Fix LMS sequential gating when sort_order has gaps.

Resolve the immediate predecessor by sort_order (and id) instead of requiring sort_order - 1, so learners cannot skip locked programs, courses, or modules when ordering numbers are non-consecutive.

Co-authored-by: Cursor <cursoragent@cursor.com>

db/query/lms_progress.sql

@@ -1,11 +1,23 @@
 -- name: GetPreviousProgram :one
+-- Immediate predecessor by sort_order within the same category (gaps in sort_order are allowed).
 SELECT
     p2.*
 FROM
     programs AS p1
-    INNER JOIN programs AS p2 ON p2.sort_order = p1.sort_order - 1
+    INNER JOIN programs AS p2 ON p2.category = p1.category
+        AND (
+            p2.sort_order < p1.sort_order
+            OR (
+                p2.sort_order = p1.sort_order
+                AND p2.id < p1.id
+            )
+        )
 WHERE
-    p1.id = $1;
+    p1.id = $1
+ORDER BY
+    p2.sort_order DESC,
+    p2.id DESC
+LIMIT 1;
 
 -- name: GetPreviousCourseInProgram :one
 SELECT
@@ -13,9 +25,19 @@ SELECT
 FROM
     courses AS c1
     INNER JOIN courses AS c2 ON c2.program_id = c1.program_id
-    AND c2.sort_order = c1.sort_order - 1
+        AND (
+            c2.sort_order < c1.sort_order
+            OR (
+                c2.sort_order = c1.sort_order
+                AND c2.id < c1.id
+            )
+        )
 WHERE
-    c1.id = $1;
+    c1.id = $1
+ORDER BY
+    c2.sort_order DESC,
+    c2.id DESC
+LIMIT 1;
 
 -- name: GetPreviousModuleInCourse :one
 SELECT
@@ -23,9 +45,19 @@ SELECT
 FROM
     modules AS m1
     INNER JOIN modules AS m2 ON m2.course_id = m1.course_id
-    AND m2.sort_order = m1.sort_order - 1
+        AND (
+            m2.sort_order < m1.sort_order
+            OR (
+                m2.sort_order = m1.sort_order
+                AND m2.id < m1.id
+            )
+        )
 WHERE
-    m1.id = $1;
+    m1.id = $1
+ORDER BY
+    m2.sort_order DESC,
+    m2.id DESC
+LIMIT 1;
 
 -- name: GetPreviousLessonInModule :one
 SELECT

gen/db/lms_progress.sql.go

@@ -647,9 +647,19 @@ SELECT
 FROM
     courses AS c1
     INNER JOIN courses AS c2 ON c2.program_id = c1.program_id
-    AND c2.sort_order = c1.sort_order - 1
+        AND (
+            c2.sort_order < c1.sort_order
+            OR (
+                c2.sort_order = c1.sort_order
+                AND c2.id < c1.id
+            )
+        )
 WHERE
     c1.id = $1
+ORDER BY
+    c2.sort_order DESC,
+    c2.id DESC
+LIMIT 1
 `
 
 func (q *Queries) GetPreviousCourseInProgram(ctx context.Context, id int64) (Course, error) {
@@ -715,9 +725,19 @@ SELECT
 FROM
     modules AS m1
     INNER JOIN modules AS m2 ON m2.course_id = m1.course_id
-    AND m2.sort_order = m1.sort_order - 1
+        AND (
+            m2.sort_order < m1.sort_order
+            OR (
+                m2.sort_order = m1.sort_order
+                AND m2.id < m1.id
+            )
+        )
 WHERE
     m1.id = $1
+ORDER BY
+    m2.sort_order DESC,
+    m2.id DESC
+LIMIT 1
 `
 
 func (q *Queries) GetPreviousModuleInCourse(ctx context.Context, id int64) (Module, error) {
@@ -742,11 +762,23 @@ SELECT
     p2.id, p2.name, p2.description, p2.thumbnail, p2.created_at, p2.updated_at, p2.sort_order, p2.category
 FROM
     programs AS p1
-    INNER JOIN programs AS p2 ON p2.sort_order = p1.sort_order - 1
+    INNER JOIN programs AS p2 ON p2.category = p1.category
+        AND (
+            p2.sort_order < p1.sort_order
+            OR (
+                p2.sort_order = p1.sort_order
+                AND p2.id < p1.id
+            )
+        )
 WHERE
     p1.id = $1
+ORDER BY
+    p2.sort_order DESC,
+    p2.id DESC
+LIMIT 1
 `
 
+// Immediate predecessor by sort_order within the same category (gaps in sort_order are allowed).
 func (q *Queries) GetPreviousProgram(ctx context.Context, id int64) (Program, error) {
 	row := q.db.QueryRow(ctx, GetPreviousProgram, id)
 	var i Program