Harden Newton-Raphson gamma bounds, improve v0.20.0 test coverage

Add positive-gamma clamp in L1/L2/L3 Newton-Raphson iterations to
prevent divergence on extreme mass ratios. Add missing CREATE EXTENSION,
tighter L1/L2 precision checks (4 decimal places), lagrange_distance_oe
test with Ceres, L1-Earth-L2 ordering verification, and DE fallback
tests for planetary moon Lagrange functions.

src/lagrange.h

@@ -149,6 +149,8 @@ lagrange_corotating(double mu, int point_id, double *x, double *y)
                     return -1;
 
                 gamma_new = gamma - f / fp;
+                if (gamma_new <= 0.0)
+                    gamma_new = gamma * 0.5;  /* keep gamma positive */
                 if (fabs(gamma_new - gamma) < 1e-15)
                     break;
                 gamma = gamma_new;
@@ -184,6 +186,8 @@ lagrange_corotating(double mu, int point_id, double *x, double *y)
                     return -1;
 
                 gamma_new = gamma - f / fp;
+                if (gamma_new <= 0.0)
+                    gamma_new = gamma * 0.5;  /* keep gamma positive */
                 if (fabs(gamma_new - gamma) < 1e-15)
                     break;
                 gamma = gamma_new;
@@ -223,6 +227,8 @@ lagrange_corotating(double mu, int point_id, double *x, double *y)
                     return -1;
 
                 gamma_new = gamma - f / fp;
+                if (gamma_new <= 0.0)
+                    gamma_new = gamma * 0.5;  /* keep gamma positive */
                 if (fabs(gamma_new - gamma) < 1e-15)
                     break;
                 gamma = gamma_new;

test/expected/v020_features.out

@@ -1,6 +1,8 @@
 -- v020_features: Lagrange point support
 -- Tests Sun-planet, Earth-Moon, planetary moon Lagrange points,
 -- Hill radius, zone radius, DE fallback, and input validation.
+CREATE EXTENSION IF NOT EXISTS pg_orrery;
+NOTICE:  extension "pg_orrery" already exists, skipping
 -- Reference observer: Greenwich, UK
 \set obs '''(51.4769,-0.0005,0)'''
 -- Reference time: J2000 epoch (2000-01-01 12:00:00 UTC)
@@ -284,6 +286,86 @@ SELECT
  t
 (1 row)
 
+-- ============================================================
+-- Tighter L1/L2 precision (4 decimal places)
+-- ============================================================
+SELECT
+    round(helio_distance(lagrange_heliocentric(3, 1, :t ::timestamptz))::numeric, 4) AS earth_l1_dist;
+ earth_l1_dist 
+---------------
+        0.9735
+(1 row)
+
+SELECT
+    round(helio_distance(lagrange_heliocentric(3, 2, :t ::timestamptz))::numeric, 4) AS earth_l2_dist;
+ earth_l2_dist 
+---------------
+        0.9932
+(1 row)
+
+-- L1 and L2 bracket Earth's heliocentric distance
+SELECT
+    helio_distance(lagrange_heliocentric(3, 1, :t ::timestamptz))
+    <
+    helio_distance(planet_heliocentric(3, :t ::timestamptz))
+    AND
+    helio_distance(planet_heliocentric(3, :t ::timestamptz))
+    <
+    helio_distance(lagrange_heliocentric(3, 2, :t ::timestamptz))
+    AS l1_earth_l2_ordering;
+ l1_earth_l2_ordering 
+----------------------
+ t
+(1 row)
+
+-- ============================================================
+-- lagrange_distance_oe — Ceres distance from Jupiter L4
+-- Ceres orbits at ~2.77 AU, Jupiter L4 at ~5.2 AU, so distance > 2 AU
+-- ============================================================
+SELECT
+    round(lagrange_distance_oe(
+        5, 4,
+        oe_from_mpc('00001    3.33  0.12 K24AM  60.07966  73.42937   80.26860  10.58664  0.0789126  0.21406048   2.7660961  0 MPO838504  8738 115 1801-2024 0.65 M-v 30k MPCLINUX   0000      (1) Ceres              20240825'),
+        :t ::timestamptz
+    )::numeric, 2) AS ceres_jup_l4_dist;
+ ceres_jup_l4_dist 
+-------------------
+              3.03
+(1 row)
+
+-- Distance should be positive and > 2 AU (main belt vs Trojan zone)
+SELECT
+    lagrange_distance_oe(
+        5, 4,
+        oe_from_mpc('00001    3.33  0.12 K24AM  60.07966  73.42937   80.26860  10.58664  0.0789126  0.21406048   2.7660961  0 MPO838504  8738 115 1801-2024 0.65 M-v 30k MPCLINUX   0000      (1) Ceres              20240825'),
+        :t ::timestamptz
+    ) > 2.0 AS ceres_far_from_trojan;
+ ceres_far_from_trojan 
+-----------------------
+ t
+(1 row)
+
+-- ============================================================
+-- DE fallback for planetary moon Lagrange functions
+-- ============================================================
+SELECT
+    round(eq_ra(galilean_lagrange_equatorial_de(0, 4, :t ::timestamptz))::numeric, 4) =
+    round(eq_ra(galilean_lagrange_equatorial(0, 4, :t ::timestamptz))::numeric, 4)
+    AS galilean_de_fallback_matches;
+ galilean_de_fallback_matches 
+------------------------------
+ t
+(1 row)
+
+SELECT
+    round(eq_ra(saturn_moon_lagrange_equatorial_de(5, 1, :t ::timestamptz))::numeric, 4) =
+    round(eq_ra(saturn_moon_lagrange_equatorial(5, 1, :t ::timestamptz))::numeric, 4)
+    AS saturn_de_fallback_matches;
+ saturn_de_fallback_matches 
+----------------------------
+ t
+(1 row)
+
 -- ============================================================
 -- Input validation
 -- ============================================================

