Improve docs of get_merkle_preimage.h; remove stale TODO

diff --git a/src/handler/lib/get_merkle_preimage.c b/src/handler/lib/get_merkle_preimage.c
index 6bb0de1..ebce71e 100644
--- a/src/handler/lib/get_merkle_preimage.c
+++ b/src/handler/lib/get_merkle_preimage.c
@@ -11,8 +11,6 @@
 #include "debug.h"
 #include "sw.h"
 
-// TODO: refactor common code with stream_preimage.c
-
 int call_get_merkle_preimage(dispatcher_context_t *dispatcher_context,
                              const uint8_t hash[static 32],
                              uint8_t *out_ptr,
diff --git a/src/handler/lib/get_merkle_preimage.h b/src/handler/lib/get_merkle_preimage.h
index 1bd457b..7b367a0 100644
--- a/src/handler/lib/get_merkle_preimage.h
+++ b/src/handler/lib/get_merkle_preimage.h
@@ -4,12 +4,16 @@
 #include "dispatcher.h"
 
 /**
+ * Like call_get_preimage, but strips the leading 0x00 Merkle leaf prefix from the output.
+ * The hash is still verified over the full preimage (including the prefix byte).
+ *
  * In this flow, the HWW sends a CCMD_GET_PREIMAGE command with a SHA256 hash.
- * The client must respond with a the preimage (at most 254 bytes), prefixed by its length.
+ * The client must respond with the preimage (at most 254 bytes), prefixed by its length.
  * The flow fails with SW_WRONG_DATA_LENGTH if the response is too short; it will fail with
  * SW_INCORRECT_DATA if the computed hash does not match.
  *
- * Returns the length of the preimage on success, or a negative number in case of failure.
+ * Returns the length of the preimage without the prefix on success, or a negative number in case
+ * of failure.
  */
 int call_get_merkle_preimage(dispatcher_context_t *dispatcher_context,
                              const uint8_t hash[static 32],