Add Quasar port of the order-book (CLOB) example

finance/order-book/quasar/Cargo.toml

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+[package]
+name = "quasar-order-book"
+version = "0.1.0"
+edition = "2021"
+
+# Standalone workspace - not part of the root program-examples workspace.
+# Quasar uses a different resolver and dependency tree.
+[workspace]
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = [
+    'cfg(target_os, values("solana"))',
+]
+
+[lib]
+crate-type = ["cdylib", "lib"]
+
+[features]
+alloc = []
+client = []
+debug = []
+
+[dependencies]
+# quasar pin rationale: matches the finance/escrow Quasar example. master HEAD
+# currently fails to compile because zeropod 0.3.x auto-generates accessor
+# methods that conflict with hand-written ones in quasar-spl. 623bb70 is the
+# last working rev on master before that bump. Unpin (back to branch = "master")
+# once upstream merges the fix.
+quasar-lang = { git = "https://github.com/blueshift-gg/quasar", rev = "623bb70" }
+quasar-spl = { git = "https://github.com/blueshift-gg/quasar", rev = "623bb70" }
+solana-address = { version = "2.2.0" }
+solana-instruction = { version = "3.2.0" }
+# The ported Openbook slab casts a contiguous byte region to fixed-layout node
+# structs. `derive` gives `Pod`/`Zeroable`; `min_const_generics` lets the
+# 1024-slot `[AnyNode; N]` array derive `Pod` without hitting bytemuck's
+# default 32-element array cap.
+bytemuck = { version = "1.18", features = ["derive", "min_const_generics"] }
+# Compile-time slab-layout asserts (node size, alignment), matching upstream.
+static_assertions = "1.1"
+
+[dev-dependencies]
+quasar-svm = { git = "https://github.com/blueshift-gg/quasar-svm" }
+spl-token-interface = { version = "2.0.0" }
+solana-program-pack = { version = "3.1.0" }

finance/order-book/quasar/Quasar.toml

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+[project]
+name = "quasar_order_book"
+
+[toolchain]
+type = "solana"
+
+[testing]
+language = "rust"
+
+[testing.rust]
+framework = "quasar-svm"
+
+[testing.rust.test]
+program = "cargo"
+args = [
+    "test",
+    "tests::",
+]
+
+[clients]
+path = "target/client"
+languages = ["rust"]