test/sql/v020_features.sql

@@ -2,6 +2,8 @@
 -- Tests Sun-planet, Earth-Moon, planetary moon Lagrange points,
 -- Hill radius, zone radius, DE fallback, and input validation.
 
+CREATE EXTENSION IF NOT EXISTS pg_orrery;
+
 -- Reference observer: Greenwich, UK
 \set obs '''(51.4769,-0.0005,0)'''
 
@@ -178,6 +180,61 @@ SELECT
     round(hill_radius(5, :t ::timestamptz)::numeric, 4)
     AS hill_de_matches_vsop;
 
+-- ============================================================
+-- Tighter L1/L2 precision (4 decimal places)
+-- ============================================================
+
+SELECT
+    round(helio_distance(lagrange_heliocentric(3, 1, :t ::timestamptz))::numeric, 4) AS earth_l1_dist;
+
+SELECT
+    round(helio_distance(lagrange_heliocentric(3, 2, :t ::timestamptz))::numeric, 4) AS earth_l2_dist;
+
+-- L1 and L2 bracket Earth's heliocentric distance
+SELECT
+    helio_distance(lagrange_heliocentric(3, 1, :t ::timestamptz))
+    <
+    helio_distance(planet_heliocentric(3, :t ::timestamptz))
+    AND
+    helio_distance(planet_heliocentric(3, :t ::timestamptz))
+    <
+    helio_distance(lagrange_heliocentric(3, 2, :t ::timestamptz))
+    AS l1_earth_l2_ordering;
+
+-- ============================================================
+-- lagrange_distance_oe — Ceres distance from Jupiter L4
+-- Ceres orbits at ~2.77 AU, Jupiter L4 at ~5.2 AU, so distance > 2 AU
+-- ============================================================
+
+SELECT
+    round(lagrange_distance_oe(
+        5, 4,
+        oe_from_mpc('00001    3.33  0.12 K24AM  60.07966  73.42937   80.26860  10.58664  0.0789126  0.21406048   2.7660961  0 MPO838504  8738 115 1801-2024 0.65 M-v 30k MPCLINUX   0000      (1) Ceres              20240825'),
+        :t ::timestamptz
+    )::numeric, 2) AS ceres_jup_l4_dist;
+
+-- Distance should be positive and > 2 AU (main belt vs Trojan zone)
+SELECT
+    lagrange_distance_oe(
+        5, 4,
+        oe_from_mpc('00001    3.33  0.12 K24AM  60.07966  73.42937   80.26860  10.58664  0.0789126  0.21406048   2.7660961  0 MPO838504  8738 115 1801-2024 0.65 M-v 30k MPCLINUX   0000      (1) Ceres              20240825'),
+        :t ::timestamptz
+    ) > 2.0 AS ceres_far_from_trojan;
+
+-- ============================================================
+-- DE fallback for planetary moon Lagrange functions
+-- ============================================================
+
+SELECT
+    round(eq_ra(galilean_lagrange_equatorial_de(0, 4, :t ::timestamptz))::numeric, 4) =
+    round(eq_ra(galilean_lagrange_equatorial(0, 4, :t ::timestamptz))::numeric, 4)
+    AS galilean_de_fallback_matches;
+
+SELECT
+    round(eq_ra(saturn_moon_lagrange_equatorial_de(5, 1, :t ::timestamptz))::numeric, 4) =
+    round(eq_ra(saturn_moon_lagrange_equatorial(5, 1, :t ::timestamptz))::numeric, 4)
+    AS saturn_de_fallback_matches;
+
 -- ============================================================
 -- Input validation
 -- ============================================================