feat(derivatives): leverage, OI/volume, perpetual premium, funding APR, OI momentum (B16) (#214)

## B16 Derivatives — five new indicators (488 → 493)

All consume a `DerivativesTick` and emit `f64`:

| Indicator | Reads | Formula |
|-----------|-------|---------|
| `EstimatedLeverageRatio` | open_interest, long_size, short_size | `OI / (long + short)` |
| `OiToVolumeRatio` | open_interest, taker_buy_volume, taker_sell_volume | `OI / (buy + sell)` |
| `PerpetualPremiumIndex` | mark_price, index_price | `(mark − index) / index` |
| `FundingImpliedApr` | funding_rate | `rate × intervals_per_year` |
| `OpenInterestMomentum` | open_interest | `100 · (OI_t − OI_{t−period}) / OI_{t−period}` |

### Wiring
- Core structs + full unit tests (incl. zero-denominator branches).
- Hand-written Python/Node/WASM tick bindings; two new tick helpers (`deriv_oi_long_short`, `deriv_oi_taker`).
- Fuzz drives in `indicator_update_derivatives.rs`; dedicated reference + streaming-vs-batch tests (Python + Node).
- README counter + `docs/README.md` + `FAMILIES` assert bumped to 493.

### Verify (local, all green)
- `cargo test -p wickra-core --lib`: 4028 · `--doc`: 443
- clippy workspace: clean
- node: 563 · pytest: 928

bindings/node/__tests__/indicators.test.js

@@ -1443,6 +1443,56 @@ test('derivatives reject bad input', () => {
   assert.throws(() => new wickra.FundingBasis().update(100, 0));
 });
 
+test('B16 derivatives reference values', () => {
+  // Estimated leverage: oi / (long + short) = 200 / 100 = 2.
+  assert.ok(Math.abs(new wickra.EstimatedLeverageRatio().update(200, 60, 40) - 2.0) < 1e-12);
+  // OI-to-volume: oi / (buy + sell) = 100 / 50 = 2.
+  assert.ok(Math.abs(new wickra.OiToVolumeRatio().update(100, 30, 20) - 2.0) < 1e-12);
+  // Perpetual premium: (mark - index) / index = 0.5 / 100 = 0.005.
+  assert.ok(Math.abs(new wickra.PerpetualPremiumIndex().update(100.5, 100.0) - 0.005) < 1e-12);
+  // Funding-implied APR: rate * intervals = 0.0001 * 1095 = 0.1095.
+  assert.ok(Math.abs(new wickra.FundingImpliedApr(1095).update(0.0001) - 0.1095) < 1e-12);
+  // Open-interest momentum (period 2): warmup then ROC% = 100*(120 - 100)/100 = 20.
+  const oim = new wickra.OpenInterestMomentum(2);
+  assert.equal(oim.update(100), null);
+  assert.equal(oim.update(110), null);
+  assert.ok(Math.abs(oim.update(120) - 20.0) < 1e-12);
+});
+
+test('B16 derivatives streaming matches batch', () => {
+  const n = 30;
+  const oi = Array.from({ length: n }, (_, i) => 1000 + 50 * Math.sin(i * 0.3));
+  const longSz = Array.from({ length: n }, (_, i) => 600 + 20 * Math.cos(i * 0.2));
+  const shortSz = Array.from({ length: n }, (_, i) => 400 + 15 * Math.sin(i * 0.4));
+  const buy = Array.from({ length: n }, (_, i) => 300 + 10 * Math.sin(i * 0.5));
+  const sell = Array.from({ length: n }, (_, i) => 250 + 12 * Math.cos(i * 0.35));
+  const index = Array.from({ length: n }, (_, i) => 100 + Math.sin(i * 0.2));
+  const mark = Array.from({ length: n }, (_, i) => index[i] + 0.05 * Math.cos(i * 0.3));
+  const rate = Array.from({ length: n }, (_, i) => 0.0001 * Math.sin(i * 0.3));
+  const cmp = (batch, s, i) =>
+    assert.ok((s === null && Number.isNaN(batch[i])) || Math.abs(s - batch[i]) < 1e-12, `mismatch at ${i}`);
+
+  let b = new wickra.EstimatedLeverageRatio().batch(oi, longSz, shortSz);
+  let st = new wickra.EstimatedLeverageRatio();
+  for (let i = 0; i < n; i++) cmp(b, st.update(oi[i], longSz[i], shortSz[i]), i);
+
+  b = new wickra.OiToVolumeRatio().batch(oi, buy, sell);
+  st = new wickra.OiToVolumeRatio();
+  for (let i = 0; i < n; i++) cmp(b, st.update(oi[i], buy[i], sell[i]), i);
+
+  b = new wickra.PerpetualPremiumIndex().batch(mark, index);
+  st = new wickra.PerpetualPremiumIndex();
+  for (let i = 0; i < n; i++) cmp(b, st.update(mark[i], index[i]), i);
+
+  b = new wickra.FundingImpliedApr(1095).batch(rate);
+  st = new wickra.FundingImpliedApr(1095);
+  for (let i = 0; i < n; i++) cmp(b, st.update(rate[i]), i);
+
+  b = new wickra.OpenInterestMomentum(10).batch(oi);
+  st = new wickra.OpenInterestMomentum(10);
+  for (let i = 0; i < n; i++) cmp(b, st.update(oi[i]), i);
+});
+
 test('market breadth: AdvanceDecline reference values', () => {
   // A breadth tick is the universe as parallel arrays; the sign of `change`
   // classifies each symbol as advancing / declining / unchanged.

