Fix pg_tle sizeof/INTERNALLENGTH mismatch, exact leaf recheck

The pg_tle struct has been 104 bytes since v0.1.0, but INTERNALLENGTH
is 112.  The size comment claimed "11 doubles (88 bytes)" — there are
10 (80 bytes).  Every palloc(sizeof(pg_tle)) across the codebase
allocated 104 bytes while PostgreSQL's datumCopy/heap_form_tuple
copied 112, causing an 8-byte overread.

Fix: add _reserved[8] to pg_tle, making sizeof(pg_tle) == 112.
This is backward compatible — existing on-disk tuples already have
112 bytes allocated (from typlen), with zeros in the trailing 8.

Also in gist_tle.c:
- Remove TLE_TYPLEN band-aid, use sizeof(pg_tle) everywhere
- Set recheck = false for leaf entries in consistent: the orbital
  key is computed identically to the SQL operator, so the GiST
  leaf check is exact (eliminates unnecessary heap fetches)

src/gist_tle.c

@@ -44,13 +44,7 @@ PG_FUNCTION_INFO_V1(gist_tle_distance);
 /* Floating-point comparison tolerance (km and radians) */
 #define KEY_EPSILON  1.0e-9
 
-/*
+/* sizeof(pg_tle) == 112, matching INTERNALLENGTH in CREATE TYPE. */
- * The SQL type's INTERNALLENGTH.  sizeof(pg_tle) is 104 due to struct
- * packing, but the SQL definition declares 112.  All allocations that
- * become index datums must use TLE_TYPLEN so that PostgreSQL's
- * index_form_tuple() never reads past the allocation.
- */
-#define TLE_TYPLEN 112
 
 /*
  * 2-D orbital key extracted from a TLE's mean elements.
@@ -240,10 +234,9 @@ tle_alt_distance(PG_FUNCTION_ARGS)
  * Leaf entries carry the full pg_tle; we compress to tle_orbital_key.
  * Internal entries are already tle_orbital_key from union operations.
  *
- * The allocation must be TLE_TYPLEN bytes (matching INTERNALLENGTH),
+ * The allocation must be sizeof(pg_tle) bytes — which matches
- * not sizeof(tle_orbital_key) or sizeof(pg_tle).  GiST's
+ * INTERNALLENGTH — not sizeof(tle_orbital_key).  GiST's
- * index_form_tuple() copies typlen bytes from the datum pointer;
+ * index_form_tuple() copies typlen bytes from the datum pointer.
- * under-allocating causes a heap buffer overread.
  */
 Datum
 gist_tle_compress(PG_FUNCTION_ARGS)
@@ -254,7 +247,7 @@ gist_tle_compress(PG_FUNCTION_ARGS)
 	if (entry->leafkey)
 	{
 		pg_tle			*tle = (pg_tle *) DatumGetPointer(entry->key);
-		tle_orbital_key	*key = (tle_orbital_key *) palloc0(TLE_TYPLEN);
+		tle_orbital_key	*key = (tle_orbital_key *) palloc0(sizeof(pg_tle));
 
 		tle_to_orbital_key(tle, key);
 
@@ -286,8 +279,10 @@ gist_tle_decompress(PG_FUNCTION_ARGS)
  * gist_tle_consistent -- can this subtree contain matches for the query?
  *
  * Checks overlap in both altitude AND inclination dimensions.
- * Always sets recheck = true because 2-D overlap is only a necessary
+ *
- * condition -- the real conjunction test requires propagation.
+ * For leaf entries, recheck = false: the orbital key is computed
+ * identically to the SQL operator, so the GiST check is exact.
+ * For internal nodes, recheck is irrelevant (GiST ignores it).
  */
 Datum
 gist_tle_consistent(PG_FUNCTION_ARGS)
@@ -303,7 +298,12 @@ gist_tle_consistent(PG_FUNCTION_ARGS)
 
 	tle_to_orbital_key(query, &query_key);
 
-	*recheck = true;
+	/*
+	 * Leaf keys are exact (same tle_to_orbital_key as the operator),
+	 * so no recheck needed.  For internal nodes PostgreSQL ignores
+	 * the flag, but we set true by convention.
+	 */
+	*recheck = !GIST_LEAF(entry);
 
 	switch (strategy)
 	{
@@ -353,7 +353,7 @@ gist_tle_union(PG_FUNCTION_ARGS)
 	tle_orbital_key	*result;
 	tle_orbital_key	*cur;
 
-	result = (tle_orbital_key *) palloc0(TLE_TYPLEN);
+	result = (tle_orbital_key *) palloc0(sizeof(pg_tle));
 	cur = (tle_orbital_key *) DatumGetPointer(entryvec->vector[0].key);
 	*result = *cur;
 
@@ -363,7 +363,7 @@ gist_tle_union(PG_FUNCTION_ARGS)
 		key_merge(result, cur);
 	}
 
-	*sizep = TLE_TYPLEN;
+	*sizep = sizeof(pg_tle);
 
 	PG_RETURN_POINTER(result);
 }
@@ -508,8 +508,8 @@ gist_tle_picksplit(PG_FUNCTION_ARGS)
 	splitvec->spl_nright = 0;
 
 	/* Compute union keys and assign entries */
-	left_union  = (tle_orbital_key *) palloc0(TLE_TYPLEN);
+	left_union  = (tle_orbital_key *) palloc0(sizeof(pg_tle));
-	right_union = (tle_orbital_key *) palloc0(TLE_TYPLEN);
+	right_union = (tle_orbital_key *) palloc0(sizeof(pg_tle));
 
 	/* Seed the unions from the first entry in each half */
 	cur = (tle_orbital_key *) DatumGetPointer(

src/types.h

@@ -75,10 +75,13 @@ typedef struct pg_tle
     char        classification; /* U = unclassified */
     char        ephemeris_type; /* 0 = SGP4/SDP4 default */
     char        intl_desig[9];  /* international designator, null-terminated */
-    char        _pad;           /* alignment */
+    char        _pad;           /* alignment to int32 boundary */
+    char        _reserved[8];   /* match INTERNALLENGTH = 112 */
 } pg_tle;
 
-/* Size: 11 doubles (88 bytes) + 3 int32 (12 bytes) + 12 chars = 112 bytes */
+/* Size: 10 doubles (80) + 3 int32 (12) + 12 chars + 8 reserved = 112 bytes
+ * Must match INTERNALLENGTH in CREATE TYPE.  PostgreSQL's datumCopy() and
+ * heap_form_tuple() copy exactly typlen bytes from any pg_tle pointer. */
 
 
 /*