FIX: Properly handle series modification with /part and non-series values

resolves: Oldes/Rebol-issues#2683

Author: Oldes

.version

@@ -1 +1 @@
-3.21.2
+3.21.3

make/rebol3.nest

@@ -18,7 +18,7 @@ temp:     %make/tmp/
 stack-size: 4194304 ;= 4MB (4 * 1024 * 1024)
 optimize:   2
 
-version: 3.21.2
+version: 3.21.3
 
 ;flags: "-ggdb3"
 ;define: DEBUG

src/core/f-modify.c

@@ -3,7 +3,7 @@
 **  REBOL [R3] Language Interpreter and Run-time Environment
 **
 **  Copyright 2012 REBOL Technologies
-**  Copyright 2012-2024 Rebol Open Source Contributors
+**  Copyright 2012-2026 Rebol Open Source Contributors
 **  REBOL is a trademark of REBOL Technologies
 **
 **  Licensed under the Apache License, Version 2.0 (the "License");
@@ -186,7 +186,8 @@
 	}
 
 	// For INSERT or APPEND with /PART use the dst_len not src_len:
-	if (action != A_CHANGE && GET_FLAG(flags, AN_PART)) src_len = dst_len;
+	if (action != A_CHANGE && GET_FLAG(flags, AN_PART) && src_len > dst_len)
+		src_len = dst_len;
 
 	// If Source == Destination we need to prevent possible conflicts.
 	// Clone the argument just to be safe.

src/tests/units/series-test.r3

@@ -678,6 +678,10 @@ Rebol [
 	--test-- "unicode string"
 		;@@ https://github.com/Oldes/Rebol-issues/issues/2665
 		--assert (replace/all "<á]] <é]]" "]]" #">") == "<á> <é>"
+
+	--test-- "issue-2683"
+		;@@ https://github.com/Oldes/Rebol-issues/issues/2683
+		--assert "YaYb" = replace/all "XXXaXXXb" "XXX" #"Y"
 
 ===end-group===
 
@@ -754,6 +758,8 @@ Rebol [
 		;@@ https://github.com/Oldes/Rebol-issues/issues/2683
 		--assert "a" = append/part "" #"a" 10
 		--assert "←" = append/part "" #"^(2190)" 10
+		--assert "1" = append/part "" 1 10
+		--assert "1.1.1" = append/part "" 1.1.1 10
 ===end-group===
 
 ===start-group=== "APPEND ref!"