Post PSY6 Modeling Gaps

[jd-lara]

• Flow-target tap (Qf/Qt) + PST P-flow (Pf/Pt): extends the quantity-agnostic λ-continuation; math gives the complex-tap branch flows $S_f=V_f\overline{I_f}$, the $\partial Q_f/\partial p$ and $\partial P_f/\partial\alpha$ sensitivities, and the sigmoid update.
• Remote generator PQV: the pinned-remote-voltage / free-reactive degree-of-freedom swap, with both a continuation device and an in-Jacobian encoding; flags that no PSY generator carries a regulated-bus field yet.
• Generator QV droop: the sloped $Q$–$V$ line, its residual row and Jacobian entries, and the $k\to0$ (PV) / $k\to\infty$ (PQ) limits.
• Bipolar/negative-pole DC: per-pole DC-KCL + ground/return path generalizing the monopolar DCNetwork, with the balanced-bipole and monopolar-reduction verification invariants.
• HVDC angle-droop (INELFE): $P_{dc}=\text{clamp}(P_0+k_\theta(\theta_f-\theta_t))$ as an angle-dependent injection with its four $\partial P/\partial\theta$ Jacobian terms — no new state variable.
• In-Jacobian simultaneous control: the bordered augmented system $F_\text{aug}(x,p)=0$, mapped onto the existing LCC/VSC tail-unknown pattern and the reserved stamp_control! seam.
• Controls under PowellDogLeg/LM: documents that TrustRegionACPowerFlow is Powell's dogleg (already supported); the real gap is LM, closed by loosening one guard, with the solver-invariance property as the acceptance test.