bindings/node/index.d.ts

@@ -4544,6 +4544,51 @@ export declare class CalendarSpread {
   isReady(): boolean
   warmupPeriod(): number
 }
+export type EstimatedLeverageRatioNode = EstimatedLeverageRatio
+export declare class EstimatedLeverageRatio {
+  constructor()
+  update(openInterest: number, longSize: number, shortSize: number): number | null
+  batch(openInterest: Array<number>, longSize: Array<number>, shortSize: Array<number>): Array<number>
+  reset(): void
+  isReady(): boolean
+  warmupPeriod(): number
+}
+export type OiToVolumeRatioNode = OiToVolumeRatio
+export declare class OiToVolumeRatio {
+  constructor()
+  update(openInterest: number, takerBuyVolume: number, takerSellVolume: number): number | null
+  batch(openInterest: Array<number>, takerBuyVolume: Array<number>, takerSellVolume: Array<number>): Array<number>
+  reset(): void
+  isReady(): boolean
+  warmupPeriod(): number
+}
+export type PerpetualPremiumIndexNode = PerpetualPremiumIndex
+export declare class PerpetualPremiumIndex {
+  constructor()
+  update(markPrice: number, indexPrice: number): number | null
+  batch(markPrice: Array<number>, indexPrice: Array<number>): Array<number>
+  reset(): void
+  isReady(): boolean
+  warmupPeriod(): number
+}
+export type FundingImpliedAprNode = FundingImpliedApr
+export declare class FundingImpliedApr {
+  constructor(intervalsPerYear: number)
+  update(fundingRate: number): number | null
+  batch(fundingRate: Array<number>): Array<number>
+  reset(): void
+  isReady(): boolean
+  warmupPeriod(): number
+}
+export type OpenInterestMomentumNode = OpenInterestMomentum
+export declare class OpenInterestMomentum {
+  constructor(period: number)
+  update(openInterest: number): number | null
+  batch(openInterest: Array<number>): Array<number>
+  reset(): void
+  isReady(): boolean
+  warmupPeriod(): number
+}
 export type AdvanceDeclineNode = AdvanceDecline
 export declare class AdvanceDecline {
   constructor()

bindings/node/src/lib.rs

@@ -14450,6 +14450,50 @@ fn deriv_taker(taker_buy_volume: f64, taker_sell_volume: f64) -> napi::Result<wc
     .map_err(map_err)
 }
 
