diff --git a/lib/core.sh b/lib/core.sh
index 9622120..ff26de1 100644
--- a/lib/core.sh
+++ b/lib/core.sh
@@ -299,6 +299,24 @@ resolve_target() {
     done
   fi
 
+  # Last resort: ask git for all worktrees (catches non-gtr-managed worktrees)
+  local wt_path wt_branch
+  while IFS= read -r line; do
+    case "$line" in
+      "worktree "*)  wt_path="${line#worktree }" ;;
+      "branch "*)
+        wt_branch="${line#branch refs/heads/}"
+        if [ "$wt_branch" = "$identifier" ]; then
+          local is_main=0
+          [ "$wt_path" = "$repo_root" ] && is_main=1
+          printf "%s\t%s\t%s\n" "$is_main" "$wt_path" "$wt_branch"
+          return 0
+        fi
+        ;;
+      "")  wt_path="" ; wt_branch="" ;;
+    esac
+  done < <(git -C "$repo_root" worktree list --porcelain 2>/dev/null)
+
   log_error "Worktree not found for branch: $identifier"
   return 1
 }
diff --git a/tests/core_resolve_target.bats b/tests/core_resolve_target.bats
index 9ad196d..7d8f9b3 100644
--- a/tests/core_resolve_target.bats
+++ b/tests/core_resolve_target.bats
@@ -81,6 +81,18 @@ teardown() {
   [ "$status" -eq 1 ]
 }
 
+# ── porcelain fallback ─────────────────────────────────────────────────────────
+
+@test "resolve_target finds externally-created worktree via porcelain fallback" {
+  # Create a worktree with raw git (outside gtr-managed directory)
+  local ext_dir="${TEST_REPO}-external"
+  git -C "$TEST_REPO" worktree add "$ext_dir" -b external-branch --quiet
+  local result
+  result=$(resolve_target "external-branch" "$TEST_REPO" "$TEST_WORKTREES_DIR" "")
+  # Assert: found with is_main=0, correct branch, path ends with expected suffix
+  [[ "$result" == "0"$'\t'*"-external"$'\t'"external-branch" ]]
+}
+
 # ── discover_repo_root from worktree ──────────────────────────────────────────
 
 @test "discover_repo_root returns main repo root when called from a worktree" {