Keep an original by its path and its content, so a second original at one path is not discarded (hq ADR 0100)

internal/apply/hold.go

@@ -22,13 +22,19 @@ import (
 // first copy is the one that was there before the mesh.
 type Keep func(path string, content []byte, mode os.FileMode) (string, error)
 
-// KeepIn keeps originals under dir/kept, each named for the path it came from, readable by root
-// alone — a predecessor's configuration may carry its credentials.
+// KeepIn keeps originals under dir/kept, each named for the path it came from AND for what was in
+// it, readable by root alone — a predecessor's configuration may carry its credentials.
+//
+// **By content as well as path, because a path has more than one original.** A file held, let go
+// when its module was unassigned, rewritten by the predecessor and found again is a second
+// original; named by path alone the second copy was silently discarded while the report said it
+// was kept (novox/hq ADR 0100). The same content at the same path is kept once.
 func KeepIn(dir string) Keep {
 	return func(path string, content []byte, _ os.FileMode) (string, error) {
-		sum := sha256.Sum256([]byte(path))
-		kept := filepath.Join(dir, "kept",
-			hex.EncodeToString(sum[:])[:16]+"-"+filepath.Base(path))
+		where := sha256.Sum256([]byte(path))
+		what := sha256.Sum256(content)
+		kept := filepath.Join(dir, "kept", hex.EncodeToString(where[:])[:12]+"-"+
+			hex.EncodeToString(what[:])[:12]+"-"+filepath.Base(path))
 		if _, err := os.Lstat(kept); err == nil {
 			return kept, nil
 		}