+fn deriv_oi_long_short(
+    open_interest: f64,
+    long_size: f64,
+    short_size: f64,
+) -> napi::Result<wc::DerivativesTick> {
+    wc::DerivativesTick::new(
+        0.0,
+        1.0,
+        1.0,
+        1.0,
+        open_interest,
+        long_size,
+        short_size,
+        0.0,
+        0.0,
+        0.0,
+        0.0,
+        0,
+    )
+    .map_err(map_err)
+}
+
+fn deriv_oi_taker(
+    open_interest: f64,
+    taker_buy_volume: f64,
+    taker_sell_volume: f64,
+) -> napi::Result<wc::DerivativesTick> {
+    wc::DerivativesTick::new(
+        0.0,
+        1.0,
+        1.0,
+        1.0,
+        open_interest,
+        0.0,
+        0.0,
+        taker_buy_volume,
+        taker_sell_volume,
+        0.0,
+        0.0,
+        0,
+    )
+    .map_err(map_err)
+}
+
 fn deriv_liquidation(
     long_liquidation: f64,
     short_liquidation: f64,
@@ -15165,6 +15209,288 @@ impl CalendarSpreadNode {
     }
 }
 
+// Estimated leverage ratio: open interest over aggregate long+short size.
+#[napi(js_name = "EstimatedLeverageRatio")]
+pub struct EstimatedLeverageRatioNode {
+    inner: wc::EstimatedLeverageRatio,
+}
+
+impl Default for EstimatedLeverageRatioNode {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[napi]
+impl EstimatedLeverageRatioNode {
+    #[napi(constructor)]
+    pub fn new() -> Self {
+        Self {
+            inner: wc::EstimatedLeverageRatio::new(),
+        }
+    }
+    #[napi]
+    pub fn update(
+        &mut self,
+        open_interest: f64,
+        long_size: f64,
+        short_size: f64,
+    ) -> napi::Result<Option<f64>> {
+        Ok(self
+            .inner
+            .update(deriv_oi_long_short(open_interest, long_size, short_size)?))
+    }
+    #[napi]
+    pub fn batch(
+        &mut self,
+        open_interest: Vec<f64>,
+        long_size: Vec<f64>,
+        short_size: Vec<f64>,
+    ) -> napi::Result<Vec<f64>> {
+        if open_interest.len() != long_size.len() || long_size.len() != short_size.len() {
+            return Err(NapiError::from_reason(
+                "open_interest, long_size, short_size must be equal length".to_string(),
+            ));
+        }
+        let mut out = Vec::with_capacity(open_interest.len());
+        for i in 0..open_interest.len() {
+            out.push(
+                self.inner
+                    .update(deriv_oi_long_short(
+                        open_interest[i],
+                        long_size[i],
+                        short_size[i],
+                    )?)
+                    .unwrap_or(f64::NAN),
+            );
+        }
+        Ok(out)
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
+// OI-to-volume ratio: open interest over taker buy+sell volume.
+#[napi(js_name = "OiToVolumeRatio")]
+pub struct OiToVolumeRatioNode {
+    inner: wc::OiToVolumeRatio,
+}
+
+impl Default for OiToVolumeRatioNode {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[napi]
+impl OiToVolumeRatioNode {
+    #[napi(constructor)]
+    pub fn new() -> Self {
+        Self {
+            inner: wc::OiToVolumeRatio::new(),
+        }
+    }
+    #[napi]
+    pub fn update(
+        &mut self,
+        open_interest: f64,
+        taker_buy_volume: f64,
+        taker_sell_volume: f64,
+    ) -> napi::Result<Option<f64>> {
+        Ok(self.inner.update(deriv_oi_taker(
+            open_interest,
+            taker_buy_volume,
+            taker_sell_volume,
+        )?))
+    }
+    #[napi]
+    pub fn batch(
+        &mut self,
+        open_interest: Vec<f64>,
+        taker_buy_volume: Vec<f64>,
+        taker_sell_volume: Vec<f64>,
+    ) -> napi::Result<Vec<f64>> {
+        if open_interest.len() != taker_buy_volume.len()
+            || taker_buy_volume.len() != taker_sell_volume.len()
+        {
+            return Err(NapiError::from_reason(
+                "open_interest, taker_buy_volume, taker_sell_volume must be equal length"
+                    .to_string(),
+            ));
+        }
+        let mut out = Vec::with_capacity(open_interest.len());
+        for i in 0..open_interest.len() {