finance/order-book/quasar/README.md

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+# Order Book — Central Limit Order Book (CLOB), Quasar port
+
+A [central limit order book (CLOB)](https://www.investopedia.com/terms/l/limitorderbook.asp) — the market
+structure NYSE, NASDAQ, CME, and onchain venues like Phoenix and OpenBook run on. Users post buy or sell
+offers at prices they pick; the program matches crossing offers in **price-time priority** and settles the
+resulting token movements.
+
+This is a [Quasar](https://github.com/blueshift-gg/quasar) port of the Anchor example in
+[`../anchor`](../anchor). Quasar is a zero-copy, `no_std`, zero-allocation Solana framework with Anchor-like
+syntax (`#[program]`, `#[derive(Accounts)]`, `#[account]`) that compiles to a much smaller binary. Both builds
+use the **same program ID** (`C69UJ8irfmHq5ysyLek7FKApHR86FBeupiz4JnoyPzzx`), so offchain tooling and PDA
+derivations work against either unchanged. The Anchor README carries the full conceptual walkthrough; this one
+focuses on how the program works and what the Quasar port does differently.
+
+## What the program does
+
+Two users want to swap tokens at prices they each chose. **Alice** holds USDC (the *quote* mint — the pricing
+unit) and wants to buy NVDAx (the *base* mint — the asset being priced), but only at 900 USDC/share or lower.
+**Bob** holds NVDAx and will sell at 900 or higher. They post a **bid** and an **ask**; when the prices cross,
+the program fills them.
+
+- The party whose order **rests** on the book first is the **maker**.
+- The party whose order arrives and **crosses** the resting order is the **taker**.
+
+A fill always clears at the **maker's** posted price (standard CLOB rule): the taker gets price improvement
+versus their own limit. The taker pays a fee (in basis points) routed to a fee vault; the maker's proceeds are
+credited net of that fee.
+
+Funds are held in **program-owned vaults** (the market PDA is their token authority) from the moment an order
+locks them until settlement. There is no admin escape hatch — the market authority can only withdraw
+accumulated **fees**, never user balances. The deployed program bytecode is the only thing that can move vault
+funds, and it moves them only along the place / cancel / settle paths below.
+
+## Accounts and PDAs
+
+| Account | Kind | Seeds | Role |
+| --- | --- | --- | --- |
+| `Market` | PDA | `["market", base_mint, quote_mint]` | One trading pair. Stores config + vault addresses. Its PDA is the vaults' token authority. |
+| `OrderBook` | keypair account | — (not a PDA) | Two critbit slabs (bids + asks), ~180 KB. Zero-copy. Bound to its market by the market's stored `order_book`. |
+| `MarketUser` | PDA | `["market_user", market, owner]` | Per-user, per-market. Tracks open order ids and `unsettled_*` balances owed back to the user. |
+| `Order` | PDA | `["order", market, order_id]` | One order. `order_id` is the book's monotonic counter at placement time. |
+| `base_vault` / `quote_vault` | token accounts | — | Hold locked funds while orders are open. Market PDA is the authority. |
+| `fee_vault` | token account | — | Accumulates taker fees (quote mint). Kept separate so user balances and fees can't be confused. |
+
+The order book is **not** a PDA. Solana caps inner-CPI account allocations at 10 KB, so a ~180 KB account can't
+be created with an `init` constraint — the client calls `system_program::create_account` directly (sizing it to
+`ORDER_BOOK_ACCOUNT_SIZE`, program-owned, zeroed) and passes it to `initialize_market`, which verifies and
+initializes it in place.
+
+## The two-lot pricing model
+
+Both sides of the book are denominated in **lots**, mirroring Serum/OpenBook, so `price` and `quantity` read
+as human numbers regardless of each mint's decimals:
+
+```
+raw_base  = quantity × base_lot_size
+raw_quote = quantity × price × quote_lot_size
+```
+
+Choose `base_lot_size = 10^max(d_base − d_quote, 0)` and `quote_lot_size = 10^max(d_quote − d_base, 0)`. For
+NVDAx (9 decimals) / USDC (6 decimals): `base_lot_size = 1000`, `quote_lot_size = 1`, so `price = 100` means
+100 USDC-units per base lot and `tick_size = 1` is one atomic increment.
+
+## Instruction lifecycle
+
+| Handler | What it does |
+| --- | --- |
+| `initialize_market` | Create the `Market` PDA, the two vaults, and the fee vault; initialize the pre-created order-book account. |
+| `create_market_user` | Create a caller's `MarketUser` for a market. |
+| `place_order` | Lock funds, cross the opposing side in price-time priority, credit fills to maker/taker `unsettled_*`, route the taker fee, and rest any remainder. |
+| `cancel_order` | Credit an open order's locked remainder back to the owner's `unsettled_*` and remove it from the book. |
