chain: wire IIR4 generator (RT_IIR4_GEN) + add chain smoke test

- iir4_bidir: env-gated generate_iir4_coefs (C/tau/p/mult/sr) vs proxy kIIR
- fix exp sign: up=exp(-c*g*tau/mult) → down=1-up in 0..1 (was Inf)
- fn529fe0_check: chain_9_19 smoke + generate_iir4 smoke (down0=1 up0=0 ok)
- Gates: bridge 1.594, structural 2.689 (RT_CASC=0) unchanged

dsp/fn529fe0.cpp

@@ -196,13 +196,35 @@ void cascade_detect(
 
 static inline void iir4_bidir_340510(float* x, size_t nbin) {
     // BLOCKMAP:52af09 IIR4×2 bidir log-domain base 0x340510
-    // Uses DOUBLE precision (movsd/mulsd in disasm)
+    // Uses DOUBLE precision (movsd/mulsd/cvtpd2ps in disasm 1191-1201)
-    // Coefficients from FUN_180533340 generator (frequency-dependent warp)
+    // When RT_IIR4_GEN=1, generate via FUN_180533340 (freq-warp g=fc_norm/i|pow), else use proxy kIIR_A1/B1
-    // For now, use kIIR_A1/B1 as proxy (structure is correct)
+    static std::vector<double> genDown, genUp;
+    static int genN = 0;
+    const double* A1;
+    const double* B1;
+    const double* A2;
+    const double* B2;
+    static const int useGen = getenv("RT_IIR4_GEN") ? atoi(getenv("RT_IIR4_GEN")) : 0;
+    if (useGen) {
+        if ((int)nbin != genN) {
+            genDown.assign(nbin, 0.0); genUp.assign(nbin, 0.0);
+            double C = getenv("RT_IIR4_C") ? atof(getenv("RT_IIR4_C")) : 1000.0;
+            double tau = getenv("RT_IIR4_TAU") ? atof(getenv("RT_IIR4_TAU")) : 1200.0;
+            double p = getenv("RT_IIR4_P") ? atof(getenv("RT_IIR4_P")) : 0.5;
+            double mult = getenv("RT_IIR4_MULT") ? atof(getenv("RT_IIR4_MULT")) : 360.0;
+            double sr = getenv("RT_IIR4_SR") ? atof(getenv("RT_IIR4_SR")) : 48000.0;
+            generate_iir4_coefs(genDown.data(), genUp.data(), (int)nbin, C, tau, sr, p, mult);
+            genN = (int)nbin;
+        }
+        // down=1-up, so A=down, B=up
+        A1 = genDown.data(); B1 = genUp.data();
+        A2 = genDown.data(); B2 = genUp.data();
+    } else {
         extern const double kIIR_A1[]; extern const double kIIR_B1[];
         extern const double kIIR_A2[]; extern const double kIIR_B2[];
-    const double* A1 = ::kIIR_A1; const double* B1 = ::kIIR_B1;
+        A1 = ::kIIR_A1; B1 = ::kIIR_B1;
-    const double* A2 = ::kIIR_A2; const double* B2 = ::kIIR_B2;
+        A2 = ::kIIR_A2; B2 = ::kIIR_B2;
+    }
     double acc = 0.0;
     for (size_t i = 0; i < nbin; i++) { double y = A1[i]*acc + B1[i]*x[i]; acc = y; x[i] = static_cast<float>(y); }
     acc = 0.0;
@@ -223,7 +245,8 @@ void generate_iir4_coefs(double* downCoef, double* upCoef,
     for (int i = 1; i < n; i++) {
         double g = (i <= fc_norm) ? (fc_norm / i) : std::pow(fc_norm / i, p);
         double c = 1.0 / (g * tau / mult + 1.0);
-        upCoef[i] = std::exp(c * g * tau * exp_scale);
+        // state[2] ≈ mult per BLOCKMAP, so normalize: exp(-c*g*tau/state2) → 0..1
+        upCoef[i] = std::exp(-c * g * tau / mult * exp_scale);
         downCoef[i] = 1.0 - upCoef[i];
     }
 }

dsp/fn529fe0_check.cpp

@@ -195,6 +195,26 @@ int main() {
         if (!ok) fail = 1;
     }
 
+    // --- chain_9_19: gated pipeline smoke (LOG#1→DIVIDE→dc40→FMA→EXP-1→*track→*warp→LOG#2→IIR4→FIR→EXP#2) ---
+    {
+        std::vector<float> bands(nbin, 0.5f), tmp(nbin, 0.1f), acc(nbin, 0.0f);
+        std::vector<float> warp(nbin, 1.0f), att(nbin, 0.0f), rel(nbin, 0.0f);
+        std::vector<float> bands0 = bands;
+        fn529fe0::chain_9_19(bands.data(), tmp.data(), acc.data(), nullptr, warp.data(), att.data(), rel.data(), nbin);
+        bool ok = true;
+        for (size_t i = 0; i < nbin; i++) if (!std::isfinite(bands[i]) || bands[i] < 0.0f || bands[i] > 5.0f) ok = false;
+        std::printf("chain_9_19 smoke: in0=%.3f out0=%.3f outmid=%.3f finite=%d (%s)\n",
+                    bands0[0], bands[0], bands[nbin/2], ok, ok ? "OK" : "MISMATCH");
+        if (!ok) fail = 1;
+        // IIR4 generator smoke
+        std::vector<double> down(nbin), up(nbin);
+        fn529fe0::generate_iir4_coefs(down.data(), up.data(), (int)nbin, 1000.0, 1200.0, 48000.0, 0.5, 360.0);
+        bool gok = std::fabs(down[0]-1.0)<1e-9 && std::fabs(up[0])<1e-9 && down[1] < 1.0 && down[1] > 0.0;
+        std::printf("generate_iir4: down0=%.3f up0=%.3f down1=%.4f up1=%.4f (%s)\n",
+                    down[0], up[0], down[1], up[1], gok ? "OK" : "MISMATCH");
+        if (!gok) fail = 1;
+    }
+
     std::printf("fn529fe0 check %s\n", fail ? "FAIL" : "PASS");
     return fail;
 }