+            out.push(
+                self.inner
+                    .update(deriv_oi_taker(
+                        open_interest[i],
+                        taker_buy_volume[i],
+                        taker_sell_volume[i],
+                    )?)
+                    .unwrap_or(f64::NAN),
+            );
+        }
+        Ok(out)
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
+// Perpetual premium index: relative premium of mark over index price.
+#[napi(js_name = "PerpetualPremiumIndex")]
+pub struct PerpetualPremiumIndexNode {
+    inner: wc::PerpetualPremiumIndex,
+}
+
+impl Default for PerpetualPremiumIndexNode {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[napi]
+impl PerpetualPremiumIndexNode {
+    #[napi(constructor)]
+    pub fn new() -> Self {
+        Self {
+            inner: wc::PerpetualPremiumIndex::new(),
+        }
+    }
+    #[napi]
+    pub fn update(&mut self, mark_price: f64, index_price: f64) -> napi::Result<Option<f64>> {
+        Ok(self.inner.update(deriv_basis(mark_price, index_price)?))
+    }
+    #[napi]
+    pub fn batch(&mut self, mark_price: Vec<f64>, index_price: Vec<f64>) -> napi::Result<Vec<f64>> {
+        if mark_price.len() != index_price.len() {
+            return Err(NapiError::from_reason(
+                "mark_price and index_price must be equal length".to_string(),
+            ));
+        }
+        let mut out = Vec::with_capacity(mark_price.len());
+        for i in 0..mark_price.len() {
+            out.push(
+                self.inner
+                    .update(deriv_basis(mark_price[i], index_price[i])?)
+                    .unwrap_or(f64::NAN),
+            );
+        }
+        Ok(out)
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
+// Funding-implied APR: per-interval funding annualised.
+#[napi(js_name = "FundingImpliedApr")]
+pub struct FundingImpliedAprNode {
+    inner: wc::FundingImpliedApr,
+}
+
+#[napi]
+impl FundingImpliedAprNode {
+    #[napi(constructor)]
+    pub fn new(intervals_per_year: f64) -> napi::Result<Self> {
+        Ok(Self {
+            inner: wc::FundingImpliedApr::new(intervals_per_year).map_err(map_err)?,
+        })
+    }
+    #[napi]
+    pub fn update(&mut self, funding_rate: f64) -> napi::Result<Option<f64>> {
+        Ok(self.inner.update(deriv_funding(funding_rate)?))
+    }
+    #[napi]
+    pub fn batch(&mut self, funding_rate: Vec<f64>) -> napi::Result<Vec<f64>> {
+        let mut out = Vec::with_capacity(funding_rate.len());
+        for r in funding_rate {
+            out.push(self.inner.update(deriv_funding(r)?).unwrap_or(f64::NAN));
+        }
+        Ok(out)
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
+// Open-interest momentum: rate-of-change of open interest over a window.
+#[napi(js_name = "OpenInterestMomentum")]
+pub struct OpenInterestMomentumNode {
+    inner: wc::OpenInterestMomentum,
+}
+
+#[napi]
+impl OpenInterestMomentumNode {
+    #[napi(constructor)]
+    pub fn new(period: u32) -> napi::Result<Self> {
+        Ok(Self {
+            inner: wc::OpenInterestMomentum::new(period as usize).map_err(map_err)?,
+        })
+    }
+    #[napi]
+    pub fn update(&mut self, open_interest: f64) -> napi::Result<Option<f64>> {
+        Ok(self.inner.update(deriv_oi(open_interest)?))
+    }
+    #[napi]
+    pub fn batch(&mut self, open_interest: Vec<f64>) -> napi::Result<Vec<f64>> {
+        let mut out = Vec::with_capacity(open_interest.len());
+        for oi in open_interest {
+            out.push(self.inner.update(deriv_oi(oi)?).unwrap_or(f64::NAN));
+        }
+        Ok(out)
+    }
+    #[napi]
+    pub fn reset(&mut self) {
+        self.inner.reset();
+    }
+    #[napi(js_name = "isReady")]
+    pub fn is_ready(&self) -> bool {
+        self.inner.is_ready()
+    }
+    #[napi(js_name = "warmupPeriod")]
+    pub fn warmup_period(&self) -> u32 {
+        self.inner.warmup_period() as u32
+    }
+}
+
 // ---------- Market Breadth (CrossSection input) ----------
 //
 // A breadth tick is the per-symbol state of the whole universe, passed as four