backend/http: Return existing lock info from backend on conflict (#38144)

* Return existing lock info from http state backend on conflict

* Remove info from LockError if failed to read or unmarshal

* Add change to .changes

Author: nicholasngai

.changes/v1.15/BUG FIXES-20260210-113930.yaml

@@ -0,0 +1,3 @@
+kind: BUG FIXES
+body: 'backend: Return conflicting lock info from HTTP backend instead of the lock that failed to be taken'
+time: 2026-02-10T11:39:30.00000-08:00

internal/backend/remote-state/http/client.go

@@ -105,20 +105,18 @@ func (c *httpClient) Lock(info *statemgr.LockInfo) (string, error) {
 		body, err := ioutil.ReadAll(resp.Body)
 		if err != nil {
 			return "", &statemgr.LockError{
-				Info: info,
-				Err:  fmt.Errorf("HTTP remote state already locked, failed to read body"),
+				Err: fmt.Errorf("HTTP remote state already locked, failed to read body"),
 			}
 		}
 		existing := statemgr.LockInfo{}
 		err = json.Unmarshal(body, &existing)
 		if err != nil {
 			return "", &statemgr.LockError{
-				Info: info,
-				Err:  fmt.Errorf("HTTP remote state already locked, failed to unmarshal body"),
+				Err: fmt.Errorf("HTTP remote state already locked, failed to unmarshal body"),
 			}
 		}
 		return "", &statemgr.LockError{
-			Info: info,
+			Info: &existing,
 			Err:  fmt.Errorf("HTTP remote state already locked: ID=%s", existing.ID),
 		}
 	default: