounts.collateral_mint,
             &context.accounts.collateral_vault.to_account_info(),
             &context.accounts.token_program,
@@ -158,20 +158,20 @@ pub fn handle_return_lease(context: Context<ReturnLease>) -> Result<()> {
     }
 
     // 4. Refund remaining collateral to the lessee. Returning early does not
-    // entitle the lessee to a future-rent refund — rent only accrues for time
-    // actually used, so `compute_rent_due` already excludes the unused tail.
-    let collateral_after_rent = context
+    // entitle the lessee to a future-lease-fee refund — Lease fees only accrue for time
+    // actually used, so `compute_lease_fee_due` already excludes the unused tail.
+    let collateral_after_lease_fees = context
         .accounts
         .lease
         .collateral_amount
-        .checked_sub(rent_payable)
+        .checked_sub(lease_fee_payable)
         .ok_or(AssetLeasingError::MathOverflow)?;
 
-    if collateral_after_rent > 0 {
+    if collateral_after_lease_fees > 0 {
         transfer_tokens_from_vault(
             &context.accounts.collateral_vault,
             &context.accounts.lessee_collateral_account,
-            collateral_after_rent,
+            collateral_after_lease_fees,
             &context.accounts.collateral_mint,
             &context.accounts.collateral_vault.to_account_info(),
             &context.accounts.token_program,

defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/return_lease.rs

@@ -127,7 +127,7 @@ pub fn handle_take_lease(context: Context<TakeLease>) -> Result<()> {
     lease.collateral_amount = required_collateral_amount;
     lease.start_ts = now;
     lease.end_ts = end_ts;
-    lease.last_rent_paid_ts = now;
+    lease.last_paid_ts = now;
     lease.status = LeaseStatus::Active;
 
     Ok(())

defi/asset-leasing/anchor/programs/asset-leasing/src/instructions/take_lease.rs

@@ -23,7 +23,7 @@ pub mod asset_leasing {
         lease_id: u64,
         leased_amount: u64,
         required_collateral_amount: u64,
-        rent_per_second: u64,
+        lease_fee_per_second: u64,
         duration_seconds: i64,
         maintenance_margin_bps: u16,
         liquidation_bounty_bps: u16,
@@ -34,7 +34,7 @@ pub mod asset_leasing {
             lease_id,
             leased_amount,
             required_collateral_amount,
-            rent_per_second,
+            lease_fee_per_second,
             duration_seconds,
             maintenance_margin_bps,
             liquidation_bounty_bps,
@@ -48,18 +48,18 @@ pub mod asset_leasing {
         instructions::take_lease::handle_take_lease(context)
     }
 
-    /// Stream rent from the collateral vault to the lessor, up to `end_ts`.
+    /// Stream the lease fee from the collateral vault to the lessor, up to `end_ts`.
     /// Anyone may call this to keep the lease current.
-    pub fn pay_rent(context: Context<PayRent>) -> Result<()> {
-        instructions::pay_rent::handle_pay_rent(context)
+    pub fn pay_lease_fee(context: Context<PayLeaseFee>) -> Result<()> {
+        instructions::pay_lease_fee::handle_pay_lease_fee(context)
     }
 
     /// Lessee adds more collateral to stay above the maintenance margin.
     pub fn top_up_collateral(context: Context<TopUpCollateral>, amount: u64) -> Result<()> {
         instructions::top_up_collateral::handle_top_up_collateral(context, amount)
     }
 
-    /// Lessee returns the leased tokens (at or before `end_ts`). Accrued rent
+    /// Lessee returns the leased tokens (at or before `end_ts`). Accrued lease fees
     /// is settled and the remaining collateral is refunded.
     pub fn return_lease(context: Context<ReturnLease>) -> Result<()> {
         instructions::return_lease::handle_return_lease(context)