chore: preserve current FreeRTOS and C card updates

doc/assets/a2-structure.puml

@@ -8,41 +8,46 @@ skinparam defaultFontSize 10
 skinparam classBorderColor #2c7794
 skinparam classBackgroundColor #edf6fa
 skinparam ArrowColor #8095a1
-title A2 STRUCTURE — in-band metadata and address order
+title A2 STRUCTURE — RV32 header, split and two-sided coalescing
 
 class "01 Block header" as HEADER {
   next : BlockLink_t*
   size : size_t
+  raw sizeof = 8 bytes on RV32
+  aligned xHeapStructSize = 16
 }
 class "Allocated block" as ALLOC {
-  02 header + 13 byte request
-  aligned total = 32 bytes
+  02 A: header + 24 byte request
+  aligned total = 48 bytes
   payload begins after header
 }
 class "03 Free remainder" as REM {
   own header
-  size = 224 bytes
+  free = 4032 bytes after A
 }
 
 HEADER *-- ALLOC : precedes payload
-ALLOC -down-> REM : split preserves 256
+ALLOC -down-> REM : first-fit + split
 
 class "04 Address-ordered free list" as LIST {
   previous < inserted < current
+  A < B < C+tail
 }
-class "05 Right neighbour" as RIGHT {
-  block + block.size == current
+class "05 Previous / left neighbour" as LEFT {
+  previous + previous.size == inserted
+  merge previous first
 }
-class "06 Left neighbour" as LEFT {
-  previous + previous.size == block
+class "06 Next / right neighbour" as RIGHT {
+  merged + merged.size == current
+  merge next second
 }
 
 REM -down-> LIST : insert by address
-LIST -down-> RIGHT : join first
-RIGHT -down-> LEFT : then join left
+LIST -down-> LEFT : heap_4 tests first
+LEFT -down-> RIGHT : then tests next
 
 note right of LIST
-Ordering makes both physical
-neighbours locally visible.
+Address order exposes both physical
+neighbours without scanning the arena.
 end note
 @enduml