fix(navigator): resolve DO_JUMP when loading the current mission item

An external MISSION_SET_CURRENT sets the current sequence verbatim, with no
jump resolution. If it points directly at a DO_JUMP item, the navigator loaded
that jump as the current mission item. A DO_JUMP carries no position, so
setActiveMissionItems() never overwrote the current setpoint left behind by
reset_triplets() - an invalid IDLE setpoint. The vehicle then loitered in place
at altitude indefinitely, never resolving the jump and never completing the
mission (observed in a real flight).

Resolve the jump when loading the current item: follow it to its target without
consuming a repetition (a set-current is an out-of-band action, not a normal
traversal). For an already-resolved, non-jump current item this is a no-op, so
normal mission traversal is unaffected.

Also harden two related paths:
- getNonJumpItem() now reports failure instead of returning a still-unresolved
  DO_JUMP when it runs out of iterations (jump loop or a chain longer than
  MAX_JUMP_ITERATION), which would otherwise be loaded as the current item.
- treat a DO_JUMP as reached/completed in the mission block as a safety net, so
  the navigator advances rather than hanging should one ever reach that point.

Signed-off-by: RomanBapst <bapstroman@gmail.com>

src/modules/navigator/mission_base.cpp

@@ -542,15 +542,30 @@ MissionBase::set_mission_items()
 
 bool MissionBase::loadCurrentMissionItem()
 {
-	const bool success = loadMissionItemFromCache(_mission.current_seq, _mission_item);
+	// _mission.current_seq may point directly at a DO_JUMP item: it can be set verbatim by an
+	// external MISSION_SET_CURRENT (which does no jump resolution), or returned by a jump
+	// resolution that gave up. A DO_JUMP is not an executable current item, so resolve it to the
+	// next non-jump item here. We follow the jump to its target but do NOT consume a repetition
+	// (write_jumps == false), since a set-current is an out-of-band action, not a normal traversal.
+	// For an already-resolved (non-jump) current item this is a no-op.
+	int32_t resolved_index = _mission.current_seq;
+	mission_item_s resolved_item;
+
+	const bool success = getNonJumpItem(resolved_index, resolved_item, MissionTraversalType::FollowMissionControlFlow,
+					    /*write_jumps*/ false, /*mission_direction_backward*/ false) == PX4_OK;
 
 	if (!success) {
 		mavlink_log_critical(_navigator->get_mavlink_log_pub(), "Mission item could not be set.\t");
 		events::send(events::ID("mission_item_set_failed"), events::Log::Error,
 			     "Mission item could not be set");
+		return false;
 	}
 
-	return success;
+	// Persist the resolved index (republishes the mission topic only if it actually changed).
+	setMissionIndex(resolved_index);
+	_mission_item = resolved_item;
+
+	return true;
 }
 
 void MissionBase::setEndOfMissionItems()
@@ -1047,6 +1062,14 @@ int MissionBase::getNonJumpItem(int32_t &mission_index, mission_item_s &mission,
 		}
 	}
 
+	if (new_mission.nav_cmd == NAV_CMD_DO_JUMP) {
+		// Ran out of iterations while still on a DO_JUMP (e.g. a jump loop or a chain longer than
+		// MAX_JUMP_ITERATION). Report failure instead of returning an unresolved jump as a valid
+		// item, which would otherwise be loaded as the current mission item.
+		PX4_ERR("Do Jump could not be resolved within %u iterations.", MAX_JUMP_ITERATION);
+		return PX4_ERROR;
+	}
+
 	mission_index = new_mission_index;
 	mission = new_mission;
 

src/modules/navigator/mission_block.cpp

@@ -101,6 +101,11 @@ MissionBlock::is_mission_item_reached_or_completed()
 	case NAV_CMD_DO_SET_HOME:
 	case NAV_CMD_RETURN_TO_LAUNCH:
 
+	// Safety net: a DO_JUMP should never reach here as a current item (it is resolved in
+	// loadCurrentMissionItem), but if one ever does, treat it as complete so the navigator
+	// advances instead of hanging on an IDLE setpoint.
+	case NAV_CMD_DO_JUMP:
+
 		return true;
 
 	// Indefinite Waypoints