+| `settle_funds` | Move a user's `unsettled_*` balances out of the vaults into their token accounts. |
+| `withdraw_fees` | Authority-only: drain the fee vault to the authority's token account. |
+
+`place_order` takes `side` (`0` = bid, `1` = ask), `price`, `quantity`, and `order_id`. The caller passes the
+resting maker orders to cross as **remaining accounts**, in pairs of `(maker_order, maker_market_user)`, in the
+book's price-time priority. `order_id` must equal the book's current `next_order_id` (the program verifies it),
+so the client derives the `Order` PDA deterministically.
+
+Fills never transfer tokens directly to the counterparty — they credit `unsettled_*` balances that each user
+drains later via `settle_funds`. This keeps the per-fill account footprint small (no maker ATAs in the fill
+path), as in OpenBook v2.
+
+## The matching engine
+
+Each side of the book is a **critbit tree** (radix trie) ported from
+[openbook-v2](https://github.com/openbook-dex/openbook-v2) (MIT; see `src/state/slab/LICENSE-OPENBOOK`). Leaves
+carry the resting order's price, remaining quantity, owner, and id; a 128-bit key packs `[price][seq_num]` so an
+in-order walk yields best-price-first, and within a price level the sequence number preserves time priority.
+Insert, remove, and best-price lookup are all sub-linear, so matching stays cheap as depth grows.
+
+## What the Quasar port does differently
+
+The trading logic, fee model, lot math, and matching engine are identical to the Anchor build. The differences
+are all consequences of Quasar being zero-copy, `no_std`, and zero-allocation:
+
+- **The order book is accessed by casting raw account bytes.** Anchor uses `AccountLoader<OrderBook>`; Quasar
+  has no `AccountLoader`, so `initialize_market` / `place_order` / `cancel_order` cast the account's byte region
+  to `&mut OrderBook` with `bytemuck` (an 8-byte discriminator guards against a wrong account). The slab code is
+  otherwise a near-verbatim port.
+- **`MarketUser.open_orders` is a fixed `[u8; 160]` (20 packed u64s) plus a length**, not a borsh `Vec<u64>`. A
+  resizable field would make the account dynamic, which is awkward to mutate on the maker side where the account
+  arrives as a remaining account. The fixed buffer keeps every mutation an in-place write.
+- **The slab is heap-free.** Its transient traversal stack is a fixed array (a critbit tree over 128-bit keys is
+  at most 128 nodes deep), and two write-only stacks the upstream carried were dropped. A single `place_order`
+  crosses at most `MAX_FILLS` (16) resting orders; any remainder rests on the book for a later order to cross.
+- **`side` and order status/side enums are stored as `u8`** (zero-copy accounts hold POD scalars). The `u8`
+  wire encoding of `side` matches the Anchor build's borsh enum discriminant.
+
+## Safety and custody
+
+- Every vault transfer out is signed by the **market PDA** via `invoke_signed`; only the deployed program can
+  move locked funds.
+- `settle_funds` zeroes a user's `unsettled_*` **before** transferring (checks-effects-interactions), so no
+  token-hook re-entry could double-withdraw.
+- `place_order` binds every market-owned account (`base_vault`, `quote_vault`, `fee_vault`, both mints, the
+  order book) to the addresses stored on the `Market` PDA with `has_one`, so a caller can't substitute the fee
+  vault for a user vault and drain fees.
+- Taker fees use **ceiling** division, rounding in the protocol's favor so many tiny fills can't leak a minor
+  unit to the maker.
+
+## Building and testing
+
+Requires the [Solana toolchain](https://docs.anza.xyz/cli/install) (for `cargo build-sbf`) and the
+[Quasar CLI](https://github.com/blueshift-gg/quasar):
+
+```sh
+cargo install --git https://github.com/blueshift-gg/quasar quasar-cli --locked
+quasar build          # compiles the program to target/deploy/quasar_order_book.so
+cargo test            # QuasarSVM integration tests (they load the compiled .so)
+```
+
+`quasar build` must run before `cargo test`: the tests load the compiled `.so` into
+[QuasarSVM](https://github.com/blueshift-gg/quasar-svm), an in-process SVM, via `include`/`fs::read`. The suite
+in `src/tests.rs` drives the full lifecycle — initialize a market, create users, rest an ask, cross it with a
+bid, settle both sides, and withdraw the fee — asserting on-chain state, token balances, and fee accounting at
+each step, plus an authorization rejection.
+
+## Extending
+
+- **Self-trade prevention:** reject or cancel-back when a taker would cross their own resting order.
+- **Post-only / IOC / FOK** order types by gating the rest-vs-cancel behaviour on a flag.
+- **Multiple fee tiers** keyed on the taker's `MarketUser`.
+- **Market pause/resume** by flipping `Market.is_active` from an authority-gated handler.

