fix(wear_levelling): shorten zero-size guard comments

components/wear_levelling/WL_Flash.cpp

@@ -578,10 +578,7 @@ esp_err_t WL_Flash::write(size_t dest_addr, const void *src, size_t size)
         return ESP_ERR_INVALID_STATE;
     }
     if (size == 0) {
-        // Nothing to do. Guard this explicitly: size is unsigned, so
+        // size==0: (size-1) unsigned underflow would OOB the caller buffer.
-        // `size - 1` below would otherwise wrap around to SIZE_MAX and turn
-        // "count" into a huge page count, walking far past the caller's
-        // buffer (see components/wear_levelling/host_test).
         return ESP_OK;
     }
     ESP_LOGD(TAG, "%s - dest_addr= 0x%08" PRIx32 ", size= 0x%08" PRIx32 , __func__, (uint32_t) dest_addr, (uint32_t) size);
@@ -604,8 +601,7 @@ esp_err_t WL_Flash::read(size_t src_addr, void *dest, size_t size)
         return ESP_ERR_INVALID_STATE;
     }
     if (size == 0) {
-        // See the matching guard in WL_Flash::write() above: size==0 must
+        // Same size==0 guard as write(); avoid (size-1) underflow below.
-        // not be allowed to reach the `size - 1` computation below.
         return ESP_OK;
     }
     ESP_LOGD(TAG, "%s - src_addr= 0x%08" PRIx32 ", size= 0x%08" PRIx32 , __func__, (uint32_t) src_addr, (uint32_t) size);

components/wear_levelling/host_test/main/test_wl.cpp

@@ -110,12 +110,7 @@ TEST_CASE("write and read with zero size are safe no-ops", "[wear_levelling]")
     result = wl_mount(partition, &wl_handle);
     REQUIRE(result == ESP_OK);
 
-    // wl_write()/wl_read() do not document size==0 as invalid (analogous to
+    // Zero-length wl_write/read must be no-ops; size==0 used to underflow (size-1) and OOB the buffer.
-    // POSIX write()/read() with count==0), so it must not be treated as an
-    // out-of-bounds request. Previously, WL_Flash::write()/read() computed
-    // `(size - 1) / wl_page_size` without checking for size==0 first; since
-    // size is unsigned, size==0 wrapped this to a huge page count and walked
-    // far past the caller-provided buffer.
     uint8_t dummy = 0xAA;
     result = wl_write(wl_handle, 0, &dummy, 0);
     REQUIRE(result == ESP_OK);