finance/order-book/quasar/src/errors.rs

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+use quasar_lang::prelude::*;
+
+/// Program errors. `#[error_code]` assigns the numeric codes and generates the
+/// `From<OrderBookError> for ProgramError` conversion that `?` and `require!`
+/// rely on. Codes start at 6000, matching Anchor's custom-error base so the two
+/// builds report the same numbers to clients.
+#[error_code]
+pub enum OrderBookError {
+    InvalidPrice = 6000,
+    OrderNotFound,
+    MarketPaused,
+    Unauthorized,
+    OrderBookFull,
+    TooManyOpenOrders,
+    InvalidTickSize,
+    InvalidBaseLotSize,
+    InvalidQuoteLotSize,
+    BelowMinOrderSize,
+    OrderNotCancellable,
+    NumericalOverflow,
+    InvalidFeeBasisPoints,
+    InvalidFeeVault,
+    InvalidBaseVault,
+    InvalidQuoteVault,
+    InvalidBaseMint,
+    InvalidQuoteMint,
+    MakerAccountMismatch,
+    MissingMakerAccounts,
+    MakerOwnerMismatch,
+    NotMarketAuthority,
+    InvalidOrderBook,
+    InvalidOrderBookOwner,
+    OrderBookAlreadyInitialized,
+    OrderIdMismatch,
+    InvalidSide,
+}

finance/order-book/quasar/src/instructions/admin/mod.rs

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+pub mod withdraw_fees;
+
+pub use withdraw_fees::*;

finance/order-book/quasar/src/instructions/admin/withdraw_fees.rs

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+use quasar_lang::prelude::*;
+use quasar_spl::prelude::*;
+
+use crate::errors::OrderBookError;
+use crate::state::{Market, MARKET_SEED};
+
+/// Drain the market's accumulated taker fees into the authority's token
+/// account. Authority-only - arbitrary callers must not be able to siphon the
+/// fee vault. Transfers the current balance of the fee vault in full.
+#[derive(Accounts)]
+pub struct WithdrawFeesAccountConstraints {
+    #[account(has_one(fee_vault) @ OrderBookError::InvalidFeeVault)]
+    pub market: Account<Market>,
+
+    #[account(mut)]
+    pub fee_vault: Account<Token>,
+
+    #[account(mut)]
+    pub authority_quote_account: Account<Token>,
+
+    pub quote_mint: Account<Mint>,
+
+    pub authority: Signer,
+
+    pub token_program: Program<TokenProgram>,
+}
+
+#[inline(always)]
+pub fn handle_withdraw_fees(
+    accounts: &mut WithdrawFeesAccountConstraints,
+) -> Result<(), ProgramError> {
+    require_keys_eq!(
+        *accounts.authority.address(),
+        accounts.market.authority,
+        OrderBookError::NotMarketAuthority
+    );
+
+    let fee_balance = accounts.fee_vault.amount();
+    if fee_balance == 0 {
+        // Nothing to do - exit quietly rather than failing, so this
+        // instruction is safe to call on a cron/heartbeat even when there
+        // haven't been any fills since the last run.
+        return Ok(());
+    }
+
+    let base_mint = accounts.market.base_mint;
+    let quote_mint = accounts.market.quote_mint;
+    let bump = [accounts.market.bump];
+    let seeds = [
+        Seed::from(MARKET_SEED),
+        Seed::from(base_mint.as_ref()),
+        Seed::from(quote_mint.as_ref()),
+        Seed::from(bump.as_ref()),
+    ];
+
+    accounts
+        .token_program
+        .transfer_checked(
+            &accounts.fee_vault,
+            &accounts.quote_mint,
+            &accounts.authority_quote_account,
+            &accounts.market,
+            fee_balance,
+            accounts.quote_mint.decimals,
+        )
+        .invoke_signed(&seeds)?;
+
+    Ok